src/com/android/launcher3/views/StickyHeaderLayout.java - platform/packages/apps/Launcher3 - Git at Google

 /*
  * Copyright (C) 2021 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 com.android.launcher3.views;

 import static android.view.View.MeasureSpec.EXACTLY;
 import static android.view.View.MeasureSpec.makeMeasureSpec;

 import static com.android.launcher3.anim.AnimatorListeners.forEndCallback;

 import android.animation.Animator;
 import android.animation.ObjectAnimator;
 import android.content.Context;
 import android.content.res.TypedArray;
 import android.util.AttributeSet;
 import android.util.FloatProperty;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.LinearLayout;

 import androidx.annotation.NonNull;
 import androidx.recyclerview.widget.RecyclerView;

 import com.android.launcher3.R;

 /**
  * A {@link LinearLayout} container which allows scrolling parts of its content based on the
  * scroll of a different view. Views which are marked as sticky are not scrolled, giving the
  * illusion of a sticky header.
  */
 public class StickyHeaderLayout extends LinearLayout implements
         RecyclerView.OnChildAttachStateChangeListener {

     private static final FloatProperty<StickyHeaderLayout> SCROLL_OFFSET =
             new FloatProperty<StickyHeaderLayout>("scrollAnimOffset") {
                 @Override
                 public void setValue(StickyHeaderLayout view, float offset) {
                     view.mScrollOffset = offset;
                     view.updateHeaderScroll();
                 }

                 @Override
                 public Float get(StickyHeaderLayout view) {
                     return view.mScrollOffset;
                 }
             };

     private static final MotionEventProxyMethod INTERCEPT_PROXY = ViewGroup::onInterceptTouchEvent;
     private static final MotionEventProxyMethod TOUCH_PROXY = ViewGroup::onTouchEvent;

     private RecyclerView mCurrentRecyclerView;
     private EmptySpaceView mCurrentEmptySpaceView;

     private float mLastScroll = 0;
     private float mScrollOffset = 0;
     private Animator mOffsetAnimator;

     private boolean mShouldForwardToRecyclerView = false;
     private int mHeaderHeight;

     public StickyHeaderLayout(Context context) {
         this(context, /* attrs= */ null);
     }

     public StickyHeaderLayout(Context context, AttributeSet attrs) {
         this(context, attrs, /* defStyleAttr= */ 0);
     }

     public StickyHeaderLayout(Context context, AttributeSet attrs, int defStyleAttr) {
         this(context, attrs, defStyleAttr, /* defStyleRes= */ 0);
     }

     public StickyHeaderLayout(Context context, AttributeSet attrs, int defStyleAttr,
             int defStyleRes) {
         super(context, attrs, defStyleAttr, defStyleRes);
     }

     /**
      * Sets the recycler view, this sticky header should track
      */
     public void setCurrentRecyclerView(RecyclerView currentRecyclerView) {
         boolean animateReset = mCurrentRecyclerView != null;
         if (mCurrentRecyclerView != null) {
             mCurrentRecyclerView.removeOnChildAttachStateChangeListener(this);
         }
         mCurrentRecyclerView = currentRecyclerView;
         mCurrentRecyclerView.addOnChildAttachStateChangeListener(this);
         findCurrentEmptyView();
         reset(animateReset);
     }

     public int getHeaderHeight() {
         return mHeaderHeight;
     }

     private void updateHeaderScroll() {
         mLastScroll = getCurrentScroll();
         int count = getChildCount();
         for (int i = 0; i < count; i++) {
             View child = getChildAt(i);
             MyLayoutParams lp = (MyLayoutParams) child.getLayoutParams();
             child.setTranslationY(Math.max(mLastScroll, lp.scrollLimit));
         }
     }

     private float getCurrentScroll() {
         return mScrollOffset + (mCurrentEmptySpaceView == null ? 0 : mCurrentEmptySpaceView.getY());
     }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec);

         mHeaderHeight = getMeasuredHeight();
         if (mCurrentEmptySpaceView != null) {
             mCurrentEmptySpaceView.setFixedHeight(mHeaderHeight);
         }
     }

