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android / platform / frameworks / support / 22e9d50663d0cc40d479cfbea79ed1097a4f5aa8 / . / recyclerview / recyclerview / src / main / java / androidx / recyclerview / widget / LinearLayoutManager.java
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/*
* Copyright 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.recyclerview.widget;
import static androidx.annotation.RestrictTo.Scope.LIBRARY;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.PointF;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.view.accessibility.AccessibilityEvent;
import androidx.annotation.NonNull;
import androidx.annotation.RestrictTo;
import androidx.core.os.TraceCompat;
import androidx.core.view.ViewCompat;
import java.util.List;
/**
* A {@link RecyclerView.LayoutManager} implementation which provides
* similar functionality to {@link android.widget.ListView}.
*/
public class LinearLayoutManager extends RecyclerView.LayoutManager implements
ItemTouchHelper.ViewDropHandler, RecyclerView.SmoothScroller.ScrollVectorProvider {
private static final String TAG = "LinearLayoutManager";
static final boolean DEBUG = false;
public static final int HORIZONTAL = RecyclerView.HORIZONTAL;
public static final int VERTICAL = RecyclerView.VERTICAL;
public static final int INVALID_OFFSET = Integer.MIN_VALUE;
/**
* While trying to find next view to focus, LayoutManager will not try to scroll more
* than this factor times the total space of the list. If layout is vertical, total space is the
* height minus padding, if layout is horizontal, total space is the width minus padding.
*/
private static final float MAX_SCROLL_FACTOR = 1 / 3f;
/**
* Current orientation. Either {@link #HORIZONTAL} or {@link #VERTICAL}
*/
@RecyclerView.Orientation
int mOrientation = RecyclerView.DEFAULT_ORIENTATION;
/**
* Helper class that keeps temporary layout state.
* It does not keep state after layout is complete but we still keep a reference to re-use
* the same object.
*/
private LayoutState mLayoutState;
/**
* Many calculations are made depending on orientation. To keep it clean, this interface
* helps {@link LinearLayoutManager} make those decisions.
*/
OrientationHelper mOrientationHelper;
/**
* We need to track this so that we can ignore current position when it changes.
*/
private boolean mLastStackFromEnd;
/**
* Defines if layout should be calculated from end to start.
*
* @see #mShouldReverseLayout
*/
private boolean mReverseLayout = false;
/**
* This keeps the final value for how LayoutManager should start laying out views.
* It is calculated by checking {@link #getReverseLayout()} and View's layout direction.
* {@link #onLayoutChildren(RecyclerView.Recycler, RecyclerView.State)} is run.
*/
boolean mShouldReverseLayout = false;
/**
* Works the same way as {@link android.widget.AbsListView#setStackFromBottom(boolean)} and
* it supports both orientations.
* see {@link android.widget.AbsListView#setStackFromBottom(boolean)}
*/
private boolean mStackFromEnd = false;
/**
* Works the same way as {@link android.widget.AbsListView#setSmoothScrollbarEnabled(boolean)}.
* see {@link android.widget.AbsListView#setSmoothScrollbarEnabled(boolean)}
*/
private boolean mSmoothScrollbarEnabled = true;
/**
* When LayoutManager needs to scroll to a position, it sets this variable and requests a
* layout which will check this variable and re-layout accordingly.
*/
int mPendingScrollPosition = RecyclerView.NO_POSITION;
/**
* Used to keep the offset value when {@link #scrollToPositionWithOffset(int, int)} is
* called.
*/
int mPendingScrollPositionOffset = INVALID_OFFSET;
private boolean mRecycleChildrenOnDetach;
SavedState mPendingSavedState = null;
/**
* Re-used variable to keep anchor information on re-layout.
* Anchor position and coordinate defines the reference point for LLM while doing a layout.
* */
final AnchorInfo mAnchorInfo = new AnchorInfo();
/**
* Stashed to avoid allocation, currently only used in #fill()
*/
private final LayoutChunkResult mLayoutChunkResult = new LayoutChunkResult();
/**
* Number of items to prefetch when first coming on screen with new data.
*/
private int mInitialPrefetchItemCount = 2;
// Reusable int array to be passed to method calls that mutate it in order to "return" two ints.
// This should only be used used transiently and should not be used to retain any state over
// time.
private int[] mReusableIntPair = new int[2];
/**
* Creates a vertical LinearLayoutManager
*
* @param context Current context, will be used to access resources.
*/
public LinearLayoutManager(Context context) {
this(context, RecyclerView.DEFAULT_ORIENTATION, false);
}
/**
* @param context Current context, will be used to access resources.
* @param orientation Layout orientation. Should be {@link #HORIZONTAL} or {@link
* #VERTICAL}.
* @param reverseLayout When set to true, layouts from end to start.
*/
public LinearLayoutManager(Context context, @RecyclerView.Orientation int orientation,
boolean reverseLayout) {
setOrientation(orientation);
setReverseLayout(reverseLayout);
}
/**
* Constructor used when layout manager is set in XML by RecyclerView attribute
* "layoutManager". Defaults to vertical orientation.
*
* {@link android.R.attr#orientation}
* {@link androidx.recyclerview.R.attr#reverseLayout}
* {@link androidx.recyclerview.R.attr#stackFromEnd}
*/
public LinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr,
int defStyleRes) {
Properties properties = getProperties(context, attrs, defStyleAttr, defStyleRes);
setOrientation(properties.orientation);
setReverseLayout(properties.reverseLayout);
setStackFromEnd(properties.stackFromEnd);
}
@Override
public boolean isAutoMeasureEnabled() {
return true;
}
/**
* {@inheritDoc}
*/
@Override
public RecyclerView.LayoutParams generateDefaultLayoutParams() {
return new RecyclerView.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
}
/**
* Returns whether LayoutManager will recycle its children when it is detached from
* RecyclerView.
*
* @return true if LayoutManager will recycle its children when it is detached from
* RecyclerView.
*/
public boolean getRecycleChildrenOnDetach() {
return mRecycleChildrenOnDetach;
}
/**
* Set whether LayoutManager will recycle its children when it is detached from
* RecyclerView.
* <p>
* If you are using a {@link RecyclerView.RecycledViewPool}, it might be a good idea to set
* this flag to <code>true</code> so that views will be available to other RecyclerViews
* immediately.
* <p>
* Note that, setting this flag will result in a performance drop if RecyclerView
* is restored.
*
* @param recycleChildrenOnDetach Whether children should be recycled in detach or not.
*/
public void setRecycleChildrenOnDetach(boolean recycleChildrenOnDetach) {
mRecycleChildrenOnDetach = recycleChildrenOnDetach;
}
@Override
public void onDetachedFromWindow(RecyclerView view, RecyclerView.Recycler recycler) {
super.onDetachedFromWindow(view, recycler);
if (mRecycleChildrenOnDetach) {
removeAndRecycleAllViews(recycler);
recycler.clear();
}
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
if (getChildCount() > 0) {
event.setFromIndex(findFirstVisibleItemPosition());
event.setToIndex(findLastVisibleItemPosition());
}
}
@Override
public Parcelable onSaveInstanceState() {
if (mPendingSavedState != null) {
return new SavedState(mPendingSavedState);
}
SavedState state = new SavedState();
if (getChildCount() > 0) {
ensureLayoutState();
boolean didLayoutFromEnd = mLastStackFromEnd ^ mShouldReverseLayout;
state.mAnchorLayoutFromEnd = didLayoutFromEnd;
if (didLayoutFromEnd) {
final View refChild = getChildClosestToEnd();
state.mAnchorOffset = mOrientationHelper.getEndAfterPadding()
- mOrientationHelper.getDecoratedEnd(refChild);
state.mAnchorPosition = getPosition(refChild);
} else {
final View refChild = getChildClosestToStart();
state.mAnchorPosition = getPosition(refChild);
state.mAnchorOffset = mOrientationHelper.getDecoratedStart(refChild)
- mOrientationHelper.getStartAfterPadding();
}
} else {
state.invalidateAnchor();
}
return state;
}
@Override
public void onRestoreInstanceState(Parcelable state) {
if (state instanceof SavedState) {
mPendingSavedState = (SavedState) state;
if (mPendingScrollPosition != RecyclerView.NO_POSITION) {
mPendingSavedState.invalidateAnchor();
}
requestLayout();
if (DEBUG) {
Log.d(TAG, "loaded saved state");
}
} else if (DEBUG) {
Log.d(TAG, "invalid saved state class");
}
}
/**
* @return true if {@link #getOrientation()} is {@link #HORIZONTAL}
*/
@Override
public boolean canScrollHorizontally() {
return mOrientation == HORIZONTAL;
}
/**
* @return true if {@link #getOrientation()} is {@link #VERTICAL}
*/
@Override
public boolean canScrollVertically() {
return mOrientation == VERTICAL;
}
/**
* Compatibility support for {@link android.widget.AbsListView#setStackFromBottom(boolean)}
*/
public void setStackFromEnd(boolean stackFromEnd) {
assertNotInLayoutOrScroll(null);
if (mStackFromEnd == stackFromEnd) {
return;
}
mStackFromEnd = stackFromEnd;
requestLayout();
}
public boolean getStackFromEnd() {
return mStackFromEnd;
}
/**
* Returns the current orientation of the layout.
*
* @return Current orientation, either {@link #HORIZONTAL} or {@link #VERTICAL}
* @see #setOrientation(int)
*/
@RecyclerView.Orientation
public int getOrientation() {
return mOrientation;
}
/**
* Sets the orientation of the layout. {@link LinearLayoutManager}
* will do its best to keep scroll position.
*
* @param orientation {@link #HORIZONTAL} or {@link #VERTICAL}
*/
public void setOrientation(@RecyclerView.Orientation int orientation) {
if (orientation != HORIZONTAL && orientation != VERTICAL) {
throw new IllegalArgumentException("invalid orientation:" + orientation);
}
assertNotInLayoutOrScroll(null);
if (orientation != mOrientation || mOrientationHelper == null) {
mOrientationHelper =
OrientationHelper.createOrientationHelper(this, orientation);
mAnchorInfo.mOrientationHelper = mOrientationHelper;
mOrientation = orientation;
requestLayout();
}
}
/**
* Calculates the view layout order. (e.g. from end to start or start to end)
* RTL layout support is applied automatically. So if layout is RTL and
* {@link #getReverseLayout()} is {@code true}, elements will be laid out starting from left.
*/
private void resolveShouldLayoutReverse() {
// A == B is the same result, but we rather keep it readable
if (mOrientation == VERTICAL || !isLayoutRTL()) {
mShouldReverseLayout = mReverseLayout;
} else {
mShouldReverseLayout = !mReverseLayout;
}
}
/**
* Returns if views are laid out from the opposite direction of the layout.
*
* @return If layout is reversed or not.
* @see #setReverseLayout(boolean)
*/
public boolean getReverseLayout() {
return mReverseLayout;
}
/**
* Used to reverse item traversal and layout order.
* This behaves similar to the layout change for RTL views. When set to true, first item is
* laid out at the end of the UI, second item is laid out before it etc.
*
* For horizontal layouts, it depends on the layout direction.
* When set to true, If {@link RecyclerView} is LTR, than it will
* layout from RTL, if {@link RecyclerView}} is RTL, it will layout
* from LTR.
