实现多点触摸缩放图片

从android2.2开始引入了一个ScaleGestureDetector类，可以用来实现多点触摸缩放图片。 
ScaleGestureDetector detector ; 
ImageView imageView; 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
        imageView = (ImageView) findViewById(R.id.imageView1); 
        detector = new ScaleGestureDetector(this, listener); 
    } 
    private OnScaleGestureListener listener = new OnScaleGestureListener() { 
Matrix matrix = new Matrix(); 
@Override 
public void onScaleEnd(ScaleGestureDetector detector) { 

} 

@Override 
public boolean onScaleBegin(ScaleGestureDetector detector) { 
return true; 
} 
//记得在该方法中使用getScaleFactor方法，在onscaleEnd方法中得到的值基本都是1 
@Override 
public boolean onScale(ScaleGestureDetector detector) { 
float factor = detector.getScaleFactor(); 
matrix.setScale(factor,factor); 
imageView.setImageMatrix(matrix); 
return false; 
} 
}; 
public boolean onTouchEvent(android.view.MotionEvent event) { 
return detector.onTouchEvent(event); 
}