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 = [[SearchHistoryDB
getInstance] getAllData];
        dispatch_group_leave(group);
    });
    dispatch_group_enter(group);
    dispatch_async(dispatch_get_global_queue(0,
0), ^{
        [ClassHttpTool
rmssSearchWithSuccess:^(NSArray *arr) {
            self.arr_RM = [arr
mutableCopy];
            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");
        [self
drawHeaderView];
    });