给手势UITapGestureRecognizer添加"tag"标志

UITapGestureRecognizer是没有tag属性，但他有UIView的属性，我们可以通过给UIView添加tag属性，从而标记UITapGestureRecognizer。

UITapGestureRecognizer *singleTap =
[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(whenClickImage:)];
[_firstImage addGestureRecognizer:singleTap];
UIView *singleTapView = [singleTap view];
singleTapView.tag = 0;
[singleTap release];

-(void)whenClickImage:(id)sender
{
UITapGestureRecognizer *singleTap = (UITapGestureRecognizer *)sender;
NSLog(@"%d",[singleTap view].tag]);
}