*
* If you are looking for the exact same behavior of
* {@link android.widget.AbsListView#setStackFromBottom(boolean)}, use
* {@link #setStackFromEnd(boolean)}
*/
public void setReverseLayout(boolean reverseLayout) {
assertNotInLayoutOrScroll(null);
if (reverseLayout == mReverseLayout) {
return;
}
mReverseLayout = reverseLayout;
requestLayout();
}
/**
* {@inheritDoc}
*/
@Override
public View findViewByPosition(int position) {
final int childCount = getChildCount();
if (childCount == 0) {
return null;
}
final int firstChild = getPosition(getChildAt(0));
final int viewPosition = position - firstChild;
if (viewPosition >= 0 && viewPosition < childCount) {
final View child = getChildAt(viewPosition);
if (getPosition(child) == position) {
return child; // in pre-layout, this may not match
}
}
// fallback to traversal. This might be necessary in pre-layout.
return super.findViewByPosition(position);
}
/**
* <p>Returns the amount of extra space that should be laid out by LayoutManager.</p>
*
* <p>By default, {@link LinearLayoutManager} lays out 1 extra page
* of items while smooth scrolling and 0 otherwise. You can override this method to implement
* your custom layout pre-cache logic.</p>
*
* <p><strong>Note:</strong>Laying out invisible elements generally comes with significant
* performance cost. It's typically only desirable in places like smooth scrolling to an unknown
* location, where 1) the extra content helps LinearLayoutManager know in advance when its
* target is approaching, so it can decelerate early and smoothly and 2) while motion is
* continuous.</p>
*
* <p>Extending the extra layout space is especially expensive if done while the user may change
* scrolling direction. Changing direction will cause the extra layout space to swap to the
* opposite side of the viewport, incurring many rebinds/recycles, unless the cache is large
* enough to handle it.</p>
*
* @return The extra space that should be laid out (in pixels).
* @deprecated Use {@link #calculateExtraLayoutSpace(RecyclerView.State, int[])} instead.
*/
@SuppressWarnings("DeprecatedIsStillUsed")
@Deprecated
protected int getExtraLayoutSpace(RecyclerView.State state) {
if (state.hasTargetScrollPosition()) {
return mOrientationHelper.getTotalSpace();
} else {
return 0;
}
}
/**
* <p>Calculates the amount of extra space (in pixels) that should be laid out by {@link
* LinearLayoutManager} and stores the result in {@code extraLayoutSpace}. {@code
* extraLayoutSpace[0]} should be used for the extra space at the top/left, and {@code
* extraLayoutSpace[1]} should be used for the extra space at the bottom/right (depending on the
* orientation). Thus, the side where it is applied is unaffected by {@link
* #getLayoutDirection()} (LTR vs RTL), {@link #getStackFromEnd()} and {@link
* #getReverseLayout()}. Negative values are ignored.</p>
*
* <p>By default, {@code LinearLayoutManager} lays out 1 extra page of items while smooth
* scrolling, in the direction of the scroll, and no extra space is laid out in all other
* situations. You can override this method to implement your own custom pre-cache logic. Use
* {@link RecyclerView.State#hasTargetScrollPosition()} to find out if a smooth scroll to a
* position is in progress, and {@link RecyclerView.State#getTargetScrollPosition()} to find out
* which item it is scrolling to.</p>
*
* <p><strong>Note:</strong>Laying out extra items generally comes with significant performance
* cost. It's typically only desirable in places like smooth scrolling to an unknown location,
* where 1) the extra content helps LinearLayoutManager know in advance when its target is
* approaching, so it can decelerate early and smoothly and 2) while motion is continuous.</p>
*
* <p>Extending the extra layout space is especially expensive if done while the user may change
* scrolling direction. In the default implementation, changing direction will cause the extra
* layout space to swap to the opposite side of the viewport, incurring many rebinds/recycles,
* unless the cache is large enough to handle it.</p>
*/
protected void calculateExtraLayoutSpace(@NonNull RecyclerView.State state,
@NonNull int[] extraLayoutSpace) {
int extraLayoutSpaceStart = 0;
int extraLayoutSpaceEnd = 0;
// If calculateExtraLayoutSpace is not overridden, call the
// deprecated getExtraLayoutSpace for backwards compatibility
@SuppressWarnings("deprecation")
int extraScrollSpace = getExtraLayoutSpace(state);
if (mLayoutState.mLayoutDirection == LayoutState.LAYOUT_START) {
extraLayoutSpaceStart = extraScrollSpace;
} else {
extraLayoutSpaceEnd = extraScrollSpace;
}
extraLayoutSpace[0] = extraLayoutSpaceStart;
extraLayoutSpace[1] = extraLayoutSpaceEnd;
}
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
LinearSmoothScroller linearSmoothScroller =
new LinearSmoothScroller(recyclerView.getContext());
linearSmoothScroller.setTargetPosition(position);
startSmoothScroll(linearSmoothScroller);
}
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
if (getChildCount() == 0) {
return null;
}
final int firstChildPos = getPosition(getChildAt(0));
final int direction = targetPosition < firstChildPos != mShouldReverseLayout ? -1 : 1;
if (mOrientation == HORIZONTAL) {
return new PointF(direction, 0);
} else {
return new PointF(0, direction);
}
}
/**
* {@inheritDoc}
*/
@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
// layout algorithm:
// 1) by checking children and other variables, find an anchor coordinate and an anchor
// item position.
// 2) fill towards start, stacking from bottom
// 3) fill towards end, stacking from top
// 4) scroll to fulfill requirements like stack from bottom.
// create layout state
if (DEBUG) {
Log.d(TAG, "is pre layout:" + state.isPreLayout());
}
if (mPendingSavedState != null || mPendingScrollPosition != RecyclerView.NO_POSITION) {
if (state.getItemCount() == 0) {
removeAndRecycleAllViews(recycler);
return;
}
}
if (mPendingSavedState != null && mPendingSavedState.hasValidAnchor()) {
mPendingScrollPosition = mPendingSavedState.mAnchorPosition;
}
ensureLayoutState();
mLayoutState.mRecycle = false;
// resolve layout direction
resolveShouldLayoutReverse();
final View focused = getFocusedChild();
if (!mAnchorInfo.mValid || mPendingScrollPosition != RecyclerView.NO_POSITION
|| mPendingSavedState != null) {
mAnchorInfo.reset();
mAnchorInfo.mLayoutFromEnd = mShouldReverseLayout ^ mStackFromEnd;
// calculate anchor position and coordinate
updateAnchorInfoForLayout(recycler, state, mAnchorInfo);
mAnchorInfo.mValid = true;
} else if (focused != null && (mOrientationHelper.getDecoratedStart(focused)
>= mOrientationHelper.getEndAfterPadding()
|| mOrientationHelper.getDecoratedEnd(focused)
<= mOrientationHelper.getStartAfterPadding())) {
// This case relates to when the anchor child is the focused view and due to layout
// shrinking the focused view fell outside the viewport, e.g. when soft keyboard shows
// up after tapping an EditText which shrinks RV causing the focused view (The tapped
// EditText which is the anchor child) to get kicked out of the screen. Will update the
// anchor coordinate in order to make sure that the focused view is laid out. Otherwise,
// the available space in layoutState will be calculated as negative preventing the
// focused view from being laid out in fill.
// Note that we won't update the anchor position between layout passes (refer to
// TestResizingRelayoutWithAutoMeasure), which happens if we were to call
// updateAnchorInfoForLayout for an anchor that's not the focused view (e.g. a reference
// child which can change between layout passes).
mAnchorInfo.assignFromViewAndKeepVisibleRect(focused, getPosition(focused));
}
if (DEBUG) {
Log.d(TAG, "Anchor info:" + mAnchorInfo);
}
// LLM may decide to layout items for "extra" pixels to account for scrolling target,
// caching or predictive animations.
mLayoutState.mLayoutDirection = mLayoutState.mLastScrollDelta >= 0
? LayoutState.LAYOUT_END : LayoutState.LAYOUT_START;
mReusableIntPair[0] = 0;
mReusableIntPair[1] = 0;
calculateExtraLayoutSpace(state, mReusableIntPair);
int extraForStart = Math.max(0, mReusableIntPair[0])
+ mOrientationHelper.getStartAfterPadding();
int extraForEnd = Math.max(0, mReusableIntPair[1])
+ mOrientationHelper.getEndPadding();
if (state.isPreLayout() && mPendingScrollPosition != RecyclerView.NO_POSITION
&& mPendingScrollPositionOffset != INVALID_OFFSET) {
// if the child is visible and we are going to move it around, we should layout
// extra items in the opposite direction to make sure new items animate nicely
// instead of just fading in
final View existing = findViewByPosition(mPendingScrollPosition);
if (existing != null) {
final int current;
final int upcomingOffset;
if (mShouldReverseLayout) {
current = mOrientationHelper.getEndAfterPadding()
- mOrientationHelper.getDecoratedEnd(existing);
upcomingOffset = current - mPendingScrollPositionOffset;
} else {
current = mOrientationHelper.getDecoratedStart(existing)
- mOrientationHelper.getStartAfterPadding();
upcomingOffset = mPendingScrollPositionOffset - current;
}
if (upcomingOffset > 0) {
extraForStart += upcomingOffset;
} else {
extraForEnd -= upcomingOffset;
}
}
}
int startOffset;
int endOffset;
final int firstLayoutDirection;
if (mAnchorInfo.mLayoutFromEnd) {
firstLayoutDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_TAIL
: LayoutState.ITEM_DIRECTION_HEAD;
} else {
firstLayoutDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_HEAD
: LayoutState.ITEM_DIRECTION_TAIL;
}
onAnchorReady(recycler, state, mAnchorInfo, firstLayoutDirection);
detachAndScrapAttachedViews(recycler);
mLayoutState.mInfinite = resolveIsInfinite();
mLayoutState.mIsPreLayout = state.isPreLayout();
// noRecycleSpace not needed: recycling doesn't happen in below's fill
// invocations because mScrollingOffset is set to SCROLLING_OFFSET_NaN
mLayoutState.mNoRecycleSpace = 0;
if (mAnchorInfo.mLayoutFromEnd) {
// fill towards start
updateLayoutStateToFillStart(mAnchorInfo);
mLayoutState.mExtraFillSpace = extraForStart;
fill(recycler, mLayoutState, state, false);
startOffset = mLayoutState.mOffset;
final int firstElement = mLayoutState.mCurrentPosition;
if (mLayoutState.mAvailable > 0) {
extraForEnd += mLayoutState.mAvailable;
}
// fill towards end
updateLayoutStateToFillEnd(mAnchorInfo);
mLayoutState.mExtraFillSpace = extraForEnd;
mLayoutState.mCurrentPosition += mLayoutState.mItemDirection;
fill(recycler, mLayoutState, state, false);
endOffset = mLayoutState.mOffset;
if (mLayoutState.mAvailable > 0) {
// end could not consume all. add more items towards start
extraForStart = mLayoutState.mAvailable;
updateLayoutStateToFillStart(firstElement, startOffset);
mLayoutState.mExtraFillSpace = extraForStart;
fill(recycler, mLayoutState, state, false);
startOffset = mLayoutState.mOffset;
}
} else {
// fill towards end
updateLayoutStateToFillEnd(mAnchorInfo);
mLayoutState.mExtraFillSpace = extraForEnd;
fill(recycler, mLayoutState, state, false);
endOffset = mLayoutState.mOffset;
final int lastElement = mLayoutState.mCurrentPosition;
if (mLayoutState.mAvailable > 0) {
extraForStart += mLayoutState.mAvailable;
}
// fill towards start
updateLayoutStateToFillStart(mAnchorInfo);
mLayoutState.mExtraFillSpace = extraForStart;
mLayoutState.mCurrentPosition += mLayoutState.mItemDirection;
fill(recycler, mLayoutState, state, false);
startOffset = mLayoutState.mOffset;
if (mLayoutState.mAvailable > 0) {
extraForEnd = mLayoutState.mAvailable;
// start could not consume all it should. add more items towards end
updateLayoutStateToFillEnd(lastElement, endOffset);
mLayoutState.mExtraFillSpace = extraForEnd;
fill(recycler, mLayoutState, state, false);
endOffset = mLayoutState.mOffset;
}
}
// changes may cause gaps on the UI, try to fix them.
