如何在Objective C中重置计时器？答案

【问题标题】：How to reset a timer in Objective C?如何在Objective C中重置计时器？
【发布时间】：2013-11-26 19:03:45
【问题描述】：

我在这个应用程序中创建了一个计数器，当我单击一个按钮时它会启动，当我单击同一个按钮时它会停止。

问题是当我重新开始时，显示计数的标签不会重置，它会从停止的地方开始计数。

那么任何人都可以帮助我吗？？

- (void)timerTick:(NSTimer *)timer {

_lblCounter.text = @"0:00:00";

double seconds = 0.0;
double minutes = 0.0;
double hours = 0.0;

ticks += 1.0;
seconds = fmod(ticks, 60.0);
minutes = fmod(trunc(ticks / 60.0), 60.0);
hours = trunc(ticks / 3600.0);
_lblCounter.text = [NSString stringWithFormat:@"%2.0f:%02.0f:%02.0f", hours, minutes, seconds];
}


- (IBAction)btnProcessa:(UIButton *)sender {


if ([sender.titleLabel.text isEqualToString:@"Iniciar"]) {

    //Zera contador
    _lblCounter.text = @"0:00:00";

    //Define hora de início
    _startTime = [NSDate date];

    //Exibe hora inicial formatada no Label
    NSString *strHoraInicial = [[self formatter] stringFromDate:_startTime];
    _lblStartTime.text = strHoraInicial;

    //Contador
    timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerTick:) userInfo:nil repeats:YES];

    //Modifica botão
    [sender setTitle:@"Encerrar" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    NSLog(@"Hora de início: %@", strHoraInicial);

 } else {
    //Para contador
    [timer invalidate];

    //Define a hora do encerramento
    NSDate *currentTime = [NSDate date];

    //Exibe hora final formatada no Label
    NSString *strHoraFinal = [[self formatter] stringFromDate:currentTime];
    _lblEndTime.text = strHoraFinal;

    //Calcula a diferença e exibe no Label
    NSTimeInterval elapsedTime = [currentTime timeIntervalSinceDate:_startTime];
    double cost = elapsedTime / 3600.0 * 5.0;
    NSString *valor = [[NSString alloc] initWithFormat:@"R$ %.2f",cost];
    NSLog(@"%@", valor);
    _lblValorPagar.text = valor;
    float fltQtdPessoa = [_txtQtdPessoa.text floatValue];
    float fltValor = cost / fltQtdPessoa;
    NSString *strValor = [[NSString alloc] initWithFormat:@"R$ %.2f", fltValor];
    _lblValorPessoa.text = strValor;

    //Modifica Botão
    [sender setTitle:@"Iniciar" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor colorWithRed:0.208 green:0.710 blue:0.271 alpha:1.000] forState:UIControlStateNormal];

}

}

【问题讨论】：

你在哪里重置计数器（即将ticks设置回0）？
我尝试将 _lblCounter.text 设置为 @"0:00:00"
_blCounter.text（显示）不是滴答声ticks（计数器）。当_lblCounter.text = [NSString stringWithFormat:@"%2.0f:%02.0f:%02.0f", hours, minutes, seconds]; 再次运行时会发生什么？
另外，考虑使用NSDate *timerStartTime（和标准区间数学）并去掉计数器（ticks）。
当我再次运行时，显示屏会继续计数，但不会重置为 0:00:00。如果我使用时间间隔计算，我将如何转换结果，因为它以秒为单位转换为 0:00:00 的格式？通过创建一个 NSFormatter 实例？

标签： ios objective-c nstimer stopwatch

【解决方案1】：

大家好，我通过这样的编码解决了这个问题：

- (void)timerTick:(NSTimer *)timer {

NSDate *strStartTime = timer.userInfo;

NSTimeInterval interval = -[strStartTime timeIntervalSinceNow];
NSLog(@"%.0f", interval);
div_t h = div(interval, 3600);
float hours = h.quot;
div_t m = div(h.rem, 60);
float minutes = m.quot;
float seconds = m.rem;
_lblCounter.text = [[NSString alloc] initWithFormat:@"%2.0f:%02.0f:%02.0f", hours, minutes, seconds];
}



- (IBAction)btnProcessa:(UIButton *)sender {


if ([sender.titleLabel.text isEqualToString:@"Iniciar"]) {

    //Zera contador
    _lblCounter.text = @"0:00:00";

    //Define hora de início
    _startTime = [NSDate date];

    //Exibe hora inicial formatada no Label
    NSString *strHoraInicial = [[self formatter] stringFromDate:_startTime];
    _lblStartTime.text = strHoraInicial;

    //Contador
    contador = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerTick:) userInfo:[NSDate date] repeats:YES];

    //Modifica botão
    [sender setTitle:@"Encerrar" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    NSLog(@"Hora de início: %@", strHoraInicial);

} else {
    //Para contador
    [contador invalidate];

    //Define a hora do encerramento
    NSDate *currentTime = [NSDate date];

    //Exibe hora final formatada no Label
    NSString *strHoraFinal = [[self formatter] stringFromDate:currentTime];
    _lblEndTime.text = strHoraFinal;

    //Calcula a diferença e exibe no Label
    NSTimeInterval elapsedTime = [currentTime timeIntervalSinceDate:_startTime];
    double cost = elapsedTime / 3600.0 * 5.0;
    NSString *valor = [[NSString alloc] initWithFormat:@"R$ %.2f",cost];
    NSLog(@"%@", valor);
    _lblValorPagar.text = valor;
    float fltQtdPessoa = [_txtQtdPessoa.text floatValue];
    float fltValor = cost / fltQtdPessoa;
    NSString *strValor = [[NSString alloc] initWithFormat:@"R$ %.2f", fltValor];
    _lblValorPessoa.text = strValor;

    //Modifica Botão
    [sender setTitle:@"Iniciar" forState:UIControlStateNormal];
    [sender setTitleColor:[UIColor colorWithRed:0.208 green:0.710 blue:0.271 alpha:1.000] forState:UIControlStateNormal];

}

}

【讨论】：