求大神帮忙啊！Android用手势缩放图片的时候图片变黑

源码：
public boolean onFling(MotionEvent event1, MotionEvent event2, float velocityX,
float velocityY) {
// TODO Auto-generated method stub
velocityX=velocityX>4000?4000:velocityX;
velocityX=velocityX<-4000?-4000:velocityX;
currentScale+=currentScale*velocityX/4000.0f;
currentScale=currentScale>0.01?currentScale:0.01f;
matrix.reset();
matrix.setScale(currentScale,currentScale,160,200);
BitmapDrawable tmp=(BitmapDrawable)iv.getDrawable();
if(!tmp.getBitmap().isRecycled()){
tmp.getBitmap().recycle();
}
Bitmap bitmap=Bitmap.createBitmap(image,0,0,width,height,matrix,true);
iv.setImageBitmap(bitmap);
return true;
}
轻击后第一次出现缩图片的样式，第二次就会变黑。。。。。顺便请问我们一般“放大”手势的缩放是怎么写的...?