1 有时候一个页面有好几个网络请求，而网络请求是异步的，有可能一个请求成功，另一个还在请求，在这个过程中如果刷新UI，可能会造成不好的用户体验以及在导致某些按钮点击无效，下面提供一种方法

创建并发队列，等所有请求结束，刷新UI

_queue = dispatch_queue_create("homeRequest", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t group = dispatch_group_create();

并发队列的特点是
以先进先出的方式，并发调度队列中的任务执行
如果当前调度的任务是同步执行的，会等待任务执行完成后，再调度后续的任务
如果当前调度的任务是异步执行的，同时底层线程池有可用的线程资源，会再新的线程调度后续任务的执行

@interface HomeViewController : BaseViewController
{
     dispatch_queue_t _queue;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self requestUserData:YES pulling:NO];
}

- (void)requestUserData:(BOOL)refresh pulling:(BOOL)pulling {
    if (_queue) {
        return;
    }
    
    BOOL showLoading = NO; // 显示加载框
    
    if (!pulling) {
        if (！数据源1) {
            showLoading = YES;
        }
        
        else if (！数据源2) {
            showLoading = YES;
        }
        else if (！数据源3) {
            showLoading = YES;
        }
    }
    
    if (showLoading) {
        [self showHUDTo:self.view animated:YES];
    }
    
    __weak typeof(self) weakSelf = self;
    _queue = dispatch_queue_create("homeRequest", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t group = dispatch_group_create();
    
    if ([JFUserInfoModel isLogin]) {
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求1]; 
        });
        
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求2]; 
        });
    }
    if (refresh || !_homeAdArray) {
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求3];
        });
    }
    
    if (refresh || !_homeFeatureBannerArray) {
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求4];
        });
    }
    
    if (refresh || !_homeProductBannerArray) {
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求5];
        });
    }
    
    if (refresh || !_homeItemArray) {
        dispatch_group_async(group, _queue, ^{
            [weakSelf 网络请求6];
        });
    }
    if (refresh) {
        // 下拉刷新时
       // do something
    }
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        [weakSelf reload:showLoading pulling:pulling];
    });
}
- (void)reload:(BOOL)showLoading pulling:(BOOL)pulling {
    _queue = nil;
    if (pulling) {
        [_tableView.mj_header endRefreshing];
    }
    else if (showLoading){
        [self hideHUDView:self.view animated:YES]; // 隐藏loading框
    }
    [self setupVenderView];
    [_tableView reloadData];
}

// 网络请求1
- (void) request网络请求1 {
    __block dispatch_semaphore_t sem = dispatch_semaphore_create(0);
    Request *request = [[Request alloc] init];
    [self post:request forResponseClass:[Response class] onSuccess:^(Response *response) {
        if ([response success]) {
            _integral = ((Response *)response).data;
        }
        dispatch_semaphore_signal(sem);
    } onFailure:^(NSError *error) {
        dispatch_semaphore_signal(sem);
    }];
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
}

//  网络请求2
- (void) request网络请求2 {
    __block dispatch_semaphore_t sem = dispatch_semaphore_create(0);
    [self post:request forResponseClass:[indingResponse class] onSuccess:^(Response *response) {
        if ([response success]) {
               [self setupVenderDataWithData:response];
            }
        dispatch_semaphore_signal(sem);
    } onFailure:^(NSError *error) {
        dispatch_semaphore_signal(sem);
    }];
    dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
}