// TODO we can probably avoid this if neither stackFromEnd/reverseLayout/RTL values have
// changed
if (getChildCount() > 0) {
// because layout from end may be changed by scroll to position
// we re-calculate it.
// find which side we should check for gaps.
if (mShouldReverseLayout ^ mStackFromEnd) {
int fixOffset = fixLayoutEndGap(endOffset, recycler, state, true);
startOffset += fixOffset;
endOffset += fixOffset;
fixOffset = fixLayoutStartGap(startOffset, recycler, state, false);
startOffset += fixOffset;
endOffset += fixOffset;
} else {
int fixOffset = fixLayoutStartGap(startOffset, recycler, state, true);
startOffset += fixOffset;
endOffset += fixOffset;
fixOffset = fixLayoutEndGap(endOffset, recycler, state, false);
startOffset += fixOffset;
endOffset += fixOffset;
}
}
layoutForPredictiveAnimations(recycler, state, startOffset, endOffset);
if (!state.isPreLayout()) {
mOrientationHelper.onLayoutComplete();
} else {
mAnchorInfo.reset();
}
mLastStackFromEnd = mStackFromEnd;
if (DEBUG) {
validateChildOrder();
}
}
@Override
public void onLayoutCompleted(RecyclerView.State state) {
super.onLayoutCompleted(state);
mPendingSavedState = null; // we don't need this anymore
mPendingScrollPosition = RecyclerView.NO_POSITION;
mPendingScrollPositionOffset = INVALID_OFFSET;
mAnchorInfo.reset();
}
/**
* Method called when Anchor position is decided. Extending class can setup accordingly or
* even update anchor info if necessary.
* @param recycler The recycler for the layout
* @param state The layout state
* @param anchorInfo The mutable POJO that keeps the position and offset.
* @param firstLayoutItemDirection The direction of the first layout filling in terms of adapter
* indices.
*/
void onAnchorReady(RecyclerView.Recycler recycler, RecyclerView.State state,
AnchorInfo anchorInfo, int firstLayoutItemDirection) {
}
/**
* If necessary, layouts new items for predictive animations
*/
private void layoutForPredictiveAnimations(RecyclerView.Recycler recycler,
RecyclerView.State state, int startOffset,
int endOffset) {
// If there are scrap children that we did not layout, we need to find where they did go
// and layout them accordingly so that animations can work as expected.
// This case may happen if new views are added or an existing view expands and pushes
// another view out of bounds.
if (!state.willRunPredictiveAnimations() || getChildCount() == 0 || state.isPreLayout()
|| !supportsPredictiveItemAnimations()) {
return;
}
// to make the logic simpler, we calculate the size of children and call fill.
int scrapExtraStart = 0, scrapExtraEnd = 0;
final List<RecyclerView.ViewHolder> scrapList = recycler.getScrapList();
final int scrapSize = scrapList.size();
final int firstChildPos = getPosition(getChildAt(0));
for (int i = 0; i < scrapSize; i++) {
RecyclerView.ViewHolder scrap = scrapList.get(i);
if (scrap.isRemoved()) {
continue;
}
final int position = scrap.getLayoutPosition();
final int direction = position < firstChildPos != mShouldReverseLayout
? LayoutState.LAYOUT_START : LayoutState.LAYOUT_END;
if (direction == LayoutState.LAYOUT_START) {
scrapExtraStart += mOrientationHelper.getDecoratedMeasurement(scrap.itemView);
} else {
scrapExtraEnd += mOrientationHelper.getDecoratedMeasurement(scrap.itemView);
}
}
if (DEBUG) {
Log.d(TAG, "for unused scrap, decided to add " + scrapExtraStart
+ " towards start and " + scrapExtraEnd + " towards end");
}
mLayoutState.mScrapList = scrapList;
if (scrapExtraStart > 0) {
View anchor = getChildClosestToStart();
updateLayoutStateToFillStart(getPosition(anchor), startOffset);
mLayoutState.mExtraFillSpace = scrapExtraStart;
mLayoutState.mAvailable = 0;
mLayoutState.assignPositionFromScrapList();
fill(recycler, mLayoutState, state, false);
}
if (scrapExtraEnd > 0) {
View anchor = getChildClosestToEnd();
updateLayoutStateToFillEnd(getPosition(anchor), endOffset);
mLayoutState.mExtraFillSpace = scrapExtraEnd;
mLayoutState.mAvailable = 0;
mLayoutState.assignPositionFromScrapList();
fill(recycler, mLayoutState, state, false);
}
mLayoutState.mScrapList = null;
}
private void updateAnchorInfoForLayout(RecyclerView.Recycler recycler, RecyclerView.State state,
AnchorInfo anchorInfo) {
if (updateAnchorFromPendingData(state, anchorInfo)) {
if (DEBUG) {
Log.d(TAG, "updated anchor info from pending information");
}
return;
}
if (updateAnchorFromChildren(recycler, state, anchorInfo)) {
if (DEBUG) {
Log.d(TAG, "updated anchor info from existing children");
}
return;
}
if (DEBUG) {
Log.d(TAG, "deciding anchor info for fresh state");
}
anchorInfo.assignCoordinateFromPadding();
anchorInfo.mPosition = mStackFromEnd ? state.getItemCount() - 1 : 0;
}
/**
* Finds an anchor child from existing Views. Most of the time, this is the view closest to
* start or end that has a valid position (e.g. not removed).
* <p>
* If a child has focus, it is given priority.
*/
private boolean updateAnchorFromChildren(RecyclerView.Recycler recycler,
RecyclerView.State state, AnchorInfo anchorInfo) {
if (getChildCount() == 0) {
return false;
}
final View focused = getFocusedChild();
if (focused != null && anchorInfo.isViewValidAsAnchor(focused, state)) {
anchorInfo.assignFromViewAndKeepVisibleRect(focused, getPosition(focused));
return true;
}
if (mLastStackFromEnd != mStackFromEnd) {
return false;
}
View referenceChild = anchorInfo.mLayoutFromEnd
? findReferenceChildClosestToEnd(recycler, state)
: findReferenceChildClosestToStart(recycler, state);
if (referenceChild != null) {
anchorInfo.assignFromView(referenceChild, getPosition(referenceChild));
// If all visible views are removed in 1 pass, reference child might be out of bounds.
// If that is the case, offset it back to 0 so that we use these pre-layout children.
if (!state.isPreLayout() && supportsPredictiveItemAnimations()) {
// validate this child is at least partially visible. if not, offset it to start
final int childStart = mOrientationHelper.getDecoratedStart(referenceChild);
final int childEnd = mOrientationHelper.getDecoratedEnd(referenceChild);
final int boundsStart = mOrientationHelper.getStartAfterPadding();
final int boundsEnd = mOrientationHelper.getEndAfterPadding();
// b/148869110: usually if childStart >= boundsEnd the child is out of
// bounds, except if the child is 0 pixels!
final boolean notVisible = (childStart >= boundsEnd && childEnd > boundsEnd)
|| (childEnd <= boundsStart && childStart < boundsStart);
if (notVisible) {
anchorInfo.mCoordinate = anchorInfo.mLayoutFromEnd ? boundsEnd : boundsStart;
}
}
return true;
}
return false;
}
/**
* If there is a pending scroll position or saved states, updates the anchor info from that
* data and returns true
*/
private boolean updateAnchorFromPendingData(RecyclerView.State state, AnchorInfo anchorInfo) {
if (state.isPreLayout() || mPendingScrollPosition == RecyclerView.NO_POSITION) {
return false;
}
// validate scroll position
if (mPendingScrollPosition < 0 || mPendingScrollPosition >= state.getItemCount()) {
mPendingScrollPosition = RecyclerView.NO_POSITION;
mPendingScrollPositionOffset = INVALID_OFFSET;
if (DEBUG) {
Log.e(TAG, "ignoring invalid scroll position " + mPendingScrollPosition);
}
return false;
}
// if child is visible, try to make it a reference child and ensure it is fully visible.
// if child is not visible, align it depending on its virtual position.
anchorInfo.mPosition = mPendingScrollPosition;
if (mPendingSavedState != null && mPendingSavedState.hasValidAnchor()) {
// Anchor offset depends on how that child was laid out. Here, we update it
// according to our current view bounds
anchorInfo.mLayoutFromEnd = mPendingSavedState.mAnchorLayoutFromEnd;
if (anchorInfo.mLayoutFromEnd) {
anchorInfo.mCoordinate = mOrientationHelper.getEndAfterPadding()
- mPendingSavedState.mAnchorOffset;
} else {
anchorInfo.mCoordinate = mOrientationHelper.getStartAfterPadding()
+ mPendingSavedState.mAnchorOffset;
}
return true;
}
if (mPendingScrollPositionOffset == INVALID_OFFSET) {
View child = findViewByPosition(mPendingScrollPosition);
if (child != null) {
final int childSize = mOrientationHelper.getDecoratedMeasurement(child);
if (childSize > mOrientationHelper.getTotalSpace()) {
// item does not fit. fix depending on layout direction
anchorInfo.assignCoordinateFromPadding();
return true;
}
final int startGap = mOrientationHelper.getDecoratedStart(child)
- mOrientationHelper.getStartAfterPadding();
if (startGap < 0) {
anchorInfo.mCoordinate = mOrientationHelper.getStartAfterPadding();
anchorInfo.mLayoutFromEnd = false;
return true;
}
final int endGap = mOrientationHelper.getEndAfterPadding()
- mOrientationHelper.getDecoratedEnd(child);
if (endGap < 0) {
anchorInfo.mCoordinate = mOrientationHelper.getEndAfterPadding();
anchorInfo.mLayoutFromEnd = true;
return true;
}
anchorInfo.mCoordinate = anchorInfo.mLayoutFromEnd
? (mOrientationHelper.getDecoratedEnd(child) + mOrientationHelper
.getTotalSpaceChange())
: mOrientationHelper.getDecoratedStart(child);
} else { // item is not visible.
