安卓开发之通过手势实现图像拖拽功能

/**
 * Android通过手势实现图像拖拽功能
 * @author Administrator
 *
 */
public class DragActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // setContentView(R.layout.main);
        View view = new ImageDragView(this);
       
        setContentView(view);
    }

    class ImageDragView extends View {

        private float x1;
        private float y1;
        private float x2;
        private float y2;

        public ImageDragView(Context context) {
            super(context);
            // TODO Auto-generated constructor stub
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            // TODO Auto-generated method stub

            float size = event.getSize();

            int szi = (int) size;
            int dxi = szi >> 12;
            int dyit = ((1 << 12) - 1);
            int dyi = szi & dyit;

            DisplayMetrics metrics = getResources().getDisplayMetrics();
           
            float dx = metrics.widthPixels * dxi / (float) dyit;
            float dy = metrics.heightPixels * dyi / (float) dyit;

            x1 = event.getX();
            y1 = event.getY();

            x2 = x1 + dx;
            y2 = y1 + dy;

            invalidate();

            return true;
        }

        @Override
        protected void onDraw(Canvas canvas) {
            // TODO Auto-generated method stub
            super.onDraw(canvas);

            float r = (float) Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2)
                    * (y1 - y2)) / 2;
            r = 100 >= r ? 100 : r;

            Paint paint = new Paint();
            paint.setColor(Color.RED);
            canvas.drawCircle(x1, y1, r, paint);
        }
    }