Android implements the method of making pictures move arbitrarily on the screen (drag and drop function)

public class DragExampleActivity extends Activity {
  Bitmap mBitmap;
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    (savedInstanceState);
    mBitmap = (getResources(), );
    setContentView(new DragView(this));
  }
  @Override
  protected void onDestroy()
  {
    ();
    if(null != mBitmap) {
      ();
      mBitmap = null;
    }
  }
  private class DragView extends View {
    private int mMotionX = 0;
    private int mMotionY = 0;
    private Paint paint;
    public DragView(Context context)
    {
      super(context);
      paint = new Paint();
    }
    @Override
    public void draw(Canvas canvas)
    {
      (canvas);
      (mBitmap, mMotionX, mMotionY, paint);
    }
    @Override
    public boolean onTouchEvent(MotionEvent ev)
    {
      if(() == MotionEvent.ACTION_DOWN)
      {
        mMotionX = (int) ();
        mMotionY = (int) ();
        invalidate();
        return true;
      }else {
        return (ev);
      }
    }
  }
}