if (getChildCount() > 0) {
// get position of any child, does not matter
int pos = getPosition(getChildAt(0));
anchorInfo.mLayoutFromEnd = mPendingScrollPosition < pos
== mShouldReverseLayout;
}
anchorInfo.assignCoordinateFromPadding();
}
return true;
}
// override layout from end values for consistency
anchorInfo.mLayoutFromEnd = mShouldReverseLayout;
// if this changes, we should update prepareForDrop as well
if (mShouldReverseLayout) {
anchorInfo.mCoordinate = mOrientationHelper.getEndAfterPadding()
- mPendingScrollPositionOffset;
} else {
anchorInfo.mCoordinate = mOrientationHelper.getStartAfterPadding()
+ mPendingScrollPositionOffset;
}
return true;
}
/**
* @return The final offset amount for children
*/
private int fixLayoutEndGap(int endOffset, RecyclerView.Recycler recycler,
RecyclerView.State state, boolean canOffsetChildren) {
int gap = mOrientationHelper.getEndAfterPadding() - endOffset;
int fixOffset = 0;
if (gap > 0) {
fixOffset = -scrollBy(-gap, recycler, state);
} else {
return 0; // nothing to fix
}
// move offset according to scroll amount
endOffset += fixOffset;
if (canOffsetChildren) {
// re-calculate gap, see if we could fix it
gap = mOrientationHelper.getEndAfterPadding() - endOffset;
if (gap > 0) {
mOrientationHelper.offsetChildren(gap);
return gap + fixOffset;
}
}
return fixOffset;
}
/**
* @return The final offset amount for children
*/
private int fixLayoutStartGap(int startOffset, RecyclerView.Recycler recycler,
RecyclerView.State state, boolean canOffsetChildren) {
int gap = startOffset - mOrientationHelper.getStartAfterPadding();
int fixOffset = 0;
if (gap > 0) {
// check if we should fix this gap.
fixOffset = -scrollBy(gap, recycler, state);
} else {
return 0; // nothing to fix
}
startOffset += fixOffset;
if (canOffsetChildren) {
// re-calculate gap, see if we could fix it
gap = startOffset - mOrientationHelper.getStartAfterPadding();
if (gap > 0) {
mOrientationHelper.offsetChildren(-gap);
return fixOffset - gap;
}
}
return fixOffset;
}
private void updateLayoutStateToFillEnd(AnchorInfo anchorInfo) {
updateLayoutStateToFillEnd(anchorInfo.mPosition, anchorInfo.mCoordinate);
}
private void updateLayoutStateToFillEnd(int itemPosition, int offset) {
mLayoutState.mAvailable = mOrientationHelper.getEndAfterPadding() - offset;
mLayoutState.mItemDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_HEAD :
LayoutState.ITEM_DIRECTION_TAIL;
mLayoutState.mCurrentPosition = itemPosition;
mLayoutState.mLayoutDirection = LayoutState.LAYOUT_END;
mLayoutState.mOffset = offset;
mLayoutState.mScrollingOffset = LayoutState.SCROLLING_OFFSET_NaN;
}
private void updateLayoutStateToFillStart(AnchorInfo anchorInfo) {
updateLayoutStateToFillStart(anchorInfo.mPosition, anchorInfo.mCoordinate);
}
private void updateLayoutStateToFillStart(int itemPosition, int offset) {
mLayoutState.mAvailable = offset - mOrientationHelper.getStartAfterPadding();
mLayoutState.mCurrentPosition = itemPosition;
mLayoutState.mItemDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_TAIL :
LayoutState.ITEM_DIRECTION_HEAD;
mLayoutState.mLayoutDirection = LayoutState.LAYOUT_START;
mLayoutState.mOffset = offset;
mLayoutState.mScrollingOffset = LayoutState.SCROLLING_OFFSET_NaN;
}
protected boolean isLayoutRTL() {
return getLayoutDirection() == ViewCompat.LAYOUT_DIRECTION_RTL;
}
void ensureLayoutState() {
if (mLayoutState == null) {
mLayoutState = createLayoutState();
}
}
/**
* Test overrides this to plug some tracking and verification.
*
* @return A new LayoutState
*/
LayoutState createLayoutState() {
return new LayoutState();
}
/**
* <p>Scroll the RecyclerView to make the position visible.</p>
*
* <p>RecyclerView will scroll the minimum amount that is necessary to make the
* target position visible. If you are looking for a similar behavior to
* {@link android.widget.ListView#setSelection(int)} or
* {@link android.widget.ListView#setSelectionFromTop(int, int)}, use
* {@link #scrollToPositionWithOffset(int, int)}.</p>
*
* <p>Note that scroll position change will not be reflected until the next layout call.</p>
*
* @param position Scroll to this adapter position
* @see #scrollToPositionWithOffset(int, int)
*/
@Override
public void scrollToPosition(int position) {
mPendingScrollPosition = position;
mPendingScrollPositionOffset = INVALID_OFFSET;
if (mPendingSavedState != null) {
mPendingSavedState.invalidateAnchor();
}
requestLayout();
}
/**
* Scroll to the specified adapter position with the given offset from resolved layout
* start. Resolved layout start depends on {@link #getReverseLayout()},
* {@link ViewCompat#getLayoutDirection(android.view.View)} and {@link #getStackFromEnd()}.
* <p>
* For example, if layout is {@link #VERTICAL} and {@link #getStackFromEnd()} is true, calling
* <code>scrollToPositionWithOffset(10, 20)</code> will layout such that
* <code>item[10]</code>'s bottom is 20 pixels above the RecyclerView's bottom.
* <p>
* Note that scroll position change will not be reflected until the next layout call.
* <p>
* If you are just trying to make a position visible, use {@link #scrollToPosition(int)}.
*
* @param position Index (starting at 0) of the reference item.
* @param offset The distance (in pixels) between the start edge of the item view and
* start edge of the RecyclerView.
* @see #setReverseLayout(boolean)
* @see #scrollToPosition(int)
*/
public void scrollToPositionWithOffset(int position, int offset) {
mPendingScrollPosition = position;
mPendingScrollPositionOffset = offset;
if (mPendingSavedState != null) {
mPendingSavedState.invalidateAnchor();
}
requestLayout();
}
/**
* {@inheritDoc}
*/
@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler,
RecyclerView.State state) {
if (mOrientation == VERTICAL) {
return 0;
}
return scrollBy(dx, recycler, state);
}
/**
* {@inheritDoc}
*/
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler,
RecyclerView.State state) {
if (mOrientation == HORIZONTAL) {
return 0;
}
return scrollBy(dy, recycler, state);
}
@Override
public int computeHorizontalScrollOffset(RecyclerView.State state) {
return computeScrollOffset(state);
}
@Override
public int computeVerticalScrollOffset(RecyclerView.State state) {
return computeScrollOffset(state);
}
@Override
public int computeHorizontalScrollExtent(RecyclerView.State state) {
return computeScrollExtent(state);
}
@Override
public int computeVerticalScrollExtent(RecyclerView.State state) {
return computeScrollExtent(state);
}
@Override
public int computeHorizontalScrollRange(RecyclerView.State state) {
return computeScrollRange(state);
}
@Override
public int computeVerticalScrollRange(RecyclerView.State state) {
return computeScrollRange(state);
}
private int computeScrollOffset(RecyclerView.State state) {
if (getChildCount() == 0) {
return 0;
}
ensureLayoutState();
return ScrollbarHelper.computeScrollOffset(state, mOrientationHelper,
findFirstVisibleChildClosestToStart(!mSmoothScrollbarEnabled, true),
findFirstVisibleChildClosestToEnd(!mSmoothScrollbarEnabled, true),
this, mSmoothScrollbarEnabled, mShouldReverseLayout);
}
private int computeScrollExtent(RecyclerView.State state) {
if (getChildCount() == 0) {
return 0;
}
ensureLayoutState();
return ScrollbarHelper.computeScrollExtent(state, mOrientationHelper,
findFirstVisibleChildClosestToStart(!mSmoothScrollbarEnabled, true),
findFirstVisibleChildClosestToEnd(!mSmoothScrollbarEnabled, true),
this, mSmoothScrollbarEnabled);
}
private int computeScrollRange(RecyclerView.State state) {
if (getChildCount() == 0) {
return 0;
}
ensureLayoutState();
return ScrollbarHelper.computeScrollRange(state, mOrientationHelper,
findFirstVisibleChildClosestToStart(!mSmoothScrollbarEnabled, true),
findFirstVisibleChildClosestToEnd(!mSmoothScrollbarEnabled, true),
this, mSmoothScrollbarEnabled);
}
/**
* When smooth scrollbar is enabled, the position and size of the scrollbar thumb is computed
* based on the number of visible pixels in the visible items. This however assumes that all
* list items have similar or equal widths or heights (depending on list orientation).
* If you use a list in which items have different dimensions, the scrollbar will change
* appearance as the user scrolls through the list. To avoid this issue, you need to disable
* this property.
*
* When smooth scrollbar is disabled, the position and size of the scrollbar thumb is based
* solely on the number of items in the adapter and the position of the visible items inside
* the adapter. This provides a stable scrollbar as the user navigates through a list of items
* with varying widths / heights.
*
* @param enabled Whether or not to enable smooth scrollbar.
*
* @see #setSmoothScrollbarEnabled(boolean)
*/
public void setSmoothScrollbarEnabled(boolean enabled) {
mSmoothScrollbarEnabled = enabled;
}
/**
* Returns the current state of the smooth scrollbar feature. It is enabled by default.
*
* @return True if smooth scrollbar is enabled, false otherwise.
*
* @see #setSmoothScrollbarEnabled(boolean)
*/
public boolean isSmoothScrollbarEnabled() {
return mSmoothScrollbarEnabled;
}
private void updateLayoutState(int layoutDirection, int requiredSpace,
boolean canUseExistingSpace, RecyclerView.State state) {
// If parent provides a hint, don't measure unlimited.
mLayoutState.mInfinite = resolveIsInfinite();
mLayoutState.mLayoutDirection = layoutDirection;
mReusableIntPair[0] = 0;
mReusableIntPair[1] = 0;
calculateExtraLayoutSpace(state, mReusableIntPair);
int extraForStart = Math.max(0, mReusableIntPair[0]);
int extraForEnd = Math.max(0, mReusableIntPair[1]);
boolean layoutToEnd = layoutDirection == LayoutState.LAYOUT_END;
mLayoutState.mExtraFillSpace = layoutToEnd ? extraForEnd : extraForStart;
mLayoutState.mNoRecycleSpace = layoutToEnd ? extraForStart : extraForEnd;
int scrollingOffset;
if (layoutToEnd) {
mLayoutState.mExtraFillSpace += mOrientationHelper.getEndPadding();
// get the first child in the direction we are going
final View child = getChildClosestToEnd();
// the direction in which we are traversing children
mLayoutState.mItemDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_HEAD
: LayoutState.ITEM_DIRECTION_TAIL;
mLayoutState.mCurrentPosition = getPosition(child) + mLayoutState.mItemDirection;
mLayoutState.mOffset = mOrientationHelper.getDecoratedEnd(child);
// calculate how much we can scroll without adding new children (independent of layout)
scrollingOffset = mOrientationHelper.getDecoratedEnd(child)
- mOrientationHelper.getEndAfterPadding();
} else {
final View child = getChildClosestToStart();
mLayoutState.mExtraFillSpace += mOrientationHelper.getStartAfterPadding();
mLayoutState.mItemDirection = mShouldReverseLayout ? LayoutState.ITEM_DIRECTION_TAIL
: LayoutState.ITEM_DIRECTION_HEAD;
mLayoutState.mCurrentPosition = getPosition(child) + mLayoutState.mItemDirection;
mLayoutState.mOffset = mOrientationHelper.getDecoratedStart(child);
scrollingOffset = -mOrientationHelper.getDecoratedStart(child)
+ mOrientationHelper.getStartAfterPadding();
}
mLayoutState.mAvailable = requiredSpace;
if (canUseExistingSpace) {
mLayoutState.mAvailable -= scrollingOffset;
}
mLayoutState.mScrollingOffset = scrollingOffset;
}
boolean resolveIsInfinite() {
return mOrientationHelper.getMode() == View.MeasureSpec.UNSPECIFIED
&& mOrientationHelper.getEnd() == 0;
}
void collectPrefetchPositionsForLayoutState(RecyclerView.State state, LayoutState layoutState,
LayoutPrefetchRegistry layoutPrefetchRegistry) {
final int pos = layoutState.mCurrentPosition;
if (pos >= 0 && pos < state.getItemCount()) {
layoutPrefetchRegistry.addPosition(pos, Math.max(0, layoutState.mScrollingOffset));
}
}
@Override
public void collectInitialPrefetchPositions(int adapterItemCount,
LayoutPrefetchRegistry layoutPrefetchRegistry) {
final boolean fromEnd;
final int anchorPos;
if (mPendingSavedState != null && mPendingSavedState.hasValidAnchor()) {
// use restored state, since it hasn't been resolved yet
fromEnd = mPendingSavedState.mAnchorLayoutFromEnd;
anchorPos = mPendingSavedState.mAnchorPosition;
} else {
resolveShouldLayoutReverse();
fromEnd = mShouldReverseLayout;
if (mPendingScrollPosition == RecyclerView.NO_POSITION) {
anchorPos = fromEnd ? adapterItemCount - 1 : 0;
} else {
anchorPos = mPendingScrollPosition;
}
}
final int direction = fromEnd
? LayoutState.ITEM_DIRECTION_HEAD
: LayoutState.ITEM_DIRECTION_TAIL;
int targetPos = anchorPos;
for (int i = 0; i < mInitialPrefetchItemCount; i++) {
if (targetPos >= 0 && targetPos < adapterItemCount) {
layoutPrefetchRegistry.addPosition(targetPos, 0);
} else {
break; // no more to prefetch
}
targetPos += direction;
}
}
/**
* Sets the number of items to prefetch in
* {@link #collectInitialPrefetchPositions(int, LayoutPrefetchRegistry)}, which defines
* how many inner items should be prefetched when this LayoutManager's RecyclerView
* is nested inside another RecyclerView.
