ios短信驗證碼倒計時功能

上代碼

-(void)calcTime{
    __block int timeout=60;
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒執行
    dispatch_source_set_event_handler(_timer, ^{
        if(timeout<=0){ //倒計時結束，關閉
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //設置界面的按鈕顯示 根據本身需求設置
                [_verifyButton setBackgroundImage:[UIImage imageNamed:@"resend_icon.png"] forState:UIControlStateHighlighted];
                [_verifyButton setBackgroundImage:[UIImage imageNamed:@"resend_selected_icon.png"] forState:UIControlStateSelected];
                _verifyButton.userInteractionEnabled = YES;

                self.seconds.hidden=YES;
                self.secondBackgroundPic.hidden=YES;
                self.secondSymbol.hidden=YES;
            });
        }else{
            int seconds = timeout % 60;
            NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];
            dispatch_async(dispatch_get_main_queue(), ^{
                [UIView beginAnimations:nil context:nil];
                [UIView setAnimationDuration:1];
                self.seconds.text=[NSString stringWithFormat:@"%@",strTime];
                [UIView commitAnimations];
                _verifyButton.userInteractionEnabled = NO;
            });
            timeout--;
        }
    });
    dispatch_resume(_timer);
    
    
}