以编程方式结束 Android DragEvent

Question

我正在使用 3.0 中引入的拖放 API - 但是，我只希望当用户手指位于屏幕的某一特定区域内时，拖动阴影能够跟随用户的手指。如果他们漂到外面，我希望阴影消失并且拖动事件结束。我已经做了一些搜索，发现 API 不支持在创建后更新拖动阴影，这是我的第一个计划，但是有没有办法在用户不实际抬起手指的情况下停止 DragEvent？

Answer 1

这个问题很老了，但因为没有答案；我想提醒大家注意，根据官方文档和 API，这现在是默认行为此处的官方文档和 API，这现在是默认行为

可以使用以下引用的代码来实现此行为：

val imageView = ImageView(this)

// Set the drag event listener for the View.
imageView.setOnDragListener { v, e ->

    // Handles each of the expected events.
    when (e.action) {
        DragEvent.ACTION_DRAG_STARTED -> {
            // Determines if this View can accept the dragged data.
            if (e.clipDescription.hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) {
                // As an example of what your application might do, applies a blue color tint
                // to the View to indicate that it can accept data.
                (v as? ImageView)?.setColorFilter(Color.BLUE)

                // Invalidate the view to force a redraw in the new tint.
                v.invalidate()

                // Returns true to indicate that the View can accept the dragged data.
                true
            } else {
                // Returns false to indicate that, during the current drag and drop operation,
                // this View will not receive events again until ACTION_DRAG_ENDED is sent.
                false
            }
        }
        DragEvent.ACTION_DRAG_ENTERED -> {
            // Applies a green tint to the View.
            (v as? ImageView)?.setColorFilter(Color.GREEN)

            // Invalidates the view to force a redraw in the new tint.
            v.invalidate()

            // Returns true; the value is ignored.
            true
        }

        DragEvent.ACTION_DRAG_LOCATION ->
            // Ignore the event.
            true
        DragEvent.ACTION_DRAG_EXITED -> {
            // Resets the color tint to blue.
            (v as? ImageView)?.setColorFilter(Color.BLUE)

            // Invalidates the view to force a redraw in the new tint.
            v.invalidate()

            // Returns true; the value is ignored.
            true
        }
        DragEvent.ACTION_DROP -> {
            // Gets the item containing the dragged data.
            val item: ClipData.Item = e.clipData.getItemAt(0)

            // Gets the text data from the item.
            val dragData = item.text

            // Displays a message containing the dragged data.
            Toast.makeText(this, "Dragged data is $dragData", Toast.LENGTH_LONG).show()

            // Turns off any color tints.
            (v as? ImageView)?.clearColorFilter()

            // Invalidates the view to force a redraw.
            v.invalidate()

            // Returns true. DragEvent.getResult() will return true.
            true
        }

        DragEvent.ACTION_DRAG_ENDED -> {
            // Turns off any color tinting.
            (v as? ImageView)?.clearColorFilter()

            // Invalidates the view to force a redraw.
            v.invalidate()

            // Does a getResult(), and displays what happened.
            when(e.result) {
                true ->
                    Toast.makeText(this, "The drop was handled.", Toast.LENGTH_LONG)
                else ->
                    Toast.makeText(this, "The drop didn't work.", Toast.LENGTH_LONG)
            }.show()

            // Returns true; the value is ignored.
            true
        }
        else -> {
            // An unknown action type was received.
            Log.e("DragDrop Example", "Unknown action type received by View.OnDragListener.")
            false
        }
    }
}