/*
* 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 com.android.launcher3.util.Thunk;
/**
* 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 {
private static final int SCROLL_DELTA_THRESHOLD_DP = 4;
/** Keeps the last known scrolling delta/velocity along y-axis. */
@Thunk int mDy = 0;
private float mDeltaThreshold;
protected final BaseRecyclerViewFastScrollBar mScrollbar;
private int mDownX;
private int mDownY;
private int mLastY;
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);
mDeltaThreshold = getResources().getDisplayMetrics().density * SCROLL_DELTA_THRESHOLD_DP;
mScrollbar = new BaseRecyclerViewFastScrollBar(this, getResources());
ScrollListener listener = new ScrollListener();
setOnScrollListener(listener);
}
private class ScrollListener extends OnScrollListener {
public ScrollListener() {
// Do nothing
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
mDy = dy;
// TODO(winsonc): If we want to animate the section heads while scrolling, we can
// initiate that here if the recycler view scroll state is not
// RecyclerView.SCROLL_STATE_IDLE.
onUpdateScrollbar(dy);
}
}
public void reset() {
mScrollbar.reattachThumbToScroll();
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
addOnItemTouchListener(this);
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
mScrollbar.setPopupView(((ViewGroup) getParent()).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) {
int action = ev.getAction();
int x = (int) ev.getX();
int y = (int) ev.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
// Keep track of the down positions
mDownX = x;
mDownY = mLastY = y;
if (shouldStopScroll(ev)) {
stopScroll();
}
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
case MotionEvent.ACTION_MOVE:
mLastY = y;
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
onFastScrollCompleted();
mScrollbar.handleTouchEvent(ev, mDownX, mDownY, mLastY);
break;
}
return mScrollbar.isDraggingThumb();
}
public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
// DO NOT REMOVE, NEEDED IMPLEMENTATION FOR M BUILDS
}
/**
* Returns whether this {@link MotionEvent} should trigger the scroll to be stopped.
*/
protected boolean shouldStopScroll(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
if ((Math.abs(mDy) < mDeltaThreshold &&
getScrollState() != RecyclerView.SCROLL_STATE_IDLE)) {
// now the touch events are being passed to the {@link WidgetCell} until the
// touch sequence goes over the touch slop.
return true;
}
}
return false;
}
/**
* Returns the height of the fast scroll bar
*/
protected int getScrollbarTrackHeight() {
return getHeight();
}
/**
* 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 track color (ignoring alpha), can be overridden by each subclass.
*/
public int getFastScrollerTrackColor(int defaultTrackColor) {
return defaultTrackColor;
}
/**
* Returns the scrollbar for this recycler view.
*/
public BaseRecyclerViewFastScrollBar getScrollBar() {
return mScrollbar;
}
@Override
protected void dispatchDraw(Canvas canvas) {
super.dispatchDraw(canvas);
onUpdateScrollbar(0);
mScrollbar.draw(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.
*/
protected 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.
*/
protected abstract String scrollToPositionAtProgress(float touchFraction);
/**
* Updates the bounds for the scrollbar.
* <p>Override in each subclass of this base class.
*/
protected abstract void onUpdateScrollbar(int dy);
/**
* <p>Override in each subclass of this base class.
*/
protected void onFastScrollCompleted() {}
}