Using NSTimer in a Loop

问题

I need to show a timer counting down from 30 to 0, several times. (30 to 0, start over at 30, etc) However when I placed it in a for-loop, instead of waiting till the timer invalidates to begin the next timer, the loop iterates through and several timers are created.

How can I form a loop that waits until the timer has invalidated?

- (IBAction)startCountdown:(id)sender {

    NSNumber *rounds = [[NSNumber alloc]initWithInt:sliderRounds.value];
    for (int i = rounds.intValue; i > 0; i--) {
        [self timer];
}

回答1:

You can use the scheduledTimerWithTimeInterval

[NSTimer scheduledTimerWithTimeInterval: 0.5
             target: self
             selector: @selector(handleTimer:)
             userInfo: nil
             repeats: NO];

And inside the handleTimer you create the next timer

回答2:

Looks like you are calling some method called 'timer' on self. What does it do? Creates a new timer? Then this is why. When a timer is created, it doesn't block. Instead a method call is scheduled and executed once the timer timeout passes.

回答3:

What you could do is the following:

Create a class that holds an NSTimer
This class would have a variable to hold how many times it needs to count
At the end of one timer (and really, the only one) firing, it decrements the count

You can have the NSTimer repeat by calling it with:

[NSTimer scheduledTimerWithTimeInterval:30.0f
                             target:self 
                           selector:@selector(timerFired)
                           userInfo:nil
                            repeats:YES];

In a method called - (void)timerFired, you would decrement the count. If it reaches zero, you would stop the timer.

Hope this helps!

来源：https://stackoverflow.com/questions/4590524/using-nstimer-in-a-loop

标签

iphone

cocoa-touch

for-loop

nstimer