     /** Resets any previous view translation. */
     public void reset(boolean animate) {
         if (mOffsetAnimator != null) {
             mOffsetAnimator.cancel();
             mOffsetAnimator = null;
         }

         mScrollOffset = 0;
         if (!animate) {
             updateHeaderScroll();
         } else {
             float startValue = mLastScroll - getCurrentScroll();
             mOffsetAnimator = ObjectAnimator.ofFloat(this, SCROLL_OFFSET, startValue, 0);
             mOffsetAnimator.addListener(forEndCallback(() -> mOffsetAnimator = null));
             mOffsetAnimator.start();
         }
     }

     @Override
     public boolean onInterceptTouchEvent(MotionEvent event) {
         return (mShouldForwardToRecyclerView = proxyMotionEvent(event, INTERCEPT_PROXY))
                 || super.onInterceptTouchEvent(event);
     }

     @Override
     public boolean onTouchEvent(MotionEvent event) {
         return mShouldForwardToRecyclerView && proxyMotionEvent(event, TOUCH_PROXY)
                 || super.onTouchEvent(event);
     }

     private boolean proxyMotionEvent(MotionEvent event, MotionEventProxyMethod method) {
         float dx = mCurrentRecyclerView.getLeft() - getLeft();
         float dy = mCurrentRecyclerView.getTop() - getTop();
         event.offsetLocation(dx, dy);
         try {
             return method.proxyEvent(mCurrentRecyclerView, event);
         } finally {
             event.offsetLocation(-dx, -dy);
         }
     }

     @Override
     public void onChildViewAttachedToWindow(@NonNull View view) {
         if (view instanceof EmptySpaceView) {
             findCurrentEmptyView();
         }
     }

     @Override
     public void onChildViewDetachedFromWindow(@NonNull View view) {
         if (view == mCurrentEmptySpaceView) {
             findCurrentEmptyView();
         }
     }

     private void findCurrentEmptyView() {
         if (mCurrentEmptySpaceView != null) {
             mCurrentEmptySpaceView.setOnYChangeCallback(null);
             mCurrentEmptySpaceView = null;
         }
         int childCount = mCurrentRecyclerView.getChildCount();
         for (int i = 0; i < childCount; i++) {
             View view = mCurrentRecyclerView.getChildAt(i);
             if (view instanceof EmptySpaceView) {
                 mCurrentEmptySpaceView = (EmptySpaceView) view;
                 mCurrentEmptySpaceView.setFixedHeight(getHeaderHeight());
                 mCurrentEmptySpaceView.setOnYChangeCallback(this::updateHeaderScroll);
                 return;
             }
         }
     }

     @Override
     protected void onLayout(boolean changed, int l, int t, int r, int b) {
         super.onLayout(changed, l, t, r, b);

         // Update various stick parameters
         int count = getChildCount();
         int stickyHeaderHeight = 0;
         for (int i = 0; i < count; i++) {
             View v = getChildAt(i);
             MyLayoutParams lp = (MyLayoutParams) v.getLayoutParams();
             if (lp.sticky) {
                 lp.scrollLimit = -v.getTop() + stickyHeaderHeight;
                 stickyHeaderHeight += v.getHeight();
             } else {
                 lp.scrollLimit = Integer.MIN_VALUE;
             }
         }
         updateHeaderScroll();
     }

     @Override
     protected LayoutParams generateDefaultLayoutParams() {
         return new MyLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
     }

     @Override
     protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp) {
         return new MyLayoutParams(lp.width, lp.height);
     }

     @Override
     public LayoutParams generateLayoutParams(AttributeSet attrs) {
         return new MyLayoutParams(getContext(), attrs);
     }

