一：dispatch_after
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t) (<#delayInSeconds#> * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
<#code to be executed after a specified delay#>
});
二：NSObject中提供的线程延迟方法
[self performSelector:@selector(run) withObject:nil afterDelay:2.0];
三：通过NSTimer来延迟线程执行
[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(run) userInfo:nil repeats:NO];
