NSTimer不准，scheduleTimer放在runloop里面，受runloop模式影响会不准
// [NSTimer scheduledTimerWithTimeInterval:<#(NSTimeInterval)#> target:<#(nonnull id)#> selector:<#(nonnull SEL)#> userInfo:<#(nullable id)#> repeats:<#(BOOL)#>];
所以创建GCD定时器
//dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, <#dispatchQueue#>);
//dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, <#intervalInSeconds#> * NSEC_PER_SEC, <#leewayInSeconds#> * NSEC_PER_SEC);
//dispatch_source_set_event_handler(timer, ^{
// <#code to be executed when timer fires#>
//});
// [NSTimer scheduledTimerWithTimeInterval:<#(NSTimeInterval)#> target:<#(nonnull id)#> selector:<#(nonnull SEL)#> userInfo:<#(nullable id)#> repeats:<#(BOOL)#>];
所以创建GCD定时器
//dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, <#dispatchQueue#>);
//dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, <#intervalInSeconds#> * NSEC_PER_SEC, <#leewayInSeconds#> * NSEC_PER_SEC);
//dispatch_source_set_event_handler(timer, ^{
// <#code to be executed when timer fires#>
//});
//dispatch_resume(timer);
看下面实例：
#import "ViewController.h"@interface ViewController ()
/** 定时器（这里不用带*，因为dispatch_source_t就是个类，内部包含了） */
@property (nonatomic, strong) dispatch_source_t timer;
@end@implementation ViewController- (void)viewDidLoad {[super viewDidLoad];//获得队列dispatch_queue_t dispatchQueue = dispatch_get_global_queue(0, 0);//创建一个gcd定时器 (dispatch_source_t timer:dispatch_source_t本质还是个OC对象，是个局部变量，需要强引用，不然下面使用无效)self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatchQueue);//OC对象%@可以打印NSLog(@"%@", self.timer);//设置定时器的各种属性（几时开始，每隔多长时间执行一次）//GCD时间参数，一般是纳秒 NSEC_PER_SEC 纳秒单位等于一秒；DISPATCH_TIME_NOW当前时间dispatch_time_t start = DISPATCH_TIME_NOW;uint64_t interval = (uint64_t)(2.0 *NSEC_PER_SEC);dispatch_source_set_timer(self.timer, start, interval, 0);dispatch_source_set_event_handler(self.timer, ^{NSLog(@"--------%@",[NSThread currentThread]);});//启动定时器dispatch_resume(self.timer);
}-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {NSLog(@"----touchesBegan点击取消定时器!");dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{//取消定时器dispatch_cancel(self.timer);self.timer = nil;NSLog(@"%@",self.timer);});
}
@end实例可直接使用，可以封装成timer类使用，懂了的请点赞哦！！！
)