*
* <p>Set this value to the number of items this inner LayoutManager will display when it is
* first scrolled into the viewport. RecyclerView will attempt to prefetch that number of items
* so they are ready, avoiding jank as the inner RecyclerView is scrolled into the viewport.</p>
*
* <p>For example, take a vertically scrolling RecyclerView with horizontally scrolling inner
* RecyclerViews. The rows always have 4 items visible in them (or 5 if not aligned). Passing
* <code>4</code> to this method for each inner RecyclerView's LinearLayoutManager will enable
* RecyclerView's prefetching feature to do create/bind work for 4 views within a row early,
* before it is scrolled on screen, instead of just the default 2.</p>
*
* <p>Calling this method does nothing unless the LayoutManager is in a RecyclerView
* nested in another RecyclerView.</p>
*
* <p class="note"><strong>Note:</strong> Setting this value to be larger than the number of
* views that will be visible in this view can incur unnecessary bind work, and an increase to
* the number of Views created and in active use.</p>
*
* @param itemCount Number of items to prefetch
*
* @see #isItemPrefetchEnabled()
* @see #getInitialPrefetchItemCount()
* @see #collectInitialPrefetchPositions(int, LayoutPrefetchRegistry)
*/
public void setInitialPrefetchItemCount(int itemCount) {
mInitialPrefetchItemCount = itemCount;
}
/**
* Gets the number of items to prefetch in
* {@link #collectInitialPrefetchPositions(int, LayoutPrefetchRegistry)}, which defines
* how many inner items should be prefetched when this LayoutManager's RecyclerView
* is nested inside another RecyclerView.
*
* @see #isItemPrefetchEnabled()
* @see #setInitialPrefetchItemCount(int)
* @see #collectInitialPrefetchPositions(int, LayoutPrefetchRegistry)
*
* @return number of items to prefetch.
*/
public int getInitialPrefetchItemCount() {
return mInitialPrefetchItemCount;
}
@Override
public void collectAdjacentPrefetchPositions(int dx, int dy, RecyclerView.State state,
LayoutPrefetchRegistry layoutPrefetchRegistry) {
int delta = (mOrientation == HORIZONTAL) ? dx : dy;
if (getChildCount() == 0 || delta == 0) {
// can't support this scroll, so don't bother prefetching
return;
}
ensureLayoutState();
final int layoutDirection = delta > 0 ? LayoutState.LAYOUT_END : LayoutState.LAYOUT_START;
final int absDelta = Math.abs(delta);
updateLayoutState(layoutDirection, absDelta, true, state);
collectPrefetchPositionsForLayoutState(state, mLayoutState, layoutPrefetchRegistry);
}
int scrollBy(int delta, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getChildCount() == 0 || delta == 0) {
return 0;
}
ensureLayoutState();
mLayoutState.mRecycle = true;
final int layoutDirection = delta > 0 ? LayoutState.LAYOUT_END : LayoutState.LAYOUT_START;
final int absDelta = Math.abs(delta);
updateLayoutState(layoutDirection, absDelta, true, state);
final int consumed = mLayoutState.mScrollingOffset
+ fill(recycler, mLayoutState, state, false);
if (consumed < 0) {
if (DEBUG) {
Log.d(TAG, "Don't have any more elements to scroll");
}
return 0;
}
final int scrolled = absDelta > consumed ? layoutDirection * consumed : delta;
mOrientationHelper.offsetChildren(-scrolled);
if (DEBUG) {
Log.d(TAG, "scroll req: " + delta + " scrolled: " + scrolled);
}
mLayoutState.mLastScrollDelta = scrolled;
return scrolled;
}
@Override
public void assertNotInLayoutOrScroll(String message) {
if (mPendingSavedState == null) {
super.assertNotInLayoutOrScroll(message);
}
}
/**
* Recycles children between given indices.
*
* @param startIndex inclusive
* @param endIndex exclusive
*/
private void recycleChildren(RecyclerView.Recycler recycler, int startIndex, int endIndex) {
if (startIndex == endIndex) {
return;
}
if (DEBUG) {
Log.d(TAG, "Recycling " + Math.abs(startIndex - endIndex) + " items");
}
if (endIndex > startIndex) {
for (int i = endIndex - 1; i >= startIndex; i--) {
removeAndRecycleViewAt(i, recycler);
}
} else {
for (int i = startIndex; i > endIndex; i--) {
removeAndRecycleViewAt(i, recycler);
}
}
}
/**
* Recycles views that went out of bounds after scrolling towards the end of the layout.
* <p>
* Checks both layout position and visible position to guarantee that the view is not visible.
*
* @param recycler Recycler instance of {@link RecyclerView}
* @param scrollingOffset This can be used to add additional padding to the visible area. This
* is used to detect children that will go out of bounds after scrolling,
* without actually moving them.
* @param noRecycleSpace Extra space that should be excluded from recycling. This is the space
* from {@code extraLayoutSpace[0]}, calculated in {@link
* #calculateExtraLayoutSpace}.
*/
private void recycleViewsFromStart(RecyclerView.Recycler recycler, int scrollingOffset,
int noRecycleSpace) {
if (scrollingOffset < 0) {
if (DEBUG) {
Log.d(TAG, "Called recycle from start with a negative value. This might happen"
+ " during layout changes but may be sign of a bug");
}
return;
}
// ignore padding, ViewGroup may not clip children.
final int limit = scrollingOffset - noRecycleSpace;
final int childCount = getChildCount();
if (mShouldReverseLayout) {
for (int i = childCount - 1; i >= 0; i--) {
View child = getChildAt(i);
if (mOrientationHelper.getDecoratedEnd(child) > limit
|| mOrientationHelper.getTransformedEndWithDecoration(child) > limit) {
// stop here
recycleChildren(recycler, childCount - 1, i);
return;
}
}
} else {
for (int i = 0; i < childCount; i++) {
View child = getChildAt(i);
if (mOrientationHelper.getDecoratedEnd(child) > limit
|| mOrientationHelper.getTransformedEndWithDecoration(child) > limit) {
// stop here
recycleChildren(recycler, 0, i);
return;
}
}
}
}
/**
* Recycles views that went out of bounds after scrolling towards the start of the layout.
* <p>
* Checks both layout position and visible position to guarantee that the view is not visible.
*
* @param recycler Recycler instance of {@link RecyclerView}
* @param scrollingOffset This can be used to add additional padding to the visible area. This
* is used to detect children that will go out of bounds after scrolling,
* without actually moving them.
* @param noRecycleSpace Extra space that should be excluded from recycling. This is the space
* from {@code extraLayoutSpace[1]}, calculated in {@link
* #calculateExtraLayoutSpace}.
*/
private void recycleViewsFromEnd(RecyclerView.Recycler recycler, int scrollingOffset,
int noRecycleSpace) {
final int childCount = getChildCount();
if (scrollingOffset < 0) {
if (DEBUG) {
Log.d(TAG, "Called recycle from end with a negative value. This might happen"
+ " during layout changes but may be sign of a bug");
}
return;
}
final int limit = mOrientationHelper.getEnd() - scrollingOffset + noRecycleSpace;
if (mShouldReverseLayout) {
for (int i = 0; i < childCount; i++) {
View child = getChildAt(i);
if (mOrientationHelper.getDecoratedStart(child) < limit
|| mOrientationHelper.getTransformedStartWithDecoration(child) < limit) {
// stop here
recycleChildren(recycler, 0, i);
return;
}
}
} else {
for (int i = childCount - 1; i >= 0; i--) {
View child = getChildAt(i);
if (mOrientationHelper.getDecoratedStart(child) < limit
|| mOrientationHelper.getTransformedStartWithDecoration(child) < limit) {
// stop here
recycleChildren(recycler, childCount - 1, i);
return;
}
}
}
}
/**
* Helper method to call appropriate recycle method depending on current layout direction
*
* @param recycler Current recycler that is attached to RecyclerView
* @param layoutState Current layout state. Right now, this object does not change but
* we may consider moving it out of this view so passing around as a
* parameter for now, rather than accessing {@link #mLayoutState}
* @see #recycleViewsFromStart(RecyclerView.Recycler, int, int)
* @see #recycleViewsFromEnd(RecyclerView.Recycler, int, int)
* @see LinearLayoutManager.LayoutState#mLayoutDirection
*/
private void recycleByLayoutState(RecyclerView.Recycler recycler, LayoutState layoutState) {
if (!layoutState.mRecycle || layoutState.mInfinite) {
return;
}
int scrollingOffset = layoutState.mScrollingOffset;
int noRecycleSpace = layoutState.mNoRecycleSpace;
if (layoutState.mLayoutDirection == LayoutState.LAYOUT_START) {
recycleViewsFromEnd(recycler, scrollingOffset, noRecycleSpace);
} else {
recycleViewsFromStart(recycler, scrollingOffset, noRecycleSpace);
}
}
/**
* The magic functions :). Fills the given layout, defined by the layoutState. This is fairly
* independent from the rest of the {@link LinearLayoutManager}
* and with little change, can be made publicly available as a helper class.
*
* @param recycler Current recycler that is attached to RecyclerView
* @param layoutState Configuration on how we should fill out the available space.
* @param state Context passed by the RecyclerView to control scroll steps.
* @param stopOnFocusable If true, filling stops in the first focusable new child
* @return Number of pixels that it added. Useful for scroll functions.
