倒計時UILabel沒有減少

Question

我正在嘗試制作一個倒計時標簽，但它沒有減少。可以在代碼中找出任何一個錯誤

- (IBAction)start:(id)sender
{
     timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self   selector:@selector(updateCountdown) userInfo:nil repeats: YES];
}

-(void) updateCountdown
{
     int hours, minutes, seconds;
     int secondsLeft = 30;
     hours = secondsLeft / 3600;
     minutes = (secondsLeft % 3600) / 60;
     seconds = (secondsLeft %3600) % 60;
     countDownlabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
}

Answer 1

因為每次定時器觸發時你都使用相同的值為秒int secondsLeft=30;

您必須在啟動Timer時設置secondsLeft的值，並在計時器上遞減它

- (IBAction)start:(id)sender{

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

  secondsLeft=30;
 }

 -(void) updateCountdown {
    int hours, minutes, seconds;

    secondsLeft--;
    hours = secondsLeft / 3600;
    minutes = (secondsLeft % 3600) / 60;
    seconds = (secondsLeft %3600) % 60;
    countDownlabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];

Answer 2

您可以將secondsLeft和timer聲明為ivars，每次調用updateCountdown遞減secondsLeft ，並在沒有剩余秒數遞減時使timer無效。

- (IBAction)start:(id)sender
{
    secondsLeft = 30;
    timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self   selector:@selector(updateCountdown) userInfo:nil repeats: YES];
}

- (void) updateCountdown
{
    int hours, minutes, seconds;

    hours = secondsLeft / 3600;
    minutes = (secondsLeft % 3600) / 60;
    seconds = (secondsLeft %3600) % 60;
    countDownlabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
    secondsLeft--;

    if (seconds==0)
    {
        [timer invalidate];
    }
}

Answer 3

你已經分配了int secondsLeft=30; 在你的updateCountdown方法中，這是正常的。

你應該在其他地方設置secondLeft的初始值，然后在你的方法updateCountdown你需要遞減它的值

 -(void) updateCountdown {
    int hours, minutes, seconds;

    hours = secondsLeft / 3600;
    minutes = (secondsLeft % 3600) / 60;
    seconds = (secondsLeft %3600) % 60;
    countDownlabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];
    if (secondsLeft > 0) secondsLeft--;
}

Answer 4

我發現了問題......

-(IBAction)start:(id)sender{


countDownView.hidden=NO;

timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(updateElapsedTime) userInfo:nil repeats:YES];
secondsLeft=30;

}



 -(void) updateCountdown {
int hours, minutes, seconds;


hours = secondsLeft / 3600;
minutes = (secondsLeft % 3600) / 60;
seconds = (secondsLeft %3600) % 60;
countDownlabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hours, minutes, seconds];

}