iOS中定时器的几种方法 ：
1> [self performSelector:@selector(<#selector#>) withObject:<#(nullable id)#> afterDelay:<#(NSTimeInterval)#>];
2> 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#>
});
3>[NSTimer scheduledTimerWithTimeInterval:<#(NSTimeInterval)#> target:<#(nonnull id)#> selector:<#(nonnull SEL)#> userInfo:<#(nullable id)#> repeats:<#(BOOL)#>];
4> displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(handleDisplayLink:)];
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[displayLink invalidate];
displayLink = nil;
