Android 在 Recyclerview 中使用 itemTouchHelper 在 cardview 上拖动 elevation translationz

Question

我在弄清楚如何在拖动时临时提升 cardView 时遇到问题。我将回收器视图与 cardViews 一起使用，这是我的 itemtouchhelper:

class ListTouchHelper extends ItemTouchHelper.Callback {

    private final ActionCompletionContract contract;

    public ListTouchHelper(ActionCompletionContract contract) {
        this.contract = contract;
    }
    @Override
    public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
        int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
        int swipeFlags = ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
        return makeMovementFlags(dragFlags, swipeFlags);
    }

    @Override
    public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
        contract.onViewMoved(viewHolder.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
        if (direction == ItemTouchHelper.LEFT) {
            contract.onViewSwipedLeft(viewHolder.getAdapterPosition());
        } else if (direction == ItemTouchHelper.RIGHT) {
            contract.onViewSwipedRight(viewHolder.getAdapterPosition());
        }
    }

    public interface ActionCompletionContract {
        void onViewMoved(int oldPosition, int newPosition);
        void onViewSwipedLeft(int position);
        void onViewSwipedRight(int position);
    }
}

我已经设法暂时提升它：

这导致：（阴影以某种方式被剪掉了？）

但是，一旦稍微移动视图，高度就会消失：

我的问题是：如何在拖动卡片时获取高度（包括阴影）？

提前致谢！

Answer 1

好的，我解决了，有点。我认为由于某些其他原因它默认情况下不起作用，但是我设法编写了一个解决方法。

private boolean first = true; //first draw of cardView?
private boolean last = false; //last draw of cardView?

@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
    //add elevation on first draw
    if (first) {
        ViewPropertyAnimator animator = viewHolder.itemView.animate();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { //consider SDK version
            viewHolder.itemView.setTranslationZ(7);
            animator.start();
        }
        first = false;
    }
    //remove translationZ in last edit
    if (last) {
        ViewPropertyAnimator animator = viewHolder.itemView.animate();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) { //consider SDK version
            viewHolder.itemView.setTranslationZ(0);
            animator.start();
        }
        //reset values
        last=false;
        first=true;
    }
    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

@Override
public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
    super.clearView(recyclerView, viewHolder);
    last = true; //only one more OnChildDrawWillBeCalled
}

以上代码已添加到您的 ItemTouchHelper.Callback 中，一切都应该有效。基本思路是手动控制translationz的绘制。为此，我弄清楚第一个 canvas 何时绘制，最后一个何时绘制，而 cancas 将显示阴影。

Maxbe 再补充一条评论：ViewPropertyAnimator 与 xml 布局文件的结合非常不直观且存在错误，因此如果可以避免，我建议您这样做，而是尝试以编程方式为视图更改设置动画并效果。

希望这对某人有所帮助。

Answer 2

@LivinTheNoobLife 在您的解决方案中使用了 ViewPropertyAnimator，但您没有为其设置任何转换，因此不会应用任何动画。

这是我的解决方案，具有正常工作的浮动动画：

class DragHelper extends ItemTouchHelper.Callback {    
private boolean cardPicked = true;
private boolean reset = false;

@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {

    // elevate only when picked for the first time
    if (cardPicked) { 
        ViewPropertyAnimator animator = viewHolder.itemView.animate();
        animator.translationZ(16);
        animator.setDuration(200);
        animator.setInterpolator(new AccelerateDecelerateInterpolator());
        animator.start();

        cardPicked = false;
    }

    // when your item is not floating anymore
    if (reset){
        ViewPropertyAnimator animator = viewHolder.itemView.animate();

        animator.translationZ(0);
        animator.setDuration(200);
        animator.setInterpolator(new AccelerateInterpolator());
        animator.start();

        cardPicked = true;
        reset = false;
    }
    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

// As the doc says
// Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.
@Override
public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
    super.clearView(recyclerView, viewHolder);

     // interaction is over, time to reset our elevation
     reset = true;
}
}

Android 在 Recyclerview 中使用 itemTouchHelper 在 cardview 上拖动 elevation translationz

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