*/
int fill(RecyclerView.Recycler recycler, LayoutState layoutState,
RecyclerView.State state, boolean stopOnFocusable) {
// max offset we should set is mFastScroll + available
final int start = layoutState.mAvailable;
if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
// TODO ugly bug fix. should not happen
if (layoutState.mAvailable < 0) {
layoutState.mScrollingOffset += layoutState.mAvailable;
}
recycleByLayoutState(recycler, layoutState);
}
int remainingSpace = layoutState.mAvailable + layoutState.mExtraFillSpace;
LayoutChunkResult layoutChunkResult = mLayoutChunkResult;
while ((layoutState.mInfinite || remainingSpace > 0) && layoutState.hasMore(state)) {
layoutChunkResult.resetInternal();
if (RecyclerView.VERBOSE_TRACING) {
TraceCompat.beginSection("LLM LayoutChunk");
}
layoutChunk(recycler, state, layoutState, layoutChunkResult);
if (RecyclerView.VERBOSE_TRACING) {
TraceCompat.endSection();
}
if (layoutChunkResult.mFinished) {
break;
}
layoutState.mOffset += layoutChunkResult.mConsumed * layoutState.mLayoutDirection;
/**
* Consume the available space if:
* * layoutChunk did not request to be ignored
* * OR we are laying out scrap children
* * OR we are not doing pre-layout
*/
if (!layoutChunkResult.mIgnoreConsumed || layoutState.mScrapList != null
|| !state.isPreLayout()) {
layoutState.mAvailable -= layoutChunkResult.mConsumed;
// we keep a separate remaining space because mAvailable is important for recycling
remainingSpace -= layoutChunkResult.mConsumed;
}
if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
layoutState.mScrollingOffset += layoutChunkResult.mConsumed;
if (layoutState.mAvailable < 0) {
layoutState.mScrollingOffset += layoutState.mAvailable;
}
recycleByLayoutState(recycler, layoutState);
}
if (stopOnFocusable && layoutChunkResult.mFocusable) {
break;
}
}
if (DEBUG) {
validateChildOrder();
}
return start - layoutState.mAvailable;
}
void layoutChunk(RecyclerView.Recycler recycler, RecyclerView.State state,
LayoutState layoutState, LayoutChunkResult result) {
View view = layoutState.next(recycler);
if (view == null) {
if (DEBUG && layoutState.mScrapList == null) {
throw new RuntimeException("received null view when unexpected");
}
// if we are laying out views in scrap, this may return null which means there is
// no more items to layout.
result.mFinished = true;
return;
}
RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) view.getLayoutParams();
if (layoutState.mScrapList == null) {
if (mShouldReverseLayout == (layoutState.mLayoutDirection
== LayoutState.LAYOUT_START)) {
addView(view);
} else {
addView(view, 0);
}
} else {
if (mShouldReverseLayout == (layoutState.mLayoutDirection
== LayoutState.LAYOUT_START)) {
addDisappearingView(view);
} else {
addDisappearingView(view, 0);
}
}
measureChildWithMargins(view, 0, 0);
result.mConsumed = mOrientationHelper.getDecoratedMeasurement(view);
int left, top, right, bottom;
if (mOrientation == VERTICAL) {
if (isLayoutRTL()) {
right = getWidth() - getPaddingRight();
left = right - mOrientationHelper.getDecoratedMeasurementInOther(view);
} else {
left = getPaddingLeft();
right = left + mOrientationHelper.getDecoratedMeasurementInOther(view);
}
if (layoutState.mLayoutDirection == LayoutState.LAYOUT_START) {
bottom = layoutState.mOffset;
top = layoutState.mOffset - result.mConsumed;
} else {
top = layoutState.mOffset;
bottom = layoutState.mOffset + result.mConsumed;
}
} else {
top = getPaddingTop();
bottom = top + mOrientationHelper.getDecoratedMeasurementInOther(view);
if (layoutState.mLayoutDirection == LayoutState.LAYOUT_START) {
right = layoutState.mOffset;
left = layoutState.mOffset - result.mConsumed;
} else {
left = layoutState.mOffset;
right = layoutState.mOffset + result.mConsumed;
}
}
// We calculate everything with View's bounding box (which includes decor and margins)
// To calculate correct layout position, we subtract margins.
layoutDecoratedWithMargins(view, left, top, right, bottom);
if (DEBUG) {
Log.d(TAG, "laid out child at position " + getPosition(view) + ", with l:"
+ (left + params.leftMargin) + ", t:" + (top + params.topMargin) + ", r:"
+ (right - params.rightMargin) + ", b:" + (bottom - params.bottomMargin));
}
// Consume the available space if the view is not removed OR changed
if (params.isItemRemoved() || params.isItemChanged()) {
result.mIgnoreConsumed = true;
}
result.mFocusable = view.hasFocusable();
}
@Override
boolean shouldMeasureTwice() {
return getHeightMode() != View.MeasureSpec.EXACTLY
&& getWidthMode() != View.MeasureSpec.EXACTLY
&& hasFlexibleChildInBothOrientations();
}
/**
* Converts a focusDirection to orientation.
*
* @param focusDirection One of {@link View#FOCUS_UP}, {@link View#FOCUS_DOWN},
* {@link View#FOCUS_LEFT}, {@link View#FOCUS_RIGHT},
* {@link View#FOCUS_BACKWARD}, {@link View#FOCUS_FORWARD}
* or 0 for not applicable
* @return {@link LayoutState#LAYOUT_START} or {@link LayoutState#LAYOUT_END} if focus direction
* is applicable to current state, {@link LayoutState#INVALID_LAYOUT} otherwise.
*/
int convertFocusDirectionToLayoutDirection(int focusDirection) {
switch (focusDirection) {
case View.FOCUS_BACKWARD:
if (mOrientation == VERTICAL) {
return LayoutState.LAYOUT_START;
} else if (isLayoutRTL()) {
return LayoutState.LAYOUT_END;
} else {
return LayoutState.LAYOUT_START;
}
case View.FOCUS_FORWARD:
if (mOrientation == VERTICAL) {
return LayoutState.LAYOUT_END;
} else if (isLayoutRTL()) {
return LayoutState.LAYOUT_START;
} else {
return LayoutState.LAYOUT_END;
}
case View.FOCUS_UP:
return mOrientation == VERTICAL ? LayoutState.LAYOUT_START
: LayoutState.INVALID_LAYOUT;
case View.FOCUS_DOWN:
return mOrientation == VERTICAL ? LayoutState.LAYOUT_END
: LayoutState.INVALID_LAYOUT;
case View.FOCUS_LEFT:
return mOrientation == HORIZONTAL ? LayoutState.LAYOUT_START
: LayoutState.INVALID_LAYOUT;
case View.FOCUS_RIGHT:
return mOrientation == HORIZONTAL ? LayoutState.LAYOUT_END
: LayoutState.INVALID_LAYOUT;
default:
if (DEBUG) {
Log.d(TAG, "Unknown focus request:" + focusDirection);
}
return LayoutState.INVALID_LAYOUT;
}
}
/**
* Convenience method to find the child closes to start. Caller should check it has enough
* children.
*
* @return The child closes to start of the layout from user's perspective.
*/
private View getChildClosestToStart() {
return getChildAt(mShouldReverseLayout ? getChildCount() - 1 : 0);
}
/**
* Convenience method to find the child closes to end. Caller should check it has enough
* children.
*
* @return The child closes to end of the layout from user's perspective.
*/
private View getChildClosestToEnd() {
return getChildAt(mShouldReverseLayout ? 0 : getChildCount() - 1);
}
/**
* Convenience method to find the visible child closes to start. Caller should check if it has
* enough children.
*
* @param completelyVisible Whether child should be completely visible or not
* @return The first visible child closest to start of the layout from user's perspective.
*/
View findFirstVisibleChildClosestToStart(boolean completelyVisible,
boolean acceptPartiallyVisible) {
if (mShouldReverseLayout) {
return findOneVisibleChild(getChildCount() - 1, -1, completelyVisible,
acceptPartiallyVisible);
} else {
return findOneVisibleChild(0, getChildCount(), completelyVisible,
acceptPartiallyVisible);
}
}
/**
* Convenience method to find the visible child closes to end. Caller should check if it has
* enough children.
*
* @param completelyVisible Whether child should be completely visible or not
* @return The first visible child closest to end of the layout from user's perspective.
*/
View findFirstVisibleChildClosestToEnd(boolean completelyVisible,
boolean acceptPartiallyVisible) {
if (mShouldReverseLayout) {
return findOneVisibleChild(0, getChildCount(), completelyVisible,
acceptPartiallyVisible);
} else {
return findOneVisibleChild(getChildCount() - 1, -1, completelyVisible,
acceptPartiallyVisible);
}
}
/**
* Among the children that are suitable to be considered as an anchor child, returns the one
* closest to the end of the layout.
* <p>
* Due to ambiguous adapter updates or children being removed, some children's positions may be
* invalid. This method is a best effort to find a position within adapter bounds if possible.
* <p>
* It also prioritizes children that are within the visible bounds.
* @return A View that can be used an an anchor View.
*/
private View findReferenceChildClosestToEnd(RecyclerView.Recycler recycler,
RecyclerView.State state) {
return mShouldReverseLayout ? findFirstReferenceChild(recycler, state) :
findLastReferenceChild(recycler, state);
}
/**
* Among the children that are suitable to be considered as an anchor child, returns the one
* closest to the start of the layout.
* <p>
* Due to ambiguous adapter updates or children being removed, some children's positions may be
* invalid. This method is a best effort to find a position within adapter bounds if possible.
* <p>
* It also prioritizes children that are within the visible bounds.
*
* @return A View that can be used an an anchor View.
*/
private View findReferenceChildClosestToStart(RecyclerView.Recycler recycler,
RecyclerView.State state) {
return mShouldReverseLayout ? findLastReferenceChild(recycler, state) :
findFirstReferenceChild(recycler, state);
}
private View findFirstReferenceChild(RecyclerView.Recycler recycler, RecyclerView.State state) {
return findReferenceChild(recycler, state, 0, getChildCount(), state.getItemCount());
}
private View findLastReferenceChild(RecyclerView.Recycler recycler, RecyclerView.State state) {
return findReferenceChild(recycler, state, getChildCount() - 1, -1, state.getItemCount());
}
// overridden by GridLayoutManager
View findReferenceChild(RecyclerView.Recycler recycler, RecyclerView.State state,
int start, int end, int itemCount) {
ensureLayoutState();
View invalidMatch = null;
View outOfBoundsMatch = null;
final int boundsStart = mOrientationHelper.getStartAfterPadding();
final int boundsEnd = mOrientationHelper.getEndAfterPadding();
final int diff = end > start ? 1 : -1;
for (int i = start; i != end; i += diff) {
final View view = getChildAt(i);
final int position = getPosition(view);
final int childStart = mOrientationHelper.getDecoratedStart(view);
final int childEnd = mOrientationHelper.getDecoratedEnd(view);
if (position >= 0 && position < itemCount) {
if (((RecyclerView.LayoutParams) view.getLayoutParams()).isItemRemoved()) {
if (invalidMatch == null) {
invalidMatch = view; // removed item, least preferred
}
} else {
// b/148869110: usually if childStart >= boundsEnd the child is out of
// bounds, except if the child is 0 pixels!
if ((childStart >= boundsEnd && childEnd > boundsEnd)
|| (childEnd <= boundsStart && childStart < boundsStart)) {
// item is not visible, less preferred
if (outOfBoundsMatch == null) {
outOfBoundsMatch = view;
}
} else {
return view;
}
}
}
}
return outOfBoundsMatch != null ? outOfBoundsMatch : invalidMatch;
}
// returns the out-of-bound child view closest to RV's end bounds. An out-of-bound child is
// defined as a child that's either partially or fully invisible (outside RV's padding area).
private View findPartiallyOrCompletelyInvisibleChildClosestToEnd() {
return mShouldReverseLayout ? findFirstPartiallyOrCompletelyInvisibleChild()
: findLastPartiallyOrCompletelyInvisibleChild();
}
// returns the out-of-bound child view closest to RV's starting bounds. An out-of-bound child is
// defined as a child that's either partially or fully invisible (outside RV's padding area).
private View findPartiallyOrCompletelyInvisibleChildClosestToStart() {
return mShouldReverseLayout ? findLastPartiallyOrCompletelyInvisibleChild() :
findFirstPartiallyOrCompletelyInvisibleChild();
}
private View findFirstPartiallyOrCompletelyInvisibleChild() {
return findOnePartiallyOrCompletelyInvisibleChild(0, getChildCount());
}
private View findLastPartiallyOrCompletelyInvisibleChild() {
return findOnePartiallyOrCompletelyInvisibleChild(getChildCount() - 1, -1);
}
/**
* Returns the adapter position of the first visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
* <p>
* Note that, this value is not affected by layout orientation or item order traversal.
