直接上代码

//设置发送验证码倒计时
- (void)resendCheckCodeBtnMode
{
    __block int timeout=60; //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
                [_checkCodeBtn setTitle:@"重新发送" forState:UIControlStateNormal];
                [_checkCodeBtn setTitleColor:[UIColor colorWithHex:@"#6C6C6C"] forState:UIControlStateNormal];
                //_checkCodeBtn.contentEdgeInsets = UIEdgeInsetsMake(12, 23, 12, 23);
                [_checkCodeBtn setBackgroundColor:[UIColor colorWithHex:@"#FFD700"]];
                _checkCodeBtn.userInteractionEnabled = YES;
            });
        }else{
            NSString *strTime = [NSString stringWithFormat:@"%.2d", timeout];
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                [_checkCodeBtn setTitle:[NSString stringWithFormat:@"获取验证码(%@)",strTime] forState:UIControlStateNormal];
                [_checkCodeBtn setTitleColor:[UIColor colorWithHex:@"#FFD700"] forState:UIControlStateNormal];
               // _checkCodeBtn.contentEdgeInsets = UIEdgeInsetsMake(12, 5, 12, 5);
                [_checkCodeBtn setBackgroundColor:[UIColor whiteColor]];
                _checkCodeBtn.userInteractionEnabled = NO;
            });
            timeout--;
        }
    });
    dispatch_resume(_timer);
}