导航到另一个视图后重置 NSTimer [英] Reset NSTimer after navigating to another view

问题描述

目前我正在开发一个需要秒表的游戏，比如 1 分钟，当用户点击播放按钮时，它进入游戏屏幕，我希望运行秒表倒计时 1 分钟 01:00,00:59,00:58 等原因，我搜索并发现 NSTimer 将是实现秒表的理想选择.因此我拿了一个标签，创建了一个 NSTimer 实例，分配了时间间隔并开始递减计时器标签中的值，即:

Currently I am developing a game which needs a stop watch say 1 minute,when user taps the play button it enters the game screen,I want the to run the stop watch count down of 1 minute 01:00,00:59,00:58 etc. For that reason I searched and found NSTimer would be the ideal choice to implement a stop watch.Hence I took a label,created an instance of NSTimer,assigned time interval and started decrementing the value in timer label,i.e.:

-(void)viewDidAppear:(BOOL)animated
{
    self.stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(viewWillAppear:) userInfo:nil repeats:YES];
    [super viewDidAppear:YES];
}

-(void)viewWillAppear:(BOOL)animated
{
    static int currentTime = 60;
    int newTime = currentTime--;
    int minutesRemaining = newTime / 60; // integer division, truncates fractional part
    int secondsRemaining = newTime % 60; // modulo division

    self.timerLabel.text = [NSString stringWithFormat:@"%02d:%02d", minutesRemaining, secondsRemaining];

    if ([self.timerLabel.text isEqualToString:@"00:00"])
    {
        [stopWatchTimer invalidate];
    }
    [super viewWillAppear:YES];
}

这里的问题是计时器从 01:00,00:59,00:58 开始运行并继续运行，比如说在第 53 秒，我导航到另一个视图并返回，它从 00:53,00 开始运行:52 等等，但我希望它从 01:00 开始运行，为此我在 viewDidDisappear 中实现了无效的 NSTimer ie

The problem here is the timer starts running 01:00,00:59,00:58 and goes on,say at 53rd second,I navigated to another view and came back,it is running from 00:53,00:52 and so on,but I want it to run from 01:00 and for that I implemented invalidating NSTimer in viewDidDisappear i.e.

-(void)viewDidDisappear:(BOOL)animated
{
    if ([stopWatchTimer isValid])
    {
        [stopWatchTimer invalidate];
        self.stopWatchTimer = nil;
    }
    [super viewDidDisappear:YES];
}

仍然存在同样的问题！

对该问题进行了大量研究，但没有找到有用且有效的答案.

Done lots of Research on the issue and found no answer useful and working.

有人可以指导我吗，任何帮助表示赞赏.

Can some one please guide me,any help is appreciated.

提前谢谢大家:)

推荐答案

您正在使用选择器 viewWillAppear 作为计时器.viewWillAppear 是 viewController 上的一个方法，当视图出现在屏幕上时会被调用，你不应该自己调用它.相反，创建自己的方法来减少计时器:

You are use the selector viewWillAppear for the timer. viewWillAppear is a method on a viewController that gets called when the view appears on screen, you should not call it yourself. Instead, create your own method that decrements the timer:

-(void)viewDidAppear:(BOOL)animated
{
  [super viewDidAppear:animated];
  self.stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateTime:) userInfo:nil repeats:YES];
  currentTime = 60; // This could be an instance variable
  self.timerLabel.text = @"01:00";
}


-(void)updateTime {
  int newTime = currentTime--;
  int minutesRemaining = newTime / 60; // integer division, truncates fractional part
  int secondsRemaining = newTime % 60; // modulo division

  self.timerLabel.text = [NSString stringWithFormat:@"%02d:%02d", minutesRemaining, secondsRemaining];

  if ([self.timerLabel.text isEqualToString:@"00:00"])
  {
      [self.stopWatchTimer invalidate];
  }
}

-(void)viewDidDisappear:(BOOL)animated
{
 [super viewDidDisappear:animated];
  if ([self.stopWatchTimer isValid])
  {
    [self.stopWatchTimer invalidate];
    self.stopWatchTimer = nil;
  }
}

使用这种技术，计时器负责每秒调用一次，但您可能会在几秒钟后遇到计时问题.为了获得更准确的计时，您应该存储开始倒计时的时间，然后在每次 updateTime 调用时，将当前时间与存储的开始时间进行比较.

With this technique the timer is responsible for calling every second, but you will probably have timing issues after some seconds. To have a more accurate timing, you should store the time that you started the countdown and then on every updateTime call, compare the current time with the stored started time.

添加到您的界面:

@property (nonatomic) NSTimeInterval startTime;

然后在实现中:

-(void)viewDidAppear:(BOOL)animated
{
    self.startTime = [NSDate timeIntervalSinceReferenceDate];
    self.duration = 60; // How long the countdown should be
    self.stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:0.1
                                                           target:self
                                                         selector:@selector(updateTime)
                                                         userInfo:nil
                                                          repeats:YES];
    self.timerLabel.text = @"01:00"; // Make sure this represents the countdown time
}

-(void)updateTime {

  int newTime = self.duration - (round([NSDate timeIntervalSinceReferenceDate] - self.startTime));
  int minutesRemaining = newTime / 60; // integer division, truncates fractional part
  int secondsRemaining = newTime % 60; // modulo division

  self.timerLabel.text = [NSString stringWithFormat:@"%02d:%02d", minutesRemaining, secondsRemaining];

  if (newTime < 1)
  {
    [self.stopWatchTimer invalidate];

    /* Do more stuff here */

  }
}

-(void)viewDidDisappear:(BOOL)animated
{
 [super viewDidDisappear:animated];
  if ([self.stopWatchTimer isValid])
  {
    [self.stopWatchTimer invalidate];
    self.stopWatchTimer = nil;
  }
}

对代码的一些额外(无关)注释:

Some extra (unrelated) comments on the code:

在实现 viewDidDisappear: 时将 animated 参数传递给对 super 的调用:[super viewDidDisappear:animated];在实现 viewDidAppear: 时，将 animated 参数传递给 super 的调用，另外，请确保在方法中先调用 super this，然后再执行其他操作

when implementing viewDidDisappear: pass the animated parameter to the call to super: [super viewDidDisappear:animated]; when implementing viewDidAppear: pass the animated parameter to the call to super, also, make sure you call super first this in the method, before doing anything else

这篇关于导航到另一个视图后重置 NSTimer的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！