ItemTouchHelper:防止越界拖动 [英] ItemTouchHelper: Prevent out of bounds dragging

问题描述

我有一个使用ItemTouchHelper的回收站视图.它允许拖动项目.

I have a recycler view with ItemTouchHelper. It allows dragging the items.

我想将拖动限制在回收站视图的范围内-即，您不能只是将视图拖动到容器外，以使其消失.

I want to limit the dragging to the bounds of recycler view - i.e. you can't just drag the view outside the container, so that it disappears.

我试图像这样检查绝对坐标:

I tried checking the absolute coordinates like this:

 @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);
...
}

但是后来我遇到了某种程度的渲染一致性-如果我缓慢移动视图，则超出范围时它将停止移动，但是如果我移动得更快，则无论如何它都会离开回收者视图的范围.

but then I run into kinda rendering concurency - if I move the view slowly, it will stop moving when going out of bounds, but if I move faster - then it anyway leaves the recycler view bounds.

有什么想法/方法吗?

推荐答案

dY和dX值必须裁剪为 RecyclerView 的范围:

The dY and dX value must be clipped to the RecyclerView's bounds:

override fun onChildDraw(c: Canvas, recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) {
    val clippedDx  = clip(recyclerView.width, viewHolder.itemView.left, viewHolder.itemView.right, dX)
    val clippedDy  = clip(recyclerView.height, viewHolder.itemView.top, viewHolder.itemView.bottom, dY)
    super.onChildDraw(c, recyclerView, viewHolder, clippedDx, clippedDy, actionState, isCurrentlyActive)
}

private fun clip(size: Int, start: Int, end: Int, delta: Float): Float {
    val newStart = start + delta
    val newEnd = end + delta

    val oobStart = 0 - newStart
    val oobEnd = newEnd - size

    return when {
        oobStart > 0 -> delta + oobStart
        oobEnd > 0 -> delta - oobEnd
        else -> delta
    }
}

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