Android通过手势实现的缩放处理实例代码

 class MultiTouchView extends View {

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

  public MultiTouchView(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 = 50 >= r ? 50 : r;

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

  }

 }

}