获取短信验证码

__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
            [_veryfyBtn setTitle:@"获取验证码" forState: UIControlStateNormal];
            _veryfyBtn.enabled = YES;
        });
    }else{
        //                        int minutes = timeout / 60;
        //                        int seconds = timeout % 60;
        NSString *strTime = [NSString stringWithFormat:@"倒计时%d秒",timeout];
        dispatch_async(dispatch_get_main_queue(), ^{
            //设置界面的按钮显示 根据自己需求设置
            _veryfyBtn.enabled = NO;
            _veryfyBtn.backgroundColor = LightLGray;
            [_veryfyBtn setTitle:strTime forState: UIControlStateDisabled];
        });
        timeout--;
    }
});
dispatch_resume(_timer);