-(void)startTime{        __block int timeout=120; //倒计时时间    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); //每秒执行    dispatch_source_set_event_handler(_timer, ^{        if(timeout<=0){ //倒计时结束，关闭            dispatch_source_cancel(_timer);            dispatch_async(dispatch_get_main_queue(), ^{                //设置界面的按钮显示 根据自己需求设置                [self.sendAuthCode setTitle:@"发送验证码" forState:UIControlStateNormal];                self.sendAuthCode.userInteractionEnabled = YES;                self.sendAuthCode.titleLabel.font = [UIFont systemFontOfSize:10];            });        }else{                        int seconds = timeout % 120;            NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];            dispatch_async(dispatch_get_main_queue(), ^{                //设置界面的按钮显示 根据自己需求设置                [self.sendAuthCode setTitle:[NSString stringWithFormat:@"%@秒后重发",strTime] forState:UIControlStateNormal];                self.sendAuthCode.titleLabel.font = [UIFont systemFontOfSize:10];                self.sendAuthCode.userInteractionEnabled = NO;                            });            timeout--;                    }    });    dispatch_resume(_timer);    }