count down using button and NSTimer

gistfile1.txt

- (void)startTimer
{
    self.leftSecondsNum = 59;
    self.fetchCodeBtn.enabled = NO;
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(refreshCountNum) userInfo:nil repeats:YES];
    [self.fetchCodeBtn setTitle:[NSString stringWithFormat:@"重新获取(%ld)", (long)self.leftSecondsNum] forState:UIControlStateDisabled];
}

- (void)endupTimer
{
    [self.timer invalidate];
    self.timer = nil;
    self.fetchCodeBtn.enabled = YES;
}

- (void)refreshCountNum
{
    self.leftSecondsNum -= 1;
    if (self.leftSecondsNum < 0) {
        [self endupTimer];
        return;
    }
    [self.fetchCodeBtn setTitle:[NSString stringWithFormat:@"重新获取(%ld)", (long)self.leftSecondsNum] forState:UIControlStateDisabled];
}