单个页面多个网络请求的情况（常用总结）

总结1：http://www.cocoachina.com/ios/20170626/19616.html
总结2：http://www.cocoachina.com/ios/20170710/19791.html




dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t serialQueue = dispatch_queue_create( "com.wzb.test.www" , DISPATCH_QUEUE_SERIAL);
    dispatch_group_enter(group);
    dispatch_group_async(group, serialQueue, ^{
        // 网络请求一
        [WebClick getDataSuccess:^(ResponseModel *model) {
            dispatch_group_leave(group);
        } failure:^(NSString *err) {
            dispatch_group_leave(group);
        }];
    });
    dispatch_group_enter(group);
    dispatch_group_async(group, serialQueue, ^{
        // 网络请求二
        [WebClick getDataSuccess:getBigTypeRM onSuccess:^(ResponseModel *model) {
            dispatch_group_leave(group);
        }                                  failure:^(NSString *errorString) {
            dispatch_group_leave(group);
        }];
    });
    dispatch_group_enter(group);
    dispatch_group_async(group, serialQueue, ^{
        // 网络请求三
        [WebClick getDataSuccess:^{
            dispatch_group_leave(group);
        } failure:^(NSString *errorString) {
            dispatch_group_leave(group);
        }];
    });

    // 所有网络请求结束后会来到这个方法
    dispatch_group_notify(group, serialQueue, ^{
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            dispatch_async(dispatch_get_main_queue(), ^{
                // 刷新UI
            });
        });
    });