     @Override
     protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
         return p instanceof MyLayoutParams;
     }

     private static class MyLayoutParams extends LayoutParams {

         public final boolean sticky;
         public int scrollLimit;

         MyLayoutParams(int width, int height) {
             super(width, height);
             sticky = false;
         }

         MyLayoutParams(Context c, AttributeSet attrs) {
             super(c, attrs);
             TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.StickyScroller_Layout);
             sticky = a.getBoolean(R.styleable.StickyScroller_Layout_layout_sticky, false);
             a.recycle();
         }
     }

     private interface MotionEventProxyMethod {

         boolean proxyEvent(ViewGroup view, MotionEvent event);
     }

     /**
      * Empty view which allows listening for 'Y' changes
      */
     public static class EmptySpaceView extends View {

         private Runnable mOnYChangeCallback;
         private int mHeight = 0;

         public EmptySpaceView(Context context) {
             super(context);
             animate().setUpdateListener(v -> notifyYChanged());
         }

         /**
          * Sets the height for the empty view
          * @return true if the height changed, false otherwise
          */
         public boolean setFixedHeight(int height) {
             if (mHeight != height) {
                 mHeight = height;
                 requestLayout();
                 return true;
             }
             return false;
         }

         @Override
         protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
             super.onMeasure(widthMeasureSpec, makeMeasureSpec(mHeight, EXACTLY));
         }

         public void setOnYChangeCallback(Runnable callback) {
             mOnYChangeCallback = callback;
         }

         @Override
         protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
             super.onLayout(changed, left, top, right, bottom);
             notifyYChanged();
         }

         @Override
         public void offsetTopAndBottom(int offset) {
             super.offsetTopAndBottom(offset);
             notifyYChanged();
         }

         @Override
         public void setTranslationY(float translationY) {
             super.setTranslationY(translationY);
             notifyYChanged();
         }

         private void notifyYChanged() {
             if (mOnYChangeCallback != null) {
                 mOnYChangeCallback.run();
             }
         }
     }
 }
	/*
	* Copyright (C) 2021 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 com.android.launcher3.views;

	import static android.view.View.MeasureSpec.EXACTLY;
	import static android.view.View.MeasureSpec.makeMeasureSpec;

	import static com.android.launcher3.anim.AnimatorListeners.forEndCallback;

	import android.animation.Animator;
	import android.animation.ObjectAnimator;
	import android.content.Context;
	import android.content.res.TypedArray;
	import android.util.AttributeSet;
	import android.util.FloatProperty;
	import android.view.MotionEvent;
	import android.view.View;
	import android.view.ViewGroup;
	import android.widget.LinearLayout;

	import androidx.annotation.NonNull;
	import androidx.recyclerview.widget.RecyclerView;

	import com.android.launcher3.R;

	/**
	* A {@link LinearLayout} container which allows scrolling parts of its content based on the
	* scroll of a different view. Views which are marked as sticky are not scrolled, giving the
	* illusion of a sticky header.
	*/
	public class StickyHeaderLayout extends LinearLayout implements
	RecyclerView.OnChildAttachStateChangeListener {

	private static final FloatProperty<StickyHeaderLayout> SCROLL_OFFSET =
	new FloatProperty<StickyHeaderLayout>("scrollAnimOffset") {
	@Override
	public void setValue(StickyHeaderLayout view, float offset) {
	view.mScrollOffset = offset;
	view.updateHeaderScroll();
	}

