iOS 几种定时方式

1. //第一种 每一秒执行一次（重复性）  
2. double delayInSeconds = 1.0;  
3. timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0));  
4. dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC, 0.0);  
5. dispatch_source_set_event_handler(timer, ^{  
6.     NSLog(@"timer date 1== %@",[NSDate date]);  
7. });  
8. dispatch_resume(timer);  
9.   
10. //第二种 二秒后执行 （一次性）  
11. double delayInSeconds = 2.0;  
12. dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));  
13. dispatch_after(popTime, dispatch_get_main_queue(), ^(void){  
14.     NSLog(@"timer date 2== %@",[NSDate date]);  
15. });  
16.   
17. //第三种 每一秒执行一次 （重复性）  
18. [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(testTimer) userInfo:nil repeats:YES];