- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { NSLog(@"----touchesBegan"); static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ // NSLog(@"----once"); 只会打印一次 NSLog(@"----once"); }); }
原文：http://www.cnblogs.com/nxz-diy/p/5365684.html