NSTimer 的最小有效时间间隔是多少？

Question

我想用NSTimer增加标签上显示的数字。

这是我的代码：

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

self.numberLabel = [[UILabel alloc]initWithFrame:CGRectMake(90, 90, 90, 30)];
[self.view addSubview:self.numberLabel];


self.timer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(refreshText) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop]addTimer:self.timer forMode:NSRunLoopCommonModes];
}

- (void)refreshText{

NSDate *beginDate = [NSDate date];

static NSInteger a = 0;
a ++;

self.numberLabel.text = [NSString stringWithFormat:@"%ld",a];

if (a == 1000) {

    NSDate *endDate = [NSDate date];

    NSTimeInterval durationTime = [endDate timeIntervalSinceDate:beginDate];
    NSTimeInterval intervalTime = self.timer.timeInterval;

    NSLog(@"durationTime = %f",durationTime);
    NSLog(@"intervalTime = %f",intervalTime);

    [self.timer invalidate];
    self.timer = nil;
} 
}

控制台显示：

然后我把定时器的timeInterval从0.01改成0.001，控制台显示：

迷惑的是为什么timeInterval为0时durationTime不是0.0000056。001.What另外，NSTimer的timeInterval有没有最小值可以设置？

Answer 1

NSTimer 的时间段是 NSTimeInterval 类型的值，而这提供了 sub-millisecond precision that does not help you. From the start of the NSTimer documentation:

Timers work in conjunction with run loops. Run loops maintain strong references to their timers, so you don’t have to maintain your own strong reference to a timer after you have added it to a run loop.

To use a timer effectively, you should be aware of how run loops operate. See Threading Programming Guide for more information.

A timer is not a real-time mechanism. If a timer’s firing time occurs during a long run loop callout or while the run loop is in a mode that isn't monitoring the timer, the timer doesn't fire until the next time the run loop checks the timer. Therefore, the actual time at which a timer fires can be significantly later. See also Timer Tolerance.

因此 NSTimer 的最小时间间隔与运行循环迭代的长度相关。虽然内部优化（如果存在）可以在设置后立即触发计时器，但如果间隔真的很小，一般来说，您将获得的最短时间取决于运行循环迭代的剩余执行时间设置了哪个定时器，这对于通用编程来说几乎是不确定的。

如果您真的需要高分辨率计时器（请参阅@bbum 对您的问题的评论），那么您需要研究该主题 - 只需搜索“高分辨率”之类的内容timing macOS”作为起点。

HTH

Answer 2

有更好的方法来解决您的问题。使用 CADisplayLink 而不是 NSTimer。 CADisplayLink 允许您在每次屏幕刷新时更新 UI - 尽可能快。更新 UI 频率超过屏幕刷新频率是没有意义的，因此 NSTimer 不是快速 UI 更新的最佳工具。

func beginUpdates() {
  self.displayLink = CADisplayLink(target: self, selector: #selector(tick))    
  displaylink.add(to: .current, forMode: .defaultRunLoopMode)
}

func tick() {
  // update label
}

func endUpdates(){
  self.displayLink.invalidate()
  self.displayLink = nil
}

NSTimer 的最小有效时间间隔是多少？

What's the minimum valid time interval of an NSTimer?

ios

objective-c

nstimer