stackoverflow上看到这个问题，答主给了个demo
http://stackoverflow.com/questions/27446051/recyclerview-animate-item-resize
看懂了之后发个博，记录一下，刚开始看别人代码好难受，就这么3个文件看了一晚上。。
效果如下
res文件
main_activity文件就是一个recyclerview
main_item是两个textview 一个标题一个详细信息
MainActivity就是加载了一个RecyclerView
public class MainActivity extends ActionBarActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main_activity); final RecyclerView rv = (RecyclerView) findViewById(R.id.rv); final LinearLayoutManager layoutManager = new LinearLayoutManager(this); rv.setLayoutManager(layoutManager); final MainAdapter adapter = new MainAdapter(); rv.setAdapter(adapter); } }- 1
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MainAdapter中new了一个keepOne对象，点进去看这个类，有两个方法：bind和toggle，其中的bind是在MainAdapter中的onBindViewHolder（）方法中调用，而toggle是响应viewholder的点击事件
public static class KeepOneH<VH extends RecyclerView.ViewHolder & Expandable> { // opened为-1表示所有item是关闭状态，open为pos值的表示pos位置的item为展开的状态 private int _opened = -1; public void bind(VH holder, int pos) { if (pos == _opened) // 3 // 直接显示expandView 无动画 ExpandableViewHoldersUtil.openH(holder, holder.getExpandView(), false); else // 直接关闭expandView 无动画 ExpandableViewHoldersUtil.closeH(holder, holder.getExpandView(), false); } - 1
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@SuppressWarnings("unchecked")
// 响应点击事件的方法
public void toggle(VH holder) { // 如果点击的就是开着的item，就关闭该item并把opened置-1 // ???TODO if (_opened == holder.getPosition()) { _opened = -1; // 关闭expandView 有动画 ExpandableViewHoldersUtil.closeH(holder, holder.getExpandView(), true); } // 如果点击其他本来关闭着的item，则把opened值换成当前pos，把之前开的item给关掉 else { int previous = _opened; _opened = holder.getPosition(); // 展开expandView 有动画 ExpandableViewHoldersUtil.openH(holder, holder.getExpandView(), true); // 用动画关闭之前的item final VH oldHolder = (VH) ((RecyclerView) holder.itemView.getParent()).findViewHolderForPosition(previous); if (oldHolder != null) ExpandableViewHoldersUtil.closeH(oldHolder, oldHolder.getExpandView(), true); } } }- 1
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点进openH和closeH方法进去看
// 4
public static void openH(final RecyclerView.ViewHolder holder, final View expandView, final boolean animate) { // animate参数为true，则有动画效果 if (animate) { expandView.setVisibility(View.VISIBLE); // 5 // 改变高度的动画，具体操作点进去看 final Animator animator = ViewHolderAnimator.ofItemViewHeight(holder); // 扩展的动画结束后透明度动画开始 animator.addListener(new AnimatorListenerAdapter() { @Override public void onAnimationEnd(Animator animation) { final ObjectAnimator alphaAnimator = ObjectAnimator.ofFloat(expandView, View.ALPHA, 1); alphaAnimator.addListener(new ViewHolderAnimator.ViewHolderAnimatorListener(holder)); alphaAnimator.start(); } }); animator.start(); } // animate参数为false，则直接设置为可见 else { expandView.setVisibility(View.VISIBLE); expandView.setAlpha(1); } }- 1
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openH方法接收3个参数，
第一个是viewholder.
第二个是展开部分的view，由holder.getExpandView()方法获取。这里定义了一个接口
public static interface Expandable {
public View getExpandView(); }- 1
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在MainAdapter中传入infos这个Textview
@Override
public View getExpandView() {
return infos;
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第三个是一个标记，true时有动画，false时直接设置其展开或者是关闭的状态。所以在bind()方法中调用的openH()都是false，而toggle()中调用的设置为true。
openH方法中 具体动画的操作为ViewHolderAnimator.ofItemViewHeight(holder)
public static Animator ofItemViewHeight(RecyclerView.ViewHolder holder) {
View parent = (View) holder.itemView.getParent();
if (parent == null)
throw new IllegalStateException("Cannot animate the layout of a view that has no parent"); // 测量扩展动画的起始高度和结束高度 int start = holder.itemView.getMeasuredHeight(); holder.itemView.measure(View.MeasureSpec.makeMeasureSpec(parent.getMeasuredWidth(), View.MeasureSpec.AT_MOST), View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED)); int end = holder.itemView.getMeasuredHeight(); // 6 final Animator animator = LayoutAnimator.ofHeight(holder.itemView, start, end); // 设定该item在动画开始结束和取消时能否被recycle animator.addListener(new ViewHolderAnimatorListener(holder)); // 设定结束时这个item的宽高 animator.addListener(new LayoutParamsAnimatorListener(holder.itemView, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT)); return animator; }- 1
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可以看出 具体展开的动画在LayoutAnimator.ofHeight(holder.itemView, start, end);中，ViewHolderAnimator只是测量参数，设定监听两个监听事件
1设定在动画开始结束和取消状态下是否可以被回收
public ViewHolderAnimatorListener(RecyclerView.ViewHolder holder) {
_holder = holder;
}
@Override
public void onAnimationStart(Animator animation) { _holder.setIsRecyclable(false); } @Override public void onAnimationEnd(Animator animation) { _holder.setIsRecyclable(true); } @Override public void onAnimationCancel(Animator animation) { _holder.setIsRecyclable(true); } }- 1
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2.设定在动画结束后view的高和宽分别为warp_content,match_parent.
public static class LayoutParamsAnimatorListener extends AnimatorListenerAdapter { private final View _view; private final int _paramsWidth; private final int _paramsHeight; public LayoutParamsAnimatorListener(View view, int paramsWidth, int paramsHeight) { _view = view; _paramsWidth = paramsWidth; _paramsHeight = paramsHeight; } @Override public void onAnimationEnd(Animator animation) { final ViewGroup.LayoutParams params = _view.getLayoutParams(); params.width = _paramsWidth; params.height = _paramsHeight; _view.setLayoutParams(params); } }- 1
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再深入一层看展开的动画
public class LayoutAnimator {
public static class LayoutHeightUpdateListener implements ValueAnimator.AnimatorUpdateListener { private final View _view; public LayoutHeightUpdateListener(View view) { _view = view; } @Override public void onAnimationUpdate(ValueAnimator animation) { final ViewGroup.LayoutParams lp = _view.getLayoutParams(); lp.height = (int) animation.getAnimatedValue(); _view.setLayoutParams(lp); } } public static Animator ofHeight(View view, int start, int end) { final ValueAnimator animator = ValueAnimator.ofInt(start, end); animator.addUpdateListener(new LayoutHeightUpdateListener(view)); return animator; } }- 1
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是用ValueAnimator.ofInt生成一系列高度值，然后监听动画的变化，不断设定view的高度值
http://blog.csdn.net/gulumi_mmga/article/details/46683437
本文转自 一点点征服 博客园博客，原文链接：http://www.cnblogs.com/ldq2016/p/5825015.html，如需转载请自行联系原作者
