谷歌官方笔记之 User Interface

• Drag and Drop [[1] developer.android.com ][Drag and Drop]
  [Drag and Drop]: http://developer.android.com/guide/topics/ui/drag-drop.html "Drag and Drop"
  UML Sequence

UML Sequence

Critical Sectiion

private static class MyDragShadowBuilder extends View.DragShadowBuilder {

        private static Drawable shadow;

        public MyDragShadowBuilder(View v) {
            super(v);
            // Creates a draggable image that will fill the Canvas provided by the system.
            shadow = new ColorDrawable(Color.LTGRAY);
        }
        
        @Override
        public void onProvideShadowMetrics(Point size, Point touch) {
             int width, height;

            // Sets the width of the shadow to half the width of the original View
            width = getView().getWidth() / 2;

            // Sets the height of the shadow to half the height of the original View
            height = getView().getHeight() / 2;

            // The drag shadow is a ColorDrawable. This sets its dimensions to be the same as the
            // Canvas that the system will provide. As a result, the drag shadow will fill the
            // Canvas.
            shadow.setBounds(0, 0, width, height);

            // Sets the size parameter's width and height values. These get back to the system
            // through the size parameter.
            size.set(width, height);

            // Sets the touch point's position to be in the middle of the drag shadow
            touch.set(width / 2, height / 2);
        }

        @Override
        public void onDrawShadow(Canvas canvas) {
            shadow.draw(canvas);
        }
    }

imageView.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
//              ClipData.Item item = new ClipData.Item(v.getTag().toString());
                // Create a new ClipData using the tag as a label, the plain text MIME type, and
                // the already-created item. This will create a new ClipDescription object within the
                // ClipData, and set its MIME type entry to "text/plain"
                ClipData data = ClipData.newPlainText("dot", "Dot : " + v.toString());
                v.startDrag(data, new MyDragShadowBuilder(v), v, 0);
                return false;
            }
        });

  private void processDrop(DragEvent event) {
        final ClipData data = event.getClipData();
        final int N = data.getItemCount();
        for (int i = 0; i < N; i++) {
            ClipData.Item item = data.getItemAt(i);
            Log.i(TAG, "Dropped item " + i + " : " + item);
            String text = item.coerceToText(getContext()).toString();
            if (event.getLocalState() == (Object) this) {
                text += " : Dropped on self!";
            }
        }
    }

Valid DragEvent data by action type

getAction()	getClipDescription()	getLocalState()	getX()	getY()	getClipData()	getResult()
DRAG_STARTED	√	√	√
DRAG_ENTERED	√	√	√	√
DRAG_LOCATION	√	√	√	√
DRAG_EXITED	√	√
ACTION_DROP	√	√	√	√	√
DRAG_ENDED	√	√				√