这个实现相当不错。虽然会有一些闪烁,但可能是因为适配器将新视图添加到顶部或底部时索引被更改了..这可以通过观察树中的变化并在运行时移动索引来解决。
public class ElasticListView extends GridView implements AbsListView.OnScrollListener, View.OnTouchListener {
private static int SCROLLING_UP = 1;
private static int SCROLLING_DOWN = 2;
private int mScrollState;
private int mScrollDirection;
private int mTouchedIndex;
private View mTouchedView;
private int mScrollOffset;
private int mStartScrollOffset;
private boolean mAnimate;
private HashMap<View, ViewPropertyAnimator> animatedItems;
public ElasticListView(Context context) {
super(context);
init();
}
public ElasticListView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public ElasticListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mScrollState = SCROLL_STATE_IDLE;
mScrollDirection = 0;
mStartScrollOffset = -1;
mTouchedIndex = Integer.MAX_VALUE;
mAnimate = true;
animatedItems = new HashMap<>();
this.setOnTouchListener(this);
this.setOnScrollListener(this);
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (mScrollState != scrollState) {
mScrollState = scrollState;
mAnimate = true;
}
if (scrollState == SCROLL_STATE_IDLE) {
mStartScrollOffset = Integer.MAX_VALUE;
mAnimate = true;
startAnimations();
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (mScrollState == SCROLL_STATE_TOUCH_SCROLL) {
if (mStartScrollOffset == Integer.MAX_VALUE) {
mTouchedView = getChildAt(mTouchedIndex - getPositionForView(getChildAt(0)));
if (mTouchedView == null) return;
mStartScrollOffset = mTouchedView.getTop();
} else if (mTouchedView == null) return;
mScrollOffset = mTouchedView.getTop() - mStartScrollOffset;
int tmpScrollDirection;
if (mScrollOffset > 0) {
tmpScrollDirection = SCROLLING_UP;
} else {
tmpScrollDirection = SCROLLING_DOWN;
}
if (mScrollDirection != tmpScrollDirection) {
startAnimations();
mScrollDirection = tmpScrollDirection;
}
if (Math.abs(mScrollOffset) > 200) {
mAnimate = false;
startAnimations();
}
Log.d("test", "direction:" + (mScrollDirection == SCROLLING_UP ? "up" : "down") + ", scrollOffset:" + mScrollOffset + ", toucheId:" + mTouchedIndex + ", fvisible:" + firstVisibleItem + ", " +
"visibleItemCount:" + visibleItemCount + ", " +
"totalCount:" + totalItemCount);
int indexOfLastAnimatedItem = mScrollDirection == SCROLLING_DOWN ?
getPositionForView(getChildAt(0)) + getChildCount() :
getPositionForView(getChildAt(0));
if (indexOfLastAnimatedItem >= getChildCount()) {
indexOfLastAnimatedItem = getChildCount() - 1;
} else if (indexOfLastAnimatedItem < 0) {
indexOfLastAnimatedItem = 0;
}
if (mScrollDirection == SCROLLING_DOWN) {
setAnimationForScrollingDown(mTouchedIndex - getPositionForView(getChildAt(0)), indexOfLastAnimatedItem, firstVisibleItem);
} else {
setAnimationForScrollingUp(mTouchedIndex - getPositionForView(getChildAt(0)), indexOfLastAnimatedItem, firstVisibleItem);
}
if (Math.abs(mScrollOffset) > 200) {
mAnimate = false;
startAnimations();
mTouchedView = null;
mScrollDirection = 0;
mStartScrollOffset = -1;
mTouchedIndex = Integer.MAX_VALUE;
mAnimate = true;
}
}
}
private void startAnimations() {
for (ViewPropertyAnimator animator : animatedItems.values()) {
animator.start();
}
animatedItems.clear();
}
private void setAnimationForScrollingDown(int indexOfTouchedChild, int indexOflastAnimatedChild, int firstVisibleIndex) {
for (int i = indexOfTouchedChild + 1; i <= indexOflastAnimatedChild; i++) {
View v = getChildAt(i);
v.setTranslationY((-1f * mScrollOffset));
if (!animatedItems.containsKey(v)) {
animatedItems.put(v, v.animate().translationY(0).setDuration(300).setStartDelay(50 * i));
}
}
}
private void setAnimationForScrollingUp(int indexOfTouchedChild, int indexOflastAnimatedChild, int firstVisibleIndex) {
for (int i = indexOfTouchedChild - 1; i > 0; i--) {
View v = getChildAt(i);
v.setTranslationY((-1 * mScrollOffset));
if (!animatedItems.containsKey(v)) {
animatedItems.put(v, v.animate().translationY(0).setDuration(300).setStartDelay(50 * (indexOfTouchedChild - i)));
}
}
}
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
Rect rect = new Rect();
int childCount = getChildCount();
int[] listViewCoords = new int[2];
getLocationOnScreen(listViewCoords);
int x = (int)event.getRawX() - listViewCoords[0];
int y = (int)event.getRawY() - listViewCoords[1];
View child;
for (int i = 0; i < childCount; i++) {
child = getChildAt(i);
child.getHitRect(rect);
if (rect.contains(x, y)) {
mTouchedIndex = getPositionForView(child);
break;
}
}
return false;
}
return false;
}
}