ScaleGestureDetector使用注意事项

注：一定要通过view的onTouchEvent调用mScaleGestureDetector.onTouchEvent(ev);，只有这样

才能调用回调函数：onScaleBegin

具体可以参加：android源码：KenBurnsActivity.java

下面是转载的文章：

Detects transformation gestures involving more than one pointer ("multitouch") using the supplied MotionEvents.

 TheScaleGestureDetector.OnScaleGestureListener callback will notify users when a particular gesture event has occurred. This class should only be used with MotionEvents reported via touch. To use this class:

• Create an instance of the ScaleGestureDetector for your View
• In the (View's )onTouchEvent(MotionEvent) method ensure you call (ScaleGestureDetector's )onTouchEvent(MotionEvent). The methods defined in your callback will be executed when the events occur.

下面是测试的代码：

   public void onScaleEnd(ScaleGestureDetector detector) {
    // TODO Auto-generated method stub
    Log.i("OnScaleGestureListener", "onScaleEnd");
   }

   public boolean onScaleBegin(ScaleGestureDetector detector) {
    // TODO Auto-generated method stub
    Log.i("OnScaleGestureListener", "onScaleBegin detector.getCurrentSpan() = " + detector.getCurrentSpan());
    detector.getCurrentSpan();
    return true;
   }

   public boolean onScale(ScaleGestureDetector detector) {
    // TODO Auto-generated method stub
    float cur = detector.getCurrentSpan();
    float pre = detector.getPreviousSpan();
    float cp = cur - pre;
    Log.i("OnScaleGestureListener", "onScale detector.getCurrentSpan() = " + cur
      + " detector.getPreviousSpan() = " + pre
      + " cur - pre = " + (cur - pre));
    if (cp < -100 && !mScaled) {
     mScaled = true;
     mRect.left = 10+ 50;
     mRect.top = 10 + 50;
     mRect.right = 300 - 50;
     mRect.bottom = 400 - 50;
     invalidate();
    } else if (cp > 100 && mScaled) {
     mScaled = false;
     mRect.left = 10;
     mRect.top = 10 ;
     mRect.right = 300 ;
     mRect.bottom = 400;
     invalidate();
    }
    return false;
   }
  };

  boolean mScaled = false;
  /*@Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   int widthMode = MeasureSpec.getMode(widthMeasureSpec);
   int width = MeasureSpec.getSize(widthMeasureSpec);
   int heightMode = MeasureSpec.getMode(heightMeasureSpec);
   int height = MeasureSpec.getSize(heightMeasureSpec);
   super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  }*/



  @Override
  protected void onDraw(Canvas canvas) {
   canvas.drawRect(mRect, mPaint);
  }



  @Override
  public boolean onTouchEvent(MotionEvent event) {
   System.out.println("event.getPointerCount() : " + event.getPointerCount());
   mScaleGestureDetector.onTouchEvent(event);
   return true;
  }
 }