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 class TouchView extends View {

 private Context mContext;
 private Paint mPaint;
 private Rect mRect;
 private ScaleGestureDetector mScaleGestureDetector;

 public TouchView(Context context) {
  super(context);
  mContext = context;
  mPaint = new Paint();
  mPaint.setColor(Color.BLUE);
  mPaint.setFlags(Paint.ANTI_ALIAS_FLAG);
  mRect = new Rect();
  mRect.left = 10;
  mRect.top = 10;
  mRect.right = 300;
  mRect.bottom = 400;

  mScaleGestureDetector = new ScaleGestureDetector(context, listener);
 }

 OnScaleGestureListener listener = new OnScaleGestureListener() {

  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;
 }
}