60秒之后重新发送验证码

__block int time = 60;
        __block UIButton *verifybutton = _GetverificationBtn;
        verifybutton.enabled = NO;
        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(time<=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
                    verifybutton.backgroundColor = [UIColor colorWithHexString:@"FC740A"];
                    [verifybutton setTitle:@"获取验证码" forState:UIControlStateNormal];
                    verifybutton.enabled = YES;
                });
            }else{
                dispatch_async(dispatch_get_main_queue(), ^{
                    //设置界面的按钮显示 根据自己需求设置
                    verifybutton.backgroundColor = [UIColor grayColor];
                    NSString *strTime = [NSString stringWithFormat:@"获取验证码(%d)",time];
                    [verifybutton setTitle:strTime forState:UIControlStateNormal];
                    verifybutton.titleLabel.textColor = [UIColor whiteColor];
                });
                time--;
            }
        });
        dispatch_resume(_timer);