no delay achieved with NSTimer

问题

I want to delay between each output result for say, 1 second. The code below is not delaying but is processing correctly. Why is it not delaying between each dealCard?

- (IBAction)startPause
{
    if ([self.deal length]>cardNum) {
        timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:@selector(dealCard) userInfo:nil repeats:NO];
        [timer fire];
    }
}


- (void) dealCard{
    card.text = [NSString stringWithFormat:@"%i",cardNum+1];
    cardTo.text = [self.deal substringWithRange:(NSRange){(cardNum+self.randCut)%[self.cardList count],1}];
    cardNum=cardNum + 1;
    [self startPause];
}

回答1:

According to the documentation fire "Causes the receiver’s message to be sent to its target." Which is why it's firing instantly.

Your timer is also not scheduled, so it would never fire on it's own.

Create your timer like this instead, which creates a timer, and schedules it in a single statement.

timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                         target:self
                                       selector:@selector(dealCard)
                                       userInfo:nil
                                        repeats:NO];

And remove the [timer fire] line completely, as it will fire itself after it's time interval is up.

来源：https://stackoverflow.com/questions/17055297/no-delay-achieved-with-nstimer