RecyclerView ItemTouchHelper.Callback: 拖动交换条件

Question

我想实现拖动卡片的方式，即当我拖动的卡片没有完全与元素重叠，但只有 50% 时，卡片的重新排列开始。

查看示例：

现在，为了让右边的卡片向左移动，我需要将它与我正在拖动的卡片完全重叠。

我尝试从 ItemTouchHelper.Callback 覆盖此方法：

 public float getMoveThreshold(@NonNull ViewHolder viewHolder) {
     return .5f;
 }

但是没有用。

那么我怎样才能使交换发生在 50% 而不是 100% 的重叠？

Answer 1

我没有解决办法，但我还是想分享一下我的观察。似乎您从 getMoveThreshold() 方法 return 得到的任何值低于 1 都不会改变默认行为，但是，实际上高于 1 的值会改变。

Answer 2

经过多次尝试，自己找到了解决办法：

您需要覆盖 ItemTouchHelper.Callback 中的 chooseDropTarget 方法。

我是这样做的：

  //  x ≥ 0.5 (if less than 0.5, it will shake due to constant overlap)
val DRAG_THRESHOLD_PERSENT = 0.5
override fun chooseDropTarget(
    selected: ViewHolder,
    targets: MutableList<ViewHolder>,
    curX: Int, curY: Int
): ViewHolder? {
    val verticalOffset = (selected.itemView.height * DRAG_THRESHOLD_PERSENT).toInt()
    val horizontalOffset = (selected.itemView.width * DRAG_THRESHOLD_PERSENT).toInt()
    val left = curX - horizontalOffset
    val right = curX + selected.itemView.width + horizontalOffset
    val top = curY - verticalOffset
    val bottom = curY + selected.itemView.height + verticalOffset
    var winner: ViewHolder? = null
    var winnerScore = -1
    val dx = curX - selected.itemView.left
    val dy = curY - selected.itemView.top
    val targetsSize = targets.size
    for (i in 0 until targetsSize) {
        val target = targets[i]
        if (dx > 0) {
            val diff = target.itemView.right - right
            if (diff < 0 && target.itemView.right > selected.itemView.right) {
                val score = abs(diff)
                if (score > winnerScore) {
                    winnerScore = score
                    winner = target
                }
            }
        }
        if (dx < 0) {
            val diff = target.itemView.left - left
            if (diff > 0 && target.itemView.left < selected.itemView.left) {
                val score = abs(diff)
                if (score > winnerScore) {
                    winnerScore = score
                    winner = target
                }
            }
        }
        if (dy < 0) {
            val diff = target.itemView.top - top
            if (diff > 0 && target.itemView.top < selected.itemView.top) {
                val score = abs(diff)
                if (score > winnerScore) {
                    winnerScore = score
                    winner = target
                }
            }
        }
        if (dy > 0) {
            val diff = target.itemView.bottom - bottom
            if (diff < 0 && target.itemView.bottom > selected.itemView.bottom) {
                val score = abs(diff)
                if (score > winnerScore) {
                    winnerScore = score
                    winner = target
                }
            }
        }
    }
    return winner
}

工作原理：
我正在使用因子和 width/height 计算所选视图的偏移量。之后，我创建新的边框（左、右、上、下），向所选视图的边框添加偏移量，然后在方法

中使用它们代替原始边框

重要提示：

你不应该调用 super
系数必须大于0.5

RecyclerView ItemTouchHelper.Callback: 拖动交换条件

RecyclerView ItemTouchHelper.Callback: Dragging swap condition

java

android

drag-and-drop

android-recyclerview

itemtouchhelper