Improved Drag-Drop for an Android GridView

(March 4, 2013 Updsate: This example has been revised for Android V4, See Drag-Drop for GridView V4.)

I have an improved version of my tutorial app described in “Drag-Drop for an Android GridView“. It allows a drag-drop sequence to be initiated from any touch event. The earlier version required the user to do a long click (press) before dragging would start.

Download this demo application here: download from Wglxy.com. It was built with API level 8. Be sure to do a “Clean” rebuild in Eclipse.

Changes

This example application, like other ones I have done related to drag-drop, was based on the Android Launcher code. The Launcher required a long click (press) before an icon on the home screen could be dragged. Several people asked how to make it work on just a regular click. I finally got around to doing that.

To do this, all I had to do was make the activity implement View.onTouchListener. The handler  checks for the ACTION_DOWN event that indicates that the user touched the screen. If it sees that, it starts a drag operation.

public boolean onTouch (View v, MotionEvent ev)
{
 // If we are configured to start only on a long click,
 // we are not going to handle any events here.
 if (mLongClickStartsDrag) return false;
 boolean handledHere = false;
 final int action = ev.getAction();
 // In the situation where a long click is not needed
 // to initiate a drag, simply start on the down event.
 if (action == MotionEvent.ACTION_DOWN) {
    handledHere = startDrag (v);
 }

 return handledHere;
}

There is no right answer for the question: what starts a drag operation? It’s really your choice: long click or one touch. So what I did in the demo application is put a new variable into the DragActivity class. It indicates whether you want long clicks to be the only way to start a drag-drop operation.

private boolean mLongClickStartsDrag = false;
    // If true, it takes a long click to start the drag operation.
    // Otherwise, any touch event starts a drag.

So you can try out both ways of starting a drag-drop operation. Just change the value of the variable from false to true.

References

Input Events – describes the different types of input events for views: click events, touch events, etc.

Discussion about the touch events – the end of the note has a succinct statement about the differences