xcode (NSTimer) 创建一个计时器倒计时

(NSTimer) creating a Timer Countdown

提问by Matthew Nieuwenhuys

I am trying to create a simple Countdown Timer so that when a player enters my game the timer begins from 60 down to 0. It seems simple but I am getting confused at how I write this.

我正在尝试创建一个简单的倒数计时器，以便当玩家进入我的游戏时，计时器从 60 开始到 0。这看起来很简单，但我对如何编写此内容感到困惑。

So far I have created a method within my GameController.m that looks like this:

到目前为止，我已经在我的 GameController.m 中创建了一个如下所示的方法：

-(int)countDownTimer:(NSTimer *)timer {
    [NSTimer scheduledTimerWithTimeInterval:-1
                                 invocation:NULL
                                    repeats:YES];
    reduceCountdown = -1;
    int countdown = [[timer userInfo] reduceCountdown];
    if (countdown <= 0) {
        [timer invalidate];
    }
    return time;
}

At the start of the game I initialise the integer Time at 60. The label is then being set within ViewController. But at the moment when I compile the code it just shows the label at 60 and doesn't decrement at all.

在游戏开始时，我将整数 Time 初始化为 60。然后在 ViewController 中设置标签。但是在我编译代码的那一刻，它只是在 60 处显示标签，并且根本没有减少。

Any help would be greatly appreciated - I am new to Objective-C.

任何帮助将不胜感激 - 我是 Objective-C 的新手。

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EDIT

编辑

With some assistance from I have now separated the code into 2 separate methods. The code now looks like this:

在我的帮助下，我现在已将代码分成 2 个单独的方法。代码现在看起来像这样：

-(void)countDown:(NSTimer *)timer {
    if (--time == 0) {
        [timer invalidate];
        NSLog(@"It's working!!!");
    }
}

-(void)countDownTimer:(NSTimer *)timer {
    NSLog(@"Hello");
    [NSTimer scheduledTimerWithTimeInterval:1
                                      target:self
                             selector:@selector(countDown:)
                                      userInfo:nil
                                      repeats:YES];
}

HOWEVER, the code is still not running properly and when I call the method [game countDownTimer] from my View Controller it breaks saying: "unrecognized selector sent to instance". Can anybody explain what is wrong here?

但是，代码仍然无法正常运行，当我从我的视图控制器调用方法 [game countDownTimer] 时，它会中断说：“无法识别的选择器发送到实例”。任何人都可以解释这里有什么问题吗？

回答by dasblinkenlight

Several things are wrong with your code:

您的代码有几处错误：

• You are passing a wrong parameter for the time interval- negative numbers are interpreted as the 0.1 ms
• You are calling the wrong overload- you are expected to pass an invocation object, yet you are passing a NULL
• You put the code that you want executed on timer together with timer initialization- the code that needs to be executed on timer should go into a separate method.

• 您为时间间隔传递了错误的参数- 负数被解释为 0.1 ms
• 您正在调用错误的重载- 您应该传递一个调用对象，但您传递的是一个NULL
• 您将要在计时器上执行的代码与计时器初始化放在一起- 需要在计时器上执行的代码应该放在一个单独的方法中。

You should call the overload that takes a selector, and pass 1for the interval, rather than -1.

您应该调用带有选择器的重载，并传递1间隔，而不是-1.

Declare NSTimer *timerand int remainingCounts, then add

声明NSTimer *timerand int remainingCounts，然后添加

timer = [NSTimer scheduledTimerWithTimeInterval:1
                                         target:self
                                       selector:@selector(countDown)
                                       userInfo:nil
                                        repeats:YES];
remainingCounts = 60;

to the place where you want to start the countdown. Then add the countDown method itself:

到要开始倒计时的地方。然后添加 countDown 方法本身：

-(void)countDown {
    if (--remainingCounts == 0) {
        [timer invalidate];
    }
}

回答by bbarnhart

Try this

尝试这个

- (void)startCountdown
{
    _counter = 60;

    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1
                                                      target:self
                                                    selector:@selector(countdownTimer:)
                                                    userInfo:nil
                                                     repeats:YES];
}

- (void)countdownTimer:(NSTimer *)timer
{
    _counter--;
    if (_counter <= 0) { 
        [timer invalidate];
        //  Here the counter is 0 and you can take call another method to take action
        [self handleCountdownFinished];
   }
}

回答by Tirupathi Raju

From the question you posed.you can achieve that by invoking a function for every 1 sec and handle the decrement logic in that.

从您提出的问题来看，您可以通过每 1 秒调用一个函数并处理其中的递减逻辑来实现这一点。

Snippet:-

片段：-

NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 1.0
                      target: self
                      selector:@selector(onTick:)
                      userInfo: nil repeats:YES];
(void)onTick
{
   //do what ever you want
   NSLog(@"i am called for every 1 sec");
//invalidate after 60 sec [timer invalidate];
}