RecyclerView问答

我认为您的动画无法正常工作，因为您不能以LayoutParams这种方式进行动画处理，即使可以的话，它也很整洁。我尝试了您拥有的代码，而所有操作只是使我的视野跃升到了新的高度。我发现使它起作用的唯一方法是使用a ValueAnimator，如下面的示例所示。

在使用DefaultItemAnimator来通过更新其可见性显示/隐藏视图时，我注意到了一些缺点。尽管它确实为新视图腾出了空间，并根据可扩展视图的可见性来对其余项目进行上下动画处理，但我注意到它并未使可扩展视图的高度动起来。仅使用alpha值，它就淡入淡出了。

以下是一个自定义文件ItemAnimator，它具有基于隐藏/显示布局LinearLayout中的大小和alpha动画的自定义ViewHolder。它还允许重复使用它们，ViewHolder并在用户快速点击标题时尝试正确处理部分动画：

public static class MyAnimator extends DefaultItemAnimator {
    @Override
    public boolean canReuseUpdatedViewHolder(RecyclerView.ViewHolder viewHolder) {
        return true;
    }

    private HashMap<RecyclerView.ViewHolder, AnimatorState> animatorMap = new HashMap<>();

    @Override
    public boolean animateChange(@NonNull RecyclerView.ViewHolder oldHolder, @NonNull final RecyclerView.ViewHolder newHolder, @NonNull ItemHolderInfo preInfo, @NonNull ItemHolderInfo postInfo) {
        final ValueAnimator heightAnim;
        final ObjectAnimator alphaAnim;

        final CustomAdapter.ViewHolder vh = (CustomAdapter.ViewHolder) newHolder;
        final View expandableView = vh.getExpandableView();
        final int toHeight; // save height for later in case reversing animation

        if(vh.isExpanded()) {
            expandableView.setVisibility(View.VISIBLE);

            // measure expandable view to get correct height
            expandableView.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
            toHeight = expandableView.getMeasuredHeight();
            alphaAnim = ObjectAnimator.ofFloat(expandableView, "alpha", 1f);
        } else {
            toHeight = 0;
            alphaAnim = ObjectAnimator.ofFloat(expandableView, "alpha", 0f);
        }

        heightAnim = ValueAnimator.ofInt(expandableView.getHeight(), toHeight);
        heightAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                expandableView.getLayoutParams().height = (Integer) heightAnim.getAnimatedValue();
                expandableView.requestLayout();
            }
        });

        AnimatorSet animSet = new AnimatorSet()
                .setDuration(getChangeDuration());
        animSet.playTogether(heightAnim, alphaAnim);
        animSet.addListener(new Animator.AnimatorListener() {
            private boolean isCanceled;

            @Override
            public void onAnimationStart(Animator animation) { }

            @Override
            public void onAnimationEnd(Animator animation) {
                if(!vh.isExpanded() && !isCanceled) {
                    expandableView.setVisibility(View.GONE);
                }

                dispatchChangeFinished(vh, false);
                animatorMap.remove(newHolder);
            }

            @Override
            public void onAnimationCancel(Animator animation) {
                isCanceled = true;
            }

            @Override
            public void onAnimationRepeat(Animator animation) { }
        });

        AnimatorState animatorState = animatorMap.get(newHolder);
        if(animatorState != null) {
            animatorState.animSet.cancel();

            // animation already running. Set start current play time of
            // new animations to keep them smooth for reverse animation
            alphaAnim.setCurrentPlayTime(animatorState.alphaAnim.getCurrentPlayTime());
            heightAnim.setCurrentPlayTime(animatorState.heightAnim.getCurrentPlayTime());

            animatorMap.remove(newHolder);
        }

        animatorMap.put(newHolder, new AnimatorState(alphaAnim, heightAnim, animSet));

        dispatchChangeStarting(newHolder, false);
        animSet.start();

        return false;
    }

    public static class AnimatorState {
        final ValueAnimator alphaAnim, heightAnim;
        final AnimatorSet animSet;

        public AnimatorState(ValueAnimator alphaAnim, ValueAnimator heightAnim, AnimatorSet animSet) {
            this.alphaAnim = alphaAnim;
            this.heightAnim = heightAnim;
            this.animSet = animSet;
        }
    }
}

这是使用稍作修改的RecyclerView演示后的结果。

更新：

刚注意到您的用例在重读问题后实际上有些不同。您有一个文本视图，只想显示一行，然后再将其展开以显示所有行。幸运的是，这简化了自定义动画制作器：

public static class MyAnimator extends DefaultItemAnimator {
    @Override
    public boolean canReuseUpdatedViewHolder(RecyclerView.ViewHolder viewHolder) {
        return true;
    }

    private HashMap<RecyclerView.ViewHolder, ValueAnimator> animatorMap = new HashMap<>();

    @Override
    public boolean animateChange(@NonNull RecyclerView.ViewHolder oldHolder, @NonNull final RecyclerView.ViewHolder newHolder, @NonNull ItemHolderInfo preInfo, @NonNull ItemHolderInfo postInfo) {
        ValueAnimator prevAnim = animatorMap.get(newHolder);
        if(prevAnim != null) {
            prevAnim.reverse();
            return false;
        }

        final ValueAnimator heightAnim;
        final CustomAdapter.ViewHolder vh = (CustomAdapter.ViewHolder) newHolder;
        final TextView tv = vh.getExpandableTextView();

        if(vh.isExpanded()) {
            tv.measure(View.MeasureSpec.makeMeasureSpec(((View) tv.getParent()).getWidth(), View.MeasureSpec.AT_MOST), View.MeasureSpec.UNSPECIFIED);
            heightAnim = ValueAnimator.ofInt(tv.getHeight(), tv.getMeasuredHeight());
        } else {
            Paint.FontMetrics fm = tv.getPaint().getFontMetrics();
            heightAnim = ValueAnimator.ofInt(tv.getHeight(), (int)(Math.abs(fm.top) + Math.abs(fm.bottom)));
        }

        heightAnim.setDuration(getChangeDuration());
        heightAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                tv.getLayoutParams().height = (Integer) heightAnim.getAnimatedValue();
                tv.requestLayout();
            }
        });

        heightAnim.addListener(new Animator.AnimatorListener() {
            @Override
            public void onAnimationEnd(Animator animation) {
                dispatchChangeFinished(vh, false);
                animatorMap.remove(newHolder);
            }

            @Override
            public void onAnimationCancel(Animator animation) { }

            @Override
            public void onAnimationStart(Animator animation) { }

            @Override
            public void onAnimationRepeat(Animator animation) { }
        });

        animatorMap.put(newHolder, heightAnim);

        dispatchChangeStarting(newHolder, false);
        heightAnim.start();

        return false;
    }
}

和新的演示：