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A simple RecyclerView scrolling tricks.
/*
* The MIT License (MIT)
*
* Copyright (c) 2015 longkai
*
* The software shall be used for good, not evil.
*/
package android.support.animation;
import android.content.Context;
import android.support.annotation.IntDef;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.ViewConfiguration;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
/**
* A simple {@code RecyclerView} scrolling tricks.
* <p>
* NOTE: the gathered scrollY may not the same as the user scroll distance.
*
* @author longkai
*/
public abstract class QuickReturnRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
public static final int LINEAR = 0;
public static final int GRID = 1;
public static final int STAGGERED_GRID = 2;
// more customized layout manager goes here
private static final int TOUCH_SLOP_FACTOR = 3;
@Retention(RetentionPolicy.SOURCE)
@IntDef({LINEAR, GRID, STAGGERED_GRID})
public @interface LayoutManager {
}
@LayoutManager private final int mLayoutManager;
private final int mTouchSlop;
private final int mTopOffset;
private int mScrollY;
private boolean mVisible = true;
private int[] mPositions; // currently only for the staggered grid layout manager
public QuickReturnRecyclerOnScrollListener(Context context, int offset, @LayoutManager int layoutManager) {
mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop() * TOUCH_SLOP_FACTOR;
mTopOffset = offset;
mLayoutManager = layoutManager;
}
public QuickReturnRecyclerOnScrollListener(Context context, @LayoutManager int layoutManager) {
this(context, -1, layoutManager);
}
public QuickReturnRecyclerOnScrollListener(Context context) {
this(context, -1, LINEAR);
}
/**
* Notify that the caller needs to handle hide animation.
*
* @param dy currently scrollY since last animation if any
*/
protected abstract void onHide(int dy);
/**
* Notify that the caller needs to handle show animation.
*
* @param dy currently scrollY since last animation if any
*/
protected abstract void onShow(int dy);
@Override public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
// if the user stop scroll, reset the current scrollY
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
mScrollY = 0;
}
}
@Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int firstPosition = findFirstPosition(recyclerView);
if (mTopOffset > 0 && firstPosition < mTopOffset) {
handleOffsetScrolling(recyclerView);
} else {
// handle scroll
quickReturn();
}
// finally, gather dy
if ((mVisible && dy > 0) || (!mVisible && dy < 0)) {
mScrollY += dy;
}
}
private void quickReturn() {
if (mScrollY > mTouchSlop && mVisible) {
// up
onHide(mScrollY);
mVisible = false;
mScrollY = 0;
} else if (mScrollY < -mTouchSlop && !mVisible) {
// down
onShow(mScrollY);
mVisible = true;
mScrollY = 0;
}
}
private void handleOffsetScrolling(RecyclerView recyclerView) {
if (!mVisible) {
onShow(mScrollY);
mVisible = true;
mScrollY = 0;
}
}
private int findFirstPosition(RecyclerView recyclerView) {
int firstPosition = -1;
switch (mLayoutManager) {
case LINEAR:
firstPosition = ((LinearLayoutManager) recyclerView.getLayoutManager()).findFirstVisibleItemPosition();
break;
case GRID:
firstPosition = ((GridLayoutManager) recyclerView.getLayoutManager()).findFirstVisibleItemPosition();
break;
case STAGGERED_GRID:
StaggeredGridLayoutManager lm = (StaggeredGridLayoutManager) recyclerView.getLayoutManager();
if (mPositions == null) {
mPositions = new int[lm.getSpanCount()];
}
lm.findFirstVisibleItemPositions(mPositions);
final int count = mPositions.length;
for (int i = 0; i < count; i++) {
firstPosition = Math.min(firstPosition, mPositions[i]);
}
break;
}
return firstPosition;
}
public static @QuickReturnRecyclerOnScrollListener.LayoutManager int resolveLayoutManager(RecyclerView recyclerView) {
RecyclerView.LayoutManager lm = recyclerView.getLayoutManager();
if (lm instanceof LinearLayoutManager) {
return LINEAR;
} else if (lm instanceof GridLayoutManager) {
return GRID;
} else if (lm instanceof StaggeredGridLayoutManager) {
return STAGGERED_GRID;
}
// default
return LINEAR;
}
}
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