ios - 如何更正 block 函数 ObjC 中的调度主队列任务？

Question

正在从服务器加载一些数据，但循环(for .. in ..)在实际加载数据之前完成。如何更正主队列上的实现调度或其他错误？

[ApiManager getCategoriesifSuccess:^{
    [self.sectionArray addObjectsFromArray:[CategoryManager getCats]];
    for (CategorySectionModel *mod in [CategoryManager getCats]) {
        [self.arrayForBool addObject:@"YES"];
        [ApiManager getCatalogItemsInCity:currentCity withSection:mod.uid
                                 andStart:@"1" andLimit:@"20" ifSuccess:^{
                                     [self.itemsArray setObject:[CatalogItemManager getItems] forKey:mod.uid];
                                     [indicator stopAnimating];
                                     [self.tableView reloadData];
                                     NSLog(@"DONE WITH SECTION:%@", mod.title);
                                 } orIfFailed:^(NSString *fail) {
                                     NSLog(@"%@", fail);
                                 }];
        NSLog(@"LOOP");
    };
} orIfFailed:^{
}];

控制台返回这个，但它似乎不正确:

2017-12-24 01:17:57.148355+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.149576+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.150786+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.152773+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.154727+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.156987+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.158840+0300 iOS[75679:1805296] LOOP
2017-12-24 01:17:57.981119+0300 iOS[75679:1805296] DONE WITH SECTION:First
2017-12-24 01:17:58.285569+0300 iOS[75679:1805296] DONE WITH SECTION:Second
2017-12-24 01:17:58.403725+0300 iOS[75679:1805296] DONE WITH SECTION:Third
2017-12-24 01:17:58.434170+0300 iOS[75679:1805296] DONE WITH SECTION:Fourth
2017-12-24 01:17:58.449970+0300 iOS[75679:1805296] DONE WITH SECTION:Fifth
2017-12-24 01:17:58.469519+0300 iOS[75679:1805296] DONE WITH SECTION:Sixth
2017-12-24 01:17:58.535116+0300 iOS[75679:1805296] DONE WITH SECTION:Seventh

Answer 1

使用调度组:

Swift(伪代码):

    let group = DispatchGroup()

    for ... {
        group.enter()

        someAsyncMethod({
            group.leave()
        })
    }
    group.notify(queue: DispatchQueue.main, execute: {
        // you code here will be invoked after all group.leave()
    })

确保为每个 group.enter() 只调用一个 (!) group.leave()。如果有失败回调，那么成功和失败回调必须调用group.leave()