创建定时器

 (1) NSTimer创建定时器：
@property (nonatomic, strong) NSTimer *timer;

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.timer = [NSTimer timerWithTimeInterval:0.5 target:self selector:@selector(updateTimer) userInfo:nil repeats:YES];
        [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
        [self.timer fire];
    }
    return self;
}
- (void)updateTimer {
    NSLog(@"定时器计时开始");
}
- (void)cleanTimer {
    [self.timer invalidate];
    //self.timer = nil;
}

 (2)CADisplayLink创建定时器：
@property (nonatomic, strong)CADisplayLink *displayLink;

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(updateTime)];
        self.displayLink.frameInterval = 0.5;
        [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
    }
    return self;
}
- (void)updateTime {
    NSLog(@"定时器计时开始");
}
- (void)cleanTimer {
    [self.displayLink invalidate];
}

(3) dispatch_source_t创建定时器：
@property (nonatomic, strong) dispatch_source_t timer;

- (instancetype)init
{
    self = [super init];
    if (self) {
        count = 0;
        self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
        dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC));
        uint64_t interval = (uint64_t)(1.0 * NSEC_PER_SEC);
        dispatch_source_set_timer(self.timer, start, interval, 0);
        //设置事件处理回调
        dispatch_source_set_event_handler(self.timer, ^{
            NSLog(@"定时器计时开始");
        });
        //启动定时器
        dispatch_resume(self.timer);
    }
    return self;
}
- (void)cleanTimer {
    if (self.timer) {
        dispatch_source_cancel(self.timer);
        //self.timer = nil;
    }
}