第一步:声明手势对象,并加入你想要作用的view上
// 放大缩小手势
UIPinchGestureRecognizer *pinchRecognizer = [[UIPinchGestureRecognizer alloc]
initWithTarget:self action:@selector(scale:)];
[pinchRecognizer setDelegate:self];
[self.view addGestureRecognizer:pinchRecognizer];
[pinchRecognizer release];