Question

我有一个带有ItemTouchHelper的回收者视图。它允许拖动项目。

我想将拖动限制在回收者视图的范围内 - 即您只能将视图拖到容器外部，以便它消失。

我试着像这样检查绝对坐标：

 @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        recyclerView.getLocationOnScreen(pos);
        int rvY = pos[1];
        viewHolder.itemView.getLocationOnScreen(pos);
        int vhY = pos[1];


        if (rvY > vhY || rvY + recyclerView.getHeight() < vhY + viewHolder.itemView.getHeight()) {
            return;
        }
super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
...
}

然后我遇到了有点渲染的可靠性 - 如果我慢慢地移动视图，它会在越界时停止移动，但如果我移动速度更快 - 那么无论如何它都会离开循环器视图边界。

任何想法/方法？

Answer 1

必须将dY值剪裁到回收器视图边界：

@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)
{
    float topY = viewHolder.itemView.getTop() + dY;
    float bottomY = topY + viewHolder.itemView.getHeight();
    if (topY < 0)
    {
        dY = 0;
    }
    else if (bottomY > recyclerView.getHeight())
    {
        dY = recyclerView.getHeight() - viewHolder.itemView.getHeight() - viewHolder.itemView.getTop();
    }
    super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

Answer 2

我调整了user1185087的答案，这样，如果拖动确实消失了，它就不会搬运您的物品，而只会搬运它。

@Override
public void onChildDraw(@NotNull Canvas c, @NotNull RecyclerView recyclerView,
                        @NotNull RecyclerView.ViewHolder viewHolder, float dX, float dY,
                        int actionState, boolean isCurrentlyActive) {
    float topY = viewHolder.itemView.getTop() + dY;
    float bottomY = topY + viewHolder.itemView.getHeight();

    // Only redraw child if it is inbounds of view
    if (topY > 0 && bottomY < recyclerView.getHeight()){
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }
}

Answer 3

我有同样的问题。所有的答案都帮助我找到了没有滞后的更好方法。：）

如果仅使用 dY ，则会产生滞后。因此，我在 onChildDraw 中为itemView添加位置确定。

override fun onChildDraw(c: Canvas, recyclerView: RecyclerView,
                         viewHolder: RecyclerView.ViewHolder, dX: Float, dY: Float,
                         actionState: Int, isCurrentlyActive: Boolean) {
    var edgeY = dY

    if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
        val lastPosition = (recyclerView.adapter?.itemCount ?: 0) - 1

        val view = viewHolder.itemView
        val pieceHeight = view.height / PIECE_RATIO

        val topEdge = recyclerView.top - pieceHeight
        val bottomEdge = recyclerView.height - view.bottom + pieceHeight

        if (movePosition == 0 && dY < topEdge) {
            edgeY = topEdge
        } else if (movePosition == lastPosition && dY > bottomEdge) {
            edgeY = bottomEdge
        }
    }

    super.onChildDraw(c, recyclerView, viewHolder, dX, edgeY, actionState, isCurrentlyActive)
}

PIECE_RATIO-查看可以走多远。
movePosition-拖动 viewHolder 的当前位置。需要最佳性能。您需要在 onSelectedChanged 和 onMove 中进行设置。在 clearView 中清除变量。

此代码：

/**
 * Variable need for best performance and more productive, because
 * get [RecyclerView.ViewHolder.getAdapterPosition] inside [onChildDraw]
 * is hard calculating operation
 */
protected var movePosition = RecyclerView.NO_POSITION

override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
    super.onSelectedChanged(viewHolder, actionState)

    /**
     * Get position on drag start
     */
    if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
        movePosition = viewHolder?.adapterPosition ?: RecyclerView.NO_POSITION
    }
}

override fun clearView(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder) {
    super.clearView(recyclerView, viewHolder)

    /**
     * Clear position on drag end
     */
    movePosition = RecyclerView.NO_POSITION
}

override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder,
                    target: RecyclerView.ViewHolder): Boolean {
    /**
     * Get position on drag
     */
    movePosition = target.adapterPosition
    return false
}

子类可以这样使用 movePosition ：

override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder,
                target: RecyclerView.ViewHolder): Boolean {
    super.onMove(recyclerView, viewHolder, target)
    return callback.onTouchMove(viewHolder.adapterPosition, movePosition)
}

您可以在以下链接中找到所有源代码和示例：github project

ItemTouchHelper：防止越界拖动

3 个答案: