Android 拖放问题不显示

我正在开发一个拖放应用程序，一切正常，但我看到了一个问题。我有 3 个 ImageView，其中两个是可拖动对象，另一个是放置目标。每次我将物体扔到除放置目标之外的任何位置时，它都会完全消失！

下面是我使用的代码：

       ImageView iv1, iv2, iv3;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    initControls();

}

private void initControls() {
    // TODO Auto-generated method stub

    iv1 = (ImageView) findViewById (R.id.imageView1);
    iv2 = (ImageView) findViewById (R.id.imageView2);

    iv1.setTag("a");
    iv2.setTag("b");

    iv3 = (ImageView) findViewById (R.id.imageView3);
    iv1.setOnTouchListener(new MyTouchListener());
    iv2.setOnTouchListener(new MyTouchListener());
    iv3.setOnDragListener(new MyDragListener());

}

private final class MyTouchListener implements OnTouchListener {
    public boolean onTouch(View view, MotionEvent motionEvent) {
      if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
        ClipData data = ClipData.newPlainText("", "");
        DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
        view.startDrag(data, shadowBuilder, view, 0);
        view.setVisibility(View.INVISIBLE);
        return true;
      } else {
        return false;
      }
    }
}

class MyDragListener implements OnDragListener {
    //Drawable enterShape = getResources().getDrawable(R.drawable.shape_droptarget);
    //Drawable normalShape = getResources().getDrawable(R.drawable.shape);

    @Override
    public boolean onDrag(View v, DragEvent event) {
      switch (event.getAction()) {
      case DragEvent.ACTION_DRAG_LOCATION:
          if(v != iv3)
              v.setVisibility(View.VISIBLE);
        break;
      case DragEvent.ACTION_DRAG_STARTED:
        // Do nothing
        break;
      case DragEvent.ACTION_DRAG_ENTERED:

        break;
      case DragEvent.ACTION_DRAG_EXITED:

        break;
      case DragEvent.ACTION_DROP:

        // Dropped, reassign View to ViewGroup
        //handle the dragged view being dropped over a drop view
        View view = (View) event.getLocalState();

        Drawable dropshadow = getResources().getDrawable(R.drawable.dropshadow);

        //view dragged item is being dropped on
        ImageView dropTarget = (ImageView) v;

        //view being dragged and dropped
        ImageView dropped = (ImageView) view;

        /*
        //if an item has already been dropped here, there will be a tag
        Object tag = dropTarget.getTag();

        //if there is already an item here, set it back visible in its original place
        if(tag!=null)
        {
            //the tag is the view id already dropped here
            int existingID = (Integer)tag;
            //set the original view visible again
            findViewById(existingID).setVisibility(View.VISIBLE);

        }

        //set the tag in the target view to the ID of the view being dropped
        dropTarget.setTag(dropped.getId());
        */


              String temp = "a";
              if(temp.equals(view.getTag())){
                  //dropped.setBackground(dropshadow);
                  dropTarget.setBackground(dropshadow);
                  Log.d(temp, "Correct Image");
              } else {
                  Log.d("b", "Wrong Image");
                  view.setVisibility(View.VISIBLE);
              }



        break;
      case DragEvent.ACTION_DRAG_ENDED:

      default:
        break;
      }
      return true;
    }
}

我在这里缺少什么？非常感谢任何帮助。谢谢。

最后我自己解决了这个问题。我添加了这个方法：

 private boolean dropEventNotHandled(DragEvent dragEvent) {
            return !dragEvent.getResult();
}

并添加了这个：

 case DragEvent.ACTION_DRAG_ENDED:
           if (dropEventNotHandled(event)) 
              view.setVisibility(View.VISIBLE);
        break;