	@Override
	public Float get(StickyHeaderLayout view) {
	return view.mScrollOffset;
	}
	};

	private static final MotionEventProxyMethod INTERCEPT_PROXY = ViewGroup::onInterceptTouchEvent;
	private static final MotionEventProxyMethod TOUCH_PROXY = ViewGroup::onTouchEvent;

	private RecyclerView mCurrentRecyclerView;
	private EmptySpaceView mCurrentEmptySpaceView;

	private float mLastScroll = 0;
	private float mScrollOffset = 0;
	private Animator mOffsetAnimator;

	private boolean mShouldForwardToRecyclerView = false;
	private int mHeaderHeight;

	public StickyHeaderLayout(Context context) {
	this(context, /* attrs= */ null);
	}

	public StickyHeaderLayout(Context context, AttributeSet attrs) {
	this(context, attrs, /* defStyleAttr= */ 0);
	}

	public StickyHeaderLayout(Context context, AttributeSet attrs, int defStyleAttr) {
	this(context, attrs, defStyleAttr, /* defStyleRes= */ 0);
	}

	public StickyHeaderLayout(Context context, AttributeSet attrs, int defStyleAttr,
	int defStyleRes) {
	super(context, attrs, defStyleAttr, defStyleRes);
	}

	/**
	* Sets the recycler view, this sticky header should track
	*/
	public void setCurrentRecyclerView(RecyclerView currentRecyclerView) {
	boolean animateReset = mCurrentRecyclerView != null;
	if (mCurrentRecyclerView != null) {
	mCurrentRecyclerView.removeOnChildAttachStateChangeListener(this);
	}
	mCurrentRecyclerView = currentRecyclerView;
	mCurrentRecyclerView.addOnChildAttachStateChangeListener(this);
	findCurrentEmptyView();
	reset(animateReset);
	}

	public int getHeaderHeight() {
	return mHeaderHeight;
	}

	private void updateHeaderScroll() {
	mLastScroll = getCurrentScroll();
	int count = getChildCount();
	for (int i = 0; i < count; i++) {
	View child = getChildAt(i);
	MyLayoutParams lp = (MyLayoutParams) child.getLayoutParams();
	child.setTranslationY(Math.max(mLastScroll, lp.scrollLimit));
	}
	}

	private float getCurrentScroll() {
	return mScrollOffset + (mCurrentEmptySpaceView == null ? 0 : mCurrentEmptySpaceView.getY());
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	super.onMeasure(widthMeasureSpec, heightMeasureSpec);

	mHeaderHeight = getMeasuredHeight();
	if (mCurrentEmptySpaceView != null) {
	mCurrentEmptySpaceView.setFixedHeight(mHeaderHeight);
	}
	}

	/** Resets any previous view translation. */
	public void reset(boolean animate) {
	if (mOffsetAnimator != null) {
	mOffsetAnimator.cancel();
	mOffsetAnimator = null;
	}

	mScrollOffset = 0;
	if (!animate) {
	updateHeaderScroll();
	} else {
	float startValue = mLastScroll - getCurrentScroll();
	mOffsetAnimator = ObjectAnimator.ofFloat(this, SCROLL_OFFSET, startValue, 0);
	mOffsetAnimator.addListener(forEndCallback(() -> mOffsetAnimator = null));
	mOffsetAnimator.start();
	}
	}

	@Override
	public boolean onInterceptTouchEvent(MotionEvent event) {
	return (mShouldForwardToRecyclerView = proxyMotionEvent(event, INTERCEPT_PROXY))
	\|\| super.onInterceptTouchEvent(event);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
	return mShouldForwardToRecyclerView && proxyMotionEvent(event, TOUCH_PROXY)
	\|\| super.onTouchEvent(event);
	}

	private boolean proxyMotionEvent(MotionEvent event, MotionEventProxyMethod method) {
	float dx = mCurrentRecyclerView.getLeft() - getLeft();
	float dy = mCurrentRecyclerView.getTop() - getTop();
	event.offsetLocation(dx, dy);
	try {
	return method.proxyEvent(mCurrentRecyclerView, event);
	} finally {
	event.offsetLocation(-dx, -dy);
	}
	}

	@Override
	public void onChildViewAttachedToWindow(@NonNull View view) {
	if (view instanceof EmptySpaceView) {
	findCurrentEmptyView();
	}
	}

