列表视图项滚动动画（“UIKit Dynamics” -like）

Question

当发生滚动时，我试图将< code>ListView项目动画化。更具体地说，我正试图模仿iOS 7上iMessage应用程序的滚动动画。我在网上找到一个类似的例子:

为了澄清，我试图在用户滚动时实现对项目的“流体”移动效果，而不是在添加新项目时实现动画。我试图修改我的BaseAdapter中的视图，并且我已经研究了AbsListView源代码，看看我是否可以以某种方式在某个地方附加一个加速插值器，该器可以调整发送到子视图的绘制坐标（如果这是AbsListView的设计方式）。到目前为止，我一直无法取得任何进展。

有没有人对如何复制这种行为有任何想法？

为了记录在案，以帮助谷歌搜索：这在ios上被称为“UIKit Dynamics”。

如何在iOS 7中复制弹出气泡的消息

它内置于最近的iOS版本中。但是，它仍然有点难以使用。（2014）这是每个人都复制的帖子：广泛复制的文章 令人惊讶的是，UIKit Dynamics仅在Apple的“集合视图”上可用，而不是在Apple的“表视图”上可用，因此所有iOS debs都必须将内容从表视图转换为“集合视图”。

每个人都使用作为起点的库是BPXLFlowLayout，因为那个人几乎破解了iPhone短信应用程序的感觉。事实上，如果你把它移植到Android上，我想你可以使用那里的参数来获得相同的感觉。仅供参考，我注意到在我的Android fone系列中，HTC手机在其UI上具有这种效果。希望它有帮助。Android摇滚！

Answer 1

在返回convertView之前，将其放入getView（）方法中：

Animation animationY = new TranslateAnimation(0, 0, holder.llParent.getHeight()/4, 0);
animationY.setDuration(1000);
Yourconvertview.startAnimation(animationY);  
animationY = null; 

其中 llParent = RootLayout，它由自定义行项组成。

Answer 2

我只花了几分钟来探索这个问题，看起来使用API 12及更高版本可以很容易地完成它（希望我没有错过什么...）。要获得非常基本的卡片效果，只需在您的适配器中getView（）的末尾执行几行代码，然后再将其返回列表。这是整个适配器：

    public class MyAdapter extends ArrayAdapter<String>{

        private int mLastPosition;

        public MyAdapter(Context context, ArrayList<String> objects) {
            super(context, 0, objects);
        }

        private class ViewHolder{
            public TextView mTextView;
        }

        @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            ViewHolder holder;

            if (convertView == null) {
                holder = new ViewHolder();
                convertView = LayoutInflater.from(getContext()).inflate(R.layout.grid_item, parent, false);
                holder.mTextView = (TextView) convertView.findViewById(R.id.checkbox);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }

            holder.mTextView.setText(getItem(position));

            // This tells the view where to start based on the direction of the scroll.
            // If the last position to be loaded is <= the current position, we want
            // the views to start below their ending point (500f further down).
            // Otherwise, we start above the ending point.
            float initialTranslation = (mLastPosition <= position ? 500f : -500f);

            convertView.setTranslationY(initialTranslation);
            convertView.animate()
                    .setInterpolator(new DecelerateInterpolator(1.0f))
                    .translationY(0f)
                    .setDuration(300l)
                    .setListener(null);

            // Keep track of the last position we loaded
            mLastPosition = position;

            return convertView;
        }


    }

请注意，我记录了最后一个要加载的位置(mLastPosition ),以便确定是从底部向上(如果向下滚动)还是从顶部向下(如果向上滚动)激活视图。

奇妙的是，只需修改初始的convertView属性（例如convertView.setScaleX（浮点缩放））和convertViews，您就可以做更多的事情。动画（）链（例如，scaleX（float））。

Answer 3

这个实现非常有效。不过也有一些闪烁，可能是因为适配器在顶部或底部添加新视图时改变了索引。这可以通过观察树中的变化并动态移动索引来解决。。

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));

        //check for bounds
        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;

}

}