* ({@link #setReverseLayout(boolean)}). Views are sorted by their positions in the adapter,
* not in the layout.
* <p>
* If RecyclerView has item decorators, they will be considered in calculations as well.
* <p>
* LayoutManager may pre-cache some views that are not necessarily visible. Those views
* are ignored in this method.
*
* @return The adapter position of the first visible item or {@link RecyclerView#NO_POSITION} if
* there aren't any visible items.
* @see #findFirstCompletelyVisibleItemPosition()
* @see #findLastVisibleItemPosition()
*/
public int findFirstVisibleItemPosition() {
final View child = findOneVisibleChild(0, getChildCount(), false, true);
return child == null ? RecyclerView.NO_POSITION : getPosition(child);
}
/**
* Returns the adapter position of the first fully visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
* <p>
* Note that bounds check is only performed in the current orientation. That means, if
* LayoutManager is horizontal, it will only check the view's left and right edges.
*
* @return The adapter position of the first fully visible item or
* {@link RecyclerView#NO_POSITION} if there aren't any visible items.
* @see #findFirstVisibleItemPosition()
* @see #findLastCompletelyVisibleItemPosition()
*/
public int findFirstCompletelyVisibleItemPosition() {
final View child = findOneVisibleChild(0, getChildCount(), true, false);
return child == null ? RecyclerView.NO_POSITION : getPosition(child);
}
/**
* Returns the adapter position of the last visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
* <p>
* Note that, this value is not affected by layout orientation or item order traversal.
* ({@link #setReverseLayout(boolean)}). Views are sorted by their positions in the adapter,
* not in the layout.
* <p>
* If RecyclerView has item decorators, they will be considered in calculations as well.
* <p>
* LayoutManager may pre-cache some views that are not necessarily visible. Those views
* are ignored in this method.
*
* @return The adapter position of the last visible view or {@link RecyclerView#NO_POSITION} if
* there aren't any visible items.
* @see #findLastCompletelyVisibleItemPosition()
* @see #findFirstVisibleItemPosition()
*/
public int findLastVisibleItemPosition() {
final View child = findOneVisibleChild(getChildCount() - 1, -1, false, true);
return child == null ? RecyclerView.NO_POSITION : getPosition(child);
}
/**
* Returns the adapter position of the last fully visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
* <p>
* Note that bounds check is only performed in the current orientation. That means, if
* LayoutManager is horizontal, it will only check the view's left and right edges.
*
* @return The adapter position of the last fully visible view or
* {@link RecyclerView#NO_POSITION} if there aren't any visible items.
* @see #findLastVisibleItemPosition()
* @see #findFirstCompletelyVisibleItemPosition()
*/
public int findLastCompletelyVisibleItemPosition() {
final View child = findOneVisibleChild(getChildCount() - 1, -1, true, false);
return child == null ? RecyclerView.NO_POSITION : getPosition(child);
}
// Returns the first child that is visible in the provided index range, i.e. either partially or
// fully visible depending on the arguments provided. Completely invisible children are not
// acceptable by this method, but could be returned
// using #findOnePartiallyOrCompletelyInvisibleChild
View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
boolean acceptPartiallyVisible) {
ensureLayoutState();
@ViewBoundsCheck.ViewBounds int preferredBoundsFlag = 0;
@ViewBoundsCheck.ViewBounds int acceptableBoundsFlag = 0;
if (completelyVisible) {
preferredBoundsFlag = (ViewBoundsCheck.FLAG_CVS_GT_PVS | ViewBoundsCheck.FLAG_CVS_EQ_PVS
| ViewBoundsCheck.FLAG_CVE_LT_PVE | ViewBoundsCheck.FLAG_CVE_EQ_PVE);
} else {
preferredBoundsFlag = (ViewBoundsCheck.FLAG_CVS_LT_PVE
| ViewBoundsCheck.FLAG_CVE_GT_PVS);
}
if (acceptPartiallyVisible) {
acceptableBoundsFlag = (ViewBoundsCheck.FLAG_CVS_LT_PVE
| ViewBoundsCheck.FLAG_CVE_GT_PVS);
}
return (mOrientation == HORIZONTAL) ? mHorizontalBoundCheck
.findOneViewWithinBoundFlags(fromIndex, toIndex, preferredBoundsFlag,
acceptableBoundsFlag) : mVerticalBoundCheck
.findOneViewWithinBoundFlags(fromIndex, toIndex, preferredBoundsFlag,
acceptableBoundsFlag);
}
View findOnePartiallyOrCompletelyInvisibleChild(int fromIndex, int toIndex) {
ensureLayoutState();
final int next = toIndex > fromIndex ? 1 : (toIndex < fromIndex ? -1 : 0);
if (next == 0) {
return getChildAt(fromIndex);
}
@ViewBoundsCheck.ViewBounds int preferredBoundsFlag = 0;
@ViewBoundsCheck.ViewBounds int acceptableBoundsFlag = 0;
if (mOrientationHelper.getDecoratedStart(getChildAt(fromIndex))
< mOrientationHelper.getStartAfterPadding()) {
preferredBoundsFlag = (ViewBoundsCheck.FLAG_CVS_LT_PVS | ViewBoundsCheck.FLAG_CVE_LT_PVE
| ViewBoundsCheck.FLAG_CVE_GT_PVS);
acceptableBoundsFlag = (ViewBoundsCheck.FLAG_CVS_LT_PVS
| ViewBoundsCheck.FLAG_CVE_LT_PVE);
} else {
preferredBoundsFlag = (ViewBoundsCheck.FLAG_CVE_GT_PVE | ViewBoundsCheck.FLAG_CVS_GT_PVS
| ViewBoundsCheck.FLAG_CVS_LT_PVE);
acceptableBoundsFlag = (ViewBoundsCheck.FLAG_CVE_GT_PVE
| ViewBoundsCheck.FLAG_CVS_GT_PVS);
}
return (mOrientation == HORIZONTAL) ? mHorizontalBoundCheck
.findOneViewWithinBoundFlags(fromIndex, toIndex, preferredBoundsFlag,
acceptableBoundsFlag) : mVerticalBoundCheck
.findOneViewWithinBoundFlags(fromIndex, toIndex, preferredBoundsFlag,
acceptableBoundsFlag);
}
@Override
public View onFocusSearchFailed(View focused, int focusDirection,
RecyclerView.Recycler recycler, RecyclerView.State state) {
resolveShouldLayoutReverse();
if (getChildCount() == 0) {
return null;
}
final int layoutDir = convertFocusDirectionToLayoutDirection(focusDirection);
if (layoutDir == LayoutState.INVALID_LAYOUT) {
return null;
}
ensureLayoutState();
final int maxScroll = (int) (MAX_SCROLL_FACTOR * mOrientationHelper.getTotalSpace());
updateLayoutState(layoutDir, maxScroll, false, state);
mLayoutState.mScrollingOffset = LayoutState.SCROLLING_OFFSET_NaN;
mLayoutState.mRecycle = false;
fill(recycler, mLayoutState, state, true);
// nextCandidate is the first child view in the layout direction that's partially
// within RV's bounds, i.e. part of it is visible or it's completely invisible but still
// touching RV's bounds. This will be the unfocusable candidate view to become visible onto
// the screen if no focusable views are found in the given layout direction.
final View nextCandidate;
if (layoutDir == LayoutState.LAYOUT_START) {
nextCandidate = findPartiallyOrCompletelyInvisibleChildClosestToStart();
} else {
nextCandidate = findPartiallyOrCompletelyInvisibleChildClosestToEnd();
}
// nextFocus is meaningful only if it refers to a focusable child, in which case it
// indicates the next view to gain focus.
final View nextFocus;
if (layoutDir == LayoutState.LAYOUT_START) {
nextFocus = getChildClosestToStart();
} else {
nextFocus = getChildClosestToEnd();
}
if (nextFocus.hasFocusable()) {
if (nextCandidate == null) {
return null;
}
return nextFocus;
}
return nextCandidate;
}
/**
* Used for debugging.
* Logs the internal representation of children to default logger.
*/
private void logChildren() {
Log.d(TAG, "internal representation of views on the screen");
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
Log.d(TAG, "item " + getPosition(child) + ", coord:"
+ mOrientationHelper.getDecoratedStart(child));
}
Log.d(TAG, "==============");
}
/**
* Used for debugging.
* Validates that child views are laid out in correct order. This is important because rest of
* the algorithm relies on this constraint.
*
* In default layout, child 0 should be closest to screen position 0 and last child should be
* closest to position WIDTH or HEIGHT.
* In reverse layout, last child should be closes to screen position 0 and first child should
* be closest to position WIDTH or HEIGHT
*/
void validateChildOrder() {
Log.d(TAG, "validating child count " + getChildCount());
if (getChildCount() < 1) {
return;
}
int lastPos = getPosition(getChildAt(0));
int lastScreenLoc = mOrientationHelper.getDecoratedStart(getChildAt(0));
if (mShouldReverseLayout) {
for (int i = 1; i < getChildCount(); i++) {
View child = getChildAt(i);
int pos = getPosition(child);
int screenLoc = mOrientationHelper.getDecoratedStart(child);
if (pos < lastPos) {
logChildren();
throw new RuntimeException("detected invalid position. loc invalid? "
+ (screenLoc < lastScreenLoc));
}
if (screenLoc > lastScreenLoc) {
logChildren();
throw new RuntimeException("detected invalid location");
}
}
} else {
for (int i = 1; i < getChildCount(); i++) {
View child = getChildAt(i);
int pos = getPosition(child);
int screenLoc = mOrientationHelper.getDecoratedStart(child);
if (pos < lastPos) {
logChildren();
throw new RuntimeException("detected invalid position. loc invalid? "
+ (screenLoc < lastScreenLoc));
}
if (screenLoc < lastScreenLoc) {
logChildren();
throw new RuntimeException("detected invalid location");
}
}
}
}
@Override
public boolean supportsPredictiveItemAnimations() {
return mPendingSavedState == null && mLastStackFromEnd == mStackFromEnd;
}
/**
* {@inheritDoc}
*/
// This method is only intended to be called (and should only ever be called) by
// ItemTouchHelper.
