多窗口模式下的拖放

运行 Android 7.0（API 级别 24）或更高版本的设备支持多窗口模式，使用户可以通过拖放将数据从一个应用移动到另一个应用。

源应用（操作开始的地方）提供数据。目标应用（操作结束的地方）接收数据。

当用户开始拖动内容时，源应用应设置DRAG_FLAG_GLOBAL 标志以指示用户可以将数据拖动到另一个应用。

由于数据跨应用边界移动，因此应用使用内容 URI 共享对数据的访问。这需要以下内容

源应用必须设置DRAG_FLAG_GLOBAL_URI_READ 和DRAG_FLAG_GLOBAL_URI_WRITE 标志中的一个或两个，具体取决于源应用想要授予目标应用的读或写访问权限。
目标应用必须在处理用户拖入应用的数据之前立即调用requestDragAndDropPermissions()。如果目标应用不再需要访问拖动的数据，那么该应用可以对从requestDragAndDropPermissions()返回的对象调用release()。否则，权限将在包含的活动被销毁时释放。如果您的实现涉及启动新的 Activity 来处理已删除的 URI，则需要授予新 Activity 相同的权限。您必须设置剪贴板数据和一个标志
Kotlin
```
intent.setClipData(clipData)
intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
```
Java
```
intent.setClipData(clipData);
intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
```

以下代码片段演示了如何在用户删除操作发生后立即释放对拖动数据的只读访问权限。有关更完整的示例，请参见 GitHub 上的拖放演示。

源活动

Kotlin

// Drag a file stored in an images/ directory in internal storage.
val internalImagesDir = File(context.filesDir, "images")
val imageFile = File(internalImagesDir, imageFilename)
val uri = FileProvider.getUriForFile(context, contentAuthority, imageFile)

val listener = OnDragStartListener@{ view: View, _: DragStartHelper ->
    val clipData = ClipData(ClipDescription("Image Description",
                                            arrayOf("image/*")),
                            ClipData.Item(uri))
    // Must include DRAG_FLAG_GLOBAL to permit dragging data between apps.
    // This example provides read-only access to the data.
    val flags = View.DRAG_FLAG_GLOBAL or View.DRAG_FLAG_GLOBAL_URI_READ
    return@OnDragStartListener view.startDragAndDrop(clipData,
                                                     View.DragShadowBuilder(view),
                                                     null,
                                                     flags)
}

// Container where the image originally appears in the source app.
val srcImageView = findViewById<ImageView>(R.id.imageView)

// Detect and start the drag event.
DragStartHelper(srcImageView, listener).apply {
    attach()
}

Java

// Drag a file stored in an images/ directory in internal storage.
File internalImagesDir = new File(context.getFilesDir(), "images");
File imageFile = new File(internalImagesDir, imageFilename);
final Uri uri = FileProvider.getUriForFile(context, contentAuthority, imageFile);

// Container where the image originally appears in the source app.
ImageView srcImageView = findViewById(R.id.imageView);

// Enable the view to detect and start the drag event.
new DragStartHelper(srcImageView, (view, helper) -> {
    ClipData clipData = new ClipData(new ClipDescription("Image Description",
                                                          new String[] {"image/*"}),
                                     new ClipData.Item(uri));
    // Must include DRAG_FLAG_GLOBAL to permit dragging data between apps.
    // This example provides read-only access to the data.
    int flags = View.DRAG_FLAG_GLOBAL | View.DRAG_FLAG_GLOBAL_URI_READ;
    return view.startDragAndDrop(clipData,
                                 new View.DragShadowBuilder(view),
                                 null,
                                 flags);
}).attach();

目标活动

Kotlin

// Container where the image is to be dropped in the target app.
val targetImageView = findViewById<ImageView>(R.id.imageView)

targetImageView.setOnDragListener { view, event ->

    when (event.action) {

        ACTION_DROP -> {
            val imageItem: ClipData.Item = event.clipData.getItemAt(0)
            val uri = imageItem.uri

            // Request permission to access the image data being dragged into
            // the target activity's ImageView element.
            val dropPermissions = requestDragAndDropPermissions(event)
            (view as ImageView).setImageURI(uri)

            // Release the permission immediately afterward because it's no
            // longer needed.
            dropPermissions.release()
            return@setOnDragListener true
        }

        // Implement logic for other DragEvent cases here.

        // An unknown action type is received.
        else -> {
            Log.e("DragDrop Example", "Unknown action type received by View.OnDragListener.")
            return@setOnDragListener false
        }

    }
}

Java

// Container where the image is to be dropped in the target app.
ImageView targetImageView = findViewById(R.id.imageView);

targetImageView.setOnDragListener( (view, event) -> {

    switch (event.getAction()) {

        case ACTION_DROP:
            ClipData.Item imageItem = event.getClipData().getItemAt(0);
            Uri uri = imageItem.getUri();

            // Request permission to access the image data being dragged into
            // the target activity's ImageView element.
            DragAndDropPermissions dropPermissions =
                requestDragAndDropPermissions(event);

            ((ImageView)view).setImageURI(uri);

            // Release the permission immediately afterward because it's no
            // longer needed.
            dropPermissions.release();

            return true;

        // Implement logic for other DragEvent cases here.

        // An unknown action type was received.
        default:
            Log.e("DragDrop Example","Unknown action type received by View.OnDragListener.");
            break;
    }

    return false;
});