1.performSelector
[self performSelector:@selector(doSomeThing) withObject:self afterDelay:2];
/**
* 延迟执行
*
* @param aSelector 方法名称
* @param anArgument 要传递的参数，如果无参数，就设为nil
* @param delay 延迟的时间
*/
- (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay{}
2.GCD
int64_t delayInSeconds = 10.0; // 延迟的时间
/*
*@parameter 1,时间参照，从此刻开始计时
*@parameter 2,延时多久，此处为秒级，还有纳秒等。10ull * NSEC_PER_MSEC
*/
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// do something
});
3.每一秒执行一次 （重复性）
[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(testTimer) userInfo:nil repeats:YES];