@Override
public void prepareForDrop(@NonNull View view, @NonNull View target, int x, int y) {
assertNotInLayoutOrScroll("Cannot drop a view during a scroll or layout calculation");
ensureLayoutState();
resolveShouldLayoutReverse();
final int myPos = getPosition(view);
final int targetPos = getPosition(target);
final int dropDirection = myPos < targetPos ? LayoutState.ITEM_DIRECTION_TAIL
: LayoutState.ITEM_DIRECTION_HEAD;
if (mShouldReverseLayout) {
if (dropDirection == LayoutState.ITEM_DIRECTION_TAIL) {
scrollToPositionWithOffset(targetPos,
mOrientationHelper.getEndAfterPadding()
- (mOrientationHelper.getDecoratedStart(target)
+ mOrientationHelper.getDecoratedMeasurement(view)));
} else {
scrollToPositionWithOffset(targetPos,
mOrientationHelper.getEndAfterPadding()
- mOrientationHelper.getDecoratedEnd(target));
}
} else {
if (dropDirection == LayoutState.ITEM_DIRECTION_HEAD) {
scrollToPositionWithOffset(targetPos, mOrientationHelper.getDecoratedStart(target));
} else {
scrollToPositionWithOffset(targetPos,
mOrientationHelper.getDecoratedEnd(target)
- mOrientationHelper.getDecoratedMeasurement(view));
}
}
}
/**
* Helper class that keeps temporary state while {LayoutManager} is filling out the empty
* space.
*/
static class LayoutState {
static final String TAG = "LLM#LayoutState";
static final int LAYOUT_START = -1;
static final int LAYOUT_END = 1;
static final int INVALID_LAYOUT = Integer.MIN_VALUE;
static final int ITEM_DIRECTION_HEAD = -1;
static final int ITEM_DIRECTION_TAIL = 1;
static final int SCROLLING_OFFSET_NaN = Integer.MIN_VALUE;
/**
* We may not want to recycle children in some cases (e.g. layout)
*/
boolean mRecycle = true;
/**
* Pixel offset where layout should start
*/
int mOffset;
/**
* Number of pixels that we should fill, in the layout direction.
*/
int mAvailable;
/**
* Current position on the adapter to get the next item.
*/
int mCurrentPosition;
/**
* Defines the direction in which the data adapter is traversed.
* Should be {@link #ITEM_DIRECTION_HEAD} or {@link #ITEM_DIRECTION_TAIL}
*/
int mItemDirection;
/**
* Defines the direction in which the layout is filled.
* Should be {@link #LAYOUT_START} or {@link #LAYOUT_END}
*/
int mLayoutDirection;
/**
* Used when LayoutState is constructed in a scrolling state.
* It should be set the amount of scrolling we can make without creating a new view.
* Settings this is required for efficient view recycling.
*/
int mScrollingOffset;
/**
* Used if you want to pre-layout items that are not yet visible.
* The difference with {@link #mAvailable} is that, when recycling, distance laid out for
* {@link #mExtraFillSpace} is not considered to avoid recycling visible children.
*/
int mExtraFillSpace = 0;
/**
* Contains the {@link #calculateExtraLayoutSpace(RecyclerView.State, int[])} extra layout
* space} that should be excluded for recycling when cleaning up the tail of the list during
* a smooth scroll.
*/
int mNoRecycleSpace = 0;
/**
* Equal to {@link RecyclerView.State#isPreLayout()}. When consuming scrap, if this value
* is set to true, we skip removed views since they should not be laid out in post layout
* step.
*/
boolean mIsPreLayout = false;
/**
* The most recent {@link #scrollBy(int, RecyclerView.Recycler, RecyclerView.State)}
* amount.
*/
int mLastScrollDelta;
/**
* When LLM needs to layout particular views, it sets this list in which case, LayoutState
* will only return views from this list and return null if it cannot find an item.
*/
List<RecyclerView.ViewHolder> mScrapList = null;
/**
* Used when there is no limit in how many views can be laid out.
*/
boolean mInfinite;
/**
* @return true if there are more items in the data adapter
*/
boolean hasMore(RecyclerView.State state) {
return mCurrentPosition >= 0 && mCurrentPosition < state.getItemCount();
}
/**
* Gets the view for the next element that we should layout.
* Also updates current item index to the next item, based on {@link #mItemDirection}
*
* @return The next element that we should layout.
*/
View next(RecyclerView.Recycler recycler) {
if (mScrapList != null) {
return nextViewFromScrapList();
}
final View view = recycler.getViewForPosition(mCurrentPosition);
mCurrentPosition += mItemDirection;
return view;
}
/**
* Returns the next item from the scrap list.
* <p>
* Upon finding a valid VH, sets current item position to VH.itemPosition + mItemDirection
*
* @return View if an item in the current position or direction exists if not null.
*/
private View nextViewFromScrapList() {
final int size = mScrapList.size();
for (int i = 0; i < size; i++) {
final View view = mScrapList.get(i).itemView;
final RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) view.getLayoutParams();
if (lp.isItemRemoved()) {
continue;
}
if (mCurrentPosition == lp.getViewLayoutPosition()) {
assignPositionFromScrapList(view);
return view;
}
}
return null;
}
public void assignPositionFromScrapList() {
assignPositionFromScrapList(null);
}
public void assignPositionFromScrapList(View ignore) {
final View closest = nextViewInLimitedList(ignore);
if (closest == null) {
mCurrentPosition = RecyclerView.NO_POSITION;
} else {
mCurrentPosition = ((RecyclerView.LayoutParams) closest.getLayoutParams())
.getViewLayoutPosition();
}
}
public View nextViewInLimitedList(View ignore) {
int size = mScrapList.size();
View closest = null;
int closestDistance = Integer.MAX_VALUE;
if (DEBUG && mIsPreLayout) {
throw new IllegalStateException("Scrap list cannot be used in pre layout");
}
for (int i = 0; i < size; i++) {
View view = mScrapList.get(i).itemView;
final RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) view.getLayoutParams();
if (view == ignore || lp.isItemRemoved()) {
continue;
}
final int distance = (lp.getViewLayoutPosition() - mCurrentPosition)
* mItemDirection;
if (distance < 0) {
continue; // item is not in current direction
}
if (distance < closestDistance) {
closest = view;
closestDistance = distance;
if (distance == 0) {
break;
}
}
}
return closest;
}
void log() {
Log.d(TAG, "avail:" + mAvailable + ", ind:" + mCurrentPosition + ", dir:"
+ mItemDirection + ", offset:" + mOffset + ", layoutDir:" + mLayoutDirection);
}
}
/**
* @hide
*/
@RestrictTo(LIBRARY)
@SuppressLint("BanParcelableUsage")
public static class SavedState implements Parcelable {
int mAnchorPosition;
int mAnchorOffset;
boolean mAnchorLayoutFromEnd;
public SavedState() {
}
SavedState(Parcel in) {
mAnchorPosition = in.readInt();
mAnchorOffset = in.readInt();
mAnchorLayoutFromEnd = in.readInt() == 1;
}
public SavedState(SavedState other) {
mAnchorPosition = other.mAnchorPosition;
mAnchorOffset = other.mAnchorOffset;
mAnchorLayoutFromEnd = other.mAnchorLayoutFromEnd;
}
boolean hasValidAnchor() {
return mAnchorPosition >= 0;
}
void invalidateAnchor() {
mAnchorPosition = RecyclerView.NO_POSITION;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(mAnchorPosition);
dest.writeInt(mAnchorOffset);
dest.writeInt(mAnchorLayoutFromEnd ? 1 : 0);
}
public static final Parcelable.Creator<SavedState> CREATOR =
new Parcelable.Creator<SavedState>() {
@Override
public SavedState createFromParcel(Parcel in) {
return new SavedState(in);
}
@Override
public SavedState[] newArray(int size) {
return new SavedState[size];
}
};
}
/**
* Simple data class to keep Anchor information
*/
static class AnchorInfo {
OrientationHelper mOrientationHelper;
int mPosition;
int mCoordinate;
boolean mLayoutFromEnd;
boolean mValid;
AnchorInfo() {
reset();
}
void reset() {
mPosition = RecyclerView.NO_POSITION;
mCoordinate = INVALID_OFFSET;
mLayoutFromEnd = false;
mValid = false;
}
/**
* assigns anchor coordinate from the RecyclerView's padding depending on current
* layoutFromEnd value
*/
void assignCoordinateFromPadding() {
mCoordinate = mLayoutFromEnd
? mOrientationHelper.getEndAfterPadding()
: mOrientationHelper.getStartAfterPadding();
}
@Override
public String toString() {
return "AnchorInfo{"
+ "mPosition=" + mPosition
+ ", mCoordinate=" + mCoordinate
+ ", mLayoutFromEnd=" + mLayoutFromEnd
+ ", mValid=" + mValid
+ '}';
}
boolean isViewValidAsAnchor(View child, RecyclerView.State state) {
RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) child.getLayoutParams();
return !lp.isItemRemoved() && lp.getViewLayoutPosition() >= 0
&& lp.getViewLayoutPosition() < state.getItemCount();
}
public void assignFromViewAndKeepVisibleRect(View child, int position) {
final int spaceChange = mOrientationHelper.getTotalSpaceChange();
if (spaceChange >= 0) {
assignFromView(child, position);
return;
}
mPosition = position;
if (mLayoutFromEnd) {
final int prevLayoutEnd = mOrientationHelper.getEndAfterPadding() - spaceChange;
final int childEnd = mOrientationHelper.getDecoratedEnd(child);
final int previousEndMargin = prevLayoutEnd - childEnd;
mCoordinate = mOrientationHelper.getEndAfterPadding() - previousEndMargin;
// ensure we did not push child's top out of bounds because of this
if (previousEndMargin > 0) { // we have room to shift bottom if necessary
final int childSize = mOrientationHelper.getDecoratedMeasurement(child);
final int estimatedChildStart = mCoordinate - childSize;
final int layoutStart = mOrientationHelper.getStartAfterPadding();
final int previousStartMargin = mOrientationHelper.getDecoratedStart(child)
- layoutStart;
final int startReference = layoutStart + Math.min(previousStartMargin, 0);
final int startMargin = estimatedChildStart - startReference;
if (startMargin < 0) {
// offset to make top visible but not too much
mCoordinate += Math.min(previousEndMargin, -startMargin);
}
}
} else {
final int childStart = mOrientationHelper.getDecoratedStart(child);
final int startMargin = childStart - mOrientationHelper.getStartAfterPadding();
mCoordinate = childStart;
if (startMargin > 0) { // we have room to fix end as well
final int estimatedEnd = childStart
+ mOrientationHelper.getDecoratedMeasurement(child);
final int previousLayoutEnd = mOrientationHelper.getEndAfterPadding()
- spaceChange;
final int previousEndMargin = previousLayoutEnd
- mOrientationHelper.getDecoratedEnd(child);
final int endReference = mOrientationHelper.getEndAfterPadding()
- Math.min(0, previousEndMargin);
final int endMargin = endReference - estimatedEnd;
if (endMargin < 0) {
mCoordinate -= Math.min(startMargin, -endMargin);
}
}
}
}
public void assignFromView(View child, int position) {
if (mLayoutFromEnd) {
mCoordinate = mOrientationHelper.getDecoratedEnd(child)
+ mOrientationHelper.getTotalSpaceChange();
} else {
mCoordinate = mOrientationHelper.getDecoratedStart(child);
}
mPosition = position;
}
}
protected static class LayoutChunkResult {
public int mConsumed;
public boolean mFinished;
public boolean mIgnoreConsumed;
public boolean mFocusable;
void resetInternal() {
mConsumed = 0;
mFinished = false;
mIgnoreConsumed = false;
mFocusable = false;
}
}
}