Can't use NSTimer update UI

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0

In my app, I want to use a NSTimer update my UIButton instance, but my button's title didn't change as the time elapse. My code is here:

-(void)fireTimer{

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

    [self.timer fire];
}

- (void)timerAction
{
    self.leftTime--;
    NSLog(@"%d current runloop and mode is %@", self.leftTime, [NSRunLoop currentRunLoop].currentMode);

    [self.customBtn setTitle:[NSString stringWithFormat:@"leftTime:%d", self.leftTime] forState:UIControlStateNormal];

    if(self.leftTime == 0)
    {
        [self.timer invalidate];
    }
}

And the NSLog output is correct:

Can someone tell me what's the problem? thanks!

asked 28 secs ago

billwang1990

92