使用dispatch_group_t 解决多个接口协调调用问题

 dispatch_group_t group =dispatch_group_create();

    dispatch_group_enter(group);

    dispatch_async(dispatch_get_global_queue(0,0), ^{

        self.arr_DB = [[SearchHistoryDBgetInstance] getAllData];

        dispatch_group_leave(group);

    });

    dispatch_group_enter(group);

    dispatch_async(dispatch_get_global_queue(0,0), ^{

        [ClassHttpToolrmssSearchWithSuccess:^(NSArray *arr) {

            self.arr_RM = [arrmutableCopy];

            dispatch_group_leave(group);

        } failure:^(NSInteger code,NSString *desc) {

            dispatch_group_leave(group);

        }];

    });

    dispatch_group_notify(group,dispatch_get_main_queue(), ^{

        NSLog(@"任务完成");

        [selfdrawHeaderView];

    });