src/com/android/launcher3/BaseRecyclerView.java

/*
 * Copyright (C) 2015 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;

import android.content.Context;
import android.graphics.Canvas;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ViewGroup;
import android.widget.TextView;

import com.android.launcher3.views.RecyclerViewFastScroller;


/**
 * A base {@link RecyclerView}, which does the following:
 * <ul>
 *   <li> NOT intercept a touch unless the scrolling velocity is below a predefined threshold.
 *   <li> Enable fast scroller.
 * </ul>
 */
public abstract class BaseRecyclerView extends RecyclerView
        implements RecyclerView.OnItemTouchListener {

    protected RecyclerViewFastScroller mScrollbar;

    public BaseRecyclerView(Context context) {
        this(context, null);
    }

    public BaseRecyclerView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

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

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        addOnItemTouchListener(this);
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        ViewGroup parent = (ViewGroup) getParent();
        mScrollbar = parent.findViewById(R.id.fast_scroller);
        mScrollbar.setRecyclerView(this, (TextView) parent.findViewById(R.id.fast_scroller_popup));
    }

    /**
     * We intercept the touch handling only to support fast scrolling when initiated from the
     * scroll bar.  Otherwise, we fall back to the default RecyclerView touch handling.
     */
    @Override
    public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent ev) {
        return handleTouchEvent(ev);
    }

    @Override
    public void onTouchEvent(RecyclerView rv, MotionEvent ev) {
        handleTouchEvent(ev);
    }

    /**
     * Handles the touch event and determines whether to show the fast scroller (or updates it if
     * it is already showing).
     */
    private boolean handleTouchEvent(MotionEvent ev) {
        // Move to mScrollbar's coordinate system.
        int left = getLeft() - mScrollbar.getLeft();
        int top = getTop() - mScrollbar.getTop();
        ev.offsetLocation(left, top);
        try {
            return mScrollbar.handleTouchEvent(ev);
        } finally {
            ev.offsetLocation(-left, -top);
        }
    }

    public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        // DO NOT REMOVE, NEEDED IMPLEMENTATION FOR M BUILDS
    }

    /**
     * Returns the height of the fast scroll bar
     */
    public int getScrollbarTrackHeight() {
        return getHeight() - getPaddingTop() - getPaddingBottom();
    }

    /**
     * Returns the available scroll height:
     *   AvailableScrollHeight = Total height of the all items - last page height
     */
    protected abstract int getAvailableScrollHeight();

    /**
     * Returns the available scroll bar height:
     *   AvailableScrollBarHeight = Total height of the visible view - thumb height
     */
    protected int getAvailableScrollBarHeight() {
        int availableScrollBarHeight = getScrollbarTrackHeight() - mScrollbar.getThumbHeight();
        return availableScrollBarHeight;
    }

    /**
     * Returns the scrollbar for this recycler view.
     */
    public RecyclerViewFastScroller getScrollBar() {
        return mScrollbar;
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        onUpdateScrollbar(0);
        super.dispatchDraw(canvas);
    }

    /**
     * Updates the scrollbar thumb offset to match the visible scroll of the recycler view.  It does
     * this by mapping the available scroll area of the recycler view to the available space for the
     * scroll bar.
     *
     * @param scrollY the current scroll y
     */
    protected void synchronizeScrollBarThumbOffsetToViewScroll(int scrollY,
            int availableScrollHeight) {
        // Only show the scrollbar if there is height to be scrolled
        if (availableScrollHeight <= 0) {
            mScrollbar.setThumbOffsetY(-1);
            return;
        }

        // Calculate the current scroll position, the scrollY of the recycler view accounts for the
        // view padding, while the scrollBarY is drawn right up to the background padding (ignoring
        // padding)
        int scrollBarY =
                (int) (((float) scrollY / availableScrollHeight) * getAvailableScrollBarHeight());

        // Calculate the position and size of the scroll bar
        mScrollbar.setThumbOffsetY(scrollBarY);
    }

    /**
     * @return whether fast scrolling is supported in the current state.
     */
    public boolean supportsFastScrolling() {
        return true;
    }

    /**
     * Maps the touch (from 0..1) to the adapter position that should be visible.
     * <p>Override in each subclass of this base class.
     *
     * @return the scroll top of this recycler view.
     */
    public abstract int getCurrentScrollY();

    /**
     * Maps the touch (from 0..1) to the adapter position that should be visible.
     * <p>Override in each subclass of this base class.
     */
    public abstract String scrollToPositionAtProgress(float touchFraction);

    /**
     * Updates the bounds for the scrollbar.
     * <p>Override in each subclass of this base class.
     */
    public abstract void onUpdateScrollbar(int dy);

    /**
     * <p>Override in each subclass of this base class.
     */
    public void onFastScrollCompleted() {}
}