NSTimer的准确性 [英] Accuracy of NSTimer

问题描述

我正在尝试使用NSTimer创建一个秒表样式的计时器，该计时器每0.1秒递增一次，但有时似乎运行得太快..

I am trying to use NSTimer to create a Stop-watch style timer that increments every 0.1 seconds, but it seems to be running too fast sometimes ..

这是我的操作方式:

Timer =[NSTimer scheduledTimerWithTimeInterval: 0.1 target:self selector:@selector(updateTimeLabel) userInfo:nil repeats: YES];

然后:

-(void)updateTimeLabel
{
    maxTime=maxTime+0.1;
    timerLabel.text =[NSString stringWithFormat:@"%.1f Seconds",maxTime];
}

这将在Label中显示计时器的值，以后我可以将maxTime用作计时器停止的时间...

This will display the value of the timer in the Label, and I can later utilize maxTime as the time when the Timer is stopped ...

问题是它运行不准确.

有没有一种方法可以确保NSTimer每0.1秒准确触发一次?我知道NSTimer是不准确的，并且我要进行调整以使其准确.

Is there a method where I can make sure that NSTimer fires strictly every 0.1 seconds accurately ? I know that NSTimer isn't accurate , and I'm asking for a tweak to make it accurate.

谢谢

推荐答案

以下是您可以用来做您想做的事情的类:

Here's a class you can use to do what you want:

@interface StopWatch()
@property ( nonatomic, strong ) NSTimer * displayTimer ;
@property ( nonatomic ) CFAbsoluteTime startTime ;
@end

@implementation StopWatch

-(void)dealloc
{
    [ self.displayTimer invalidate ] ;
}

-(void)startTimer
{
    self.startTime = CFAbsoluteTimeGetCurrent() ;
    self.displayTimer = [ NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector( timerFired: ) userInfo:nil repeats:YES ] ;
}

-(void)stopTimer
{
    [ self.displayTimer invalidate ] ;
    self.displayTimer = nil ;

    CFAbsoluteTime elapsedTime = CFAbsoluteTimeGetCurrent() - self.startTime ;
    [ self updateDisplay:elapsedTime ] ;
}

-(void)timerFired:(NSTimer*)timer
{
    CFAbsoluteTime elapsedTime = CFAbsoluteTimeGetCurrent() - self.startTime ;
    [ self updateDisplay:elapsedTime ] ;
}

-(void)updateDisplay:(CFAbsoluteTime)elapsedTime
{
    // update your label here
}

@end

关键点是:

1. 通过将秒表启动时的系统时间保存到变量中来进行计时.
2. 秒表停止时，通过从当前时间中减去秒表开始时间来计算经过的时间
3. 使用计时器更新您的显示.无论您的计时器是否准确，这都不重要.如果您要保证至少每隔0.1秒更新一次显示，则可以尝试将计时器间隔设置为最小更新时间(0.05s)的1/2.

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