	@Override
	public void onChildViewDetachedFromWindow(@NonNull View view) {
	if (view == mCurrentEmptySpaceView) {
	findCurrentEmptyView();
	}
	}

	private void findCurrentEmptyView() {
	if (mCurrentEmptySpaceView != null) {
	mCurrentEmptySpaceView.setOnYChangeCallback(null);
	mCurrentEmptySpaceView = null;
	}
	int childCount = mCurrentRecyclerView.getChildCount();
	for (int i = 0; i < childCount; i++) {
	View view = mCurrentRecyclerView.getChildAt(i);
	if (view instanceof EmptySpaceView) {
	mCurrentEmptySpaceView = (EmptySpaceView) view;
	mCurrentEmptySpaceView.setFixedHeight(getHeaderHeight());
	mCurrentEmptySpaceView.setOnYChangeCallback(this::updateHeaderScroll);
	return;
	}
	}
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
	super.onLayout(changed, l, t, r, b);

	// Update various stick parameters
	int count = getChildCount();
	int stickyHeaderHeight = 0;
	for (int i = 0; i < count; i++) {
	View v = getChildAt(i);
	MyLayoutParams lp = (MyLayoutParams) v.getLayoutParams();
	if (lp.sticky) {
	lp.scrollLimit = -v.getTop() + stickyHeaderHeight;
	stickyHeaderHeight += v.getHeight();
	} else {
	lp.scrollLimit = Integer.MIN_VALUE;
	}
	}
	updateHeaderScroll();
	}

	@Override
	protected LayoutParams generateDefaultLayoutParams() {
	return new MyLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
	}

	@Override
	protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp) {
	return new MyLayoutParams(lp.width, lp.height);
	}

	@Override
	public LayoutParams generateLayoutParams(AttributeSet attrs) {
	return new MyLayoutParams(getContext(), attrs);
	}

	@Override
	protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
	return p instanceof MyLayoutParams;
	}

	private static class MyLayoutParams extends LayoutParams {

	public final boolean sticky;
	public int scrollLimit;

	MyLayoutParams(int width, int height) {
	super(width, height);
	sticky = false;
	}

	MyLayoutParams(Context c, AttributeSet attrs) {
	super(c, attrs);
	TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.StickyScroller_Layout);
	sticky = a.getBoolean(R.styleable.StickyScroller_Layout_layout_sticky, false);
	a.recycle();
	}
	}

	private interface MotionEventProxyMethod {

	boolean proxyEvent(ViewGroup view, MotionEvent event);
	}

	/**
	* Empty view which allows listening for 'Y' changes
	*/
	public static class EmptySpaceView extends View {

	private Runnable mOnYChangeCallback;
	private int mHeight = 0;

	public EmptySpaceView(Context context) {
	super(context);
	animate().setUpdateListener(v -> notifyYChanged());
	}

	/**
	* Sets the height for the empty view
	* @return true if the height changed, false otherwise
	*/
	public boolean setFixedHeight(int height) {
	if (mHeight != height) {
	mHeight = height;
	requestLayout();
	return true;
	}
	return false;
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	super.onMeasure(widthMeasureSpec, makeMeasureSpec(mHeight, EXACTLY));
	}

	public void setOnYChangeCallback(Runnable callback) {
	mOnYChangeCallback = callback;
	}

	@Override
	protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
	super.onLayout(changed, left, top, right, bottom);
	notifyYChanged();
	}

	@Override
	public void offsetTopAndBottom(int offset) {
	super.offsetTopAndBottom(offset);
	notifyYChanged();
	}

	@Override
	public void setTranslationY(float translationY) {
	super.setTranslationY(translationY);
	notifyYChanged();
	}

	private void notifyYChanged() {
	if (mOnYChangeCallback != null) {
	mOnYChangeCallback.run();
	}
	}
	}
	}