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;
}
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);
}
}
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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);
}
}
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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;
}
}
