实现短信倒计时

@implementation ForgetViewController {
    
    __strong NSTimer * timer;
    NSInteger          secondes;
    
    
}
- (void)dealloc{
    
    if(timer != nil){
        [timer invalidate];
        timer = nil;
    }
}



secondes= 59;
                if (!timer) {
                    timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerFired:) userInfo:nil repeats:YES];
                    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
                    [timer fire];


-(void)timerFired:(id) sender
{
    if(secondes <=0) {
        self.codeBtn.enabled = YES;
        [self.codeBtn setTitle:@"重新获取" forState:UIControlStateNormal];
    } else {
        NSString * title = [NSString stringWithFormat:@"(%lds)后重发", secondes];
        [self.codeBtn setTitle:title forState:UIControlStateNormal];
    }
    secondes--;
}