ios - 如何从 block 内部修改非局部(全局)变量？

Question

我是 Objective-C 的新手，必须动态更改

的值 <code>@property (strong, nonatomic) NSMutableArray *allCategories</code>

来自AFHTTPRequestOperationManager内部在 success阻止。
[self.allCategories addObject:tempObject];
不改变allCategories的值在循环中迭代。

变量已初始化为
self.allCategories = [[NSMutableArray alloc]init];
在 vi​​ewDidLoad 中。

我也试过创建一个临时变量 <code>__block NSMutableArray *tempCategories = [[NSMutableArray alloc]init];</code>在开始之前AFHTTPRequestOperationManager目的。 tempCategories甚至不保留它的值(value)。

无法弄清楚发生了什么。

编辑
抱歉给您带来的不便
viewDidLoad 有以下代码< br/> self.allCategories = [[NSMutableArray alloc]init];
[self loadData];

这是代码

-(NSMutableArray *)loadData
{
    __block NSMutableArray *tempCategories = [[NSMutableArray alloc]init];

    manager = [AFHTTPRequestOperationManager manager];

    [manager GET:kAPICategoryList
      parameters:nil
         success:^(AFHTTPRequestOperation *operation, id responseObject) {

             // downcast id to NSMutableDictionary
             NSMutableDictionary *json = (NSMutableDictionary *)responseObject;

             // check if dictionary is non nil has at least 1 element
             if (json != nil && [json count] >= 1) {

                 // NSLog(@"json:\t%@", json);

                 // check json is non nil & has success message
                 if ([json objectForKey:kAPIKeyCategoryRoot] != nil) {

                     NSArray *arrCategoriesRoot = [json objectForKey:kAPIKeyCategoryRoot];

                     // check categories has some data
                     if (arrCategoriesRoot.count >= 1) {

                         for (int i = 0; i < arrCategoriesRoot.count; i++) {

                             SomeModel *pCategory;

                             NSDictionary *dctCategorySingle = [arrCategoriesRoot objectAtIndex:i];

                             // check category has sub category
                             if ([dctCategorySingle objectForKey:kAPIKeyCategorySubCategory] != nil) {
                                 // create category with sub category
                                 pCategory = [[SomeModel alloc]initWithSubCategorisedCategoryID:[dctCategorySingle objectForKey:kAPIKeyCategoryID]
                                                                                              name:[dctCategorySingle objectForKey:kAPIKeyCategoryName]
                                                                                             image:kIMGCategoryDefault
                                                                                       subCategory:[dctCategorySingle objectForKey:kAPIKeyCategorySubCategory]];
                             } else{
                                 // create just a category
                                 pCategory = [[SomeModel alloc]initWithCategoryID:[dctCategorySingle objectForKey:kAPIKeyCategoryID]
                                                                                name:[dctCategorySingle objectForKey:kAPIKeyCategoryName]
                                                                               image:kIMGCategoryDefault];
                             } // else just
                             [tempCategories addObject:pCategory];
                             [_allCategories addObject:pCategory];
                         } // for
                         NSLog(@"categories count %lu", [self.allCategories count]);
                     } // if count >= 1
                 }
                 else if ([json objectForKey:kAPIRespMsgCategoryFetchErrKey] != nil) {
                     [Utility showAlertWithTitle:kAPIRespMsgCategoryFetchErrKey
                                         message:[json objectForKey:kAPIRespMsgCategoryFetchErrVal]
                                          button:kMsgButtonOkayTtl];
                 }
             } else {
                 // error in login => enable login
                 NSLog(@"%@", kMsgNetworkEmptyJSON);
             }
         }
     // network error
         failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSLog(@"error %@", [error localizedDescription]);
         }];
    NSLog(@"tempCategories count %lu", [tempCategories count]);
    return tempCategories;
}

这是 NSLog 的输出形式:

2015-03-19 18:27:17.845 MyProject[4011:121268] viewDidLoad
2015-03-19 18:27:18.133 MyProject[4011:121268] tempCategories 计数 0
2015-03-19 18:27:18.136 MyProject[4011:121268] numberOfRowsInSection 计数 0
2015-03-19 18:27:18.137 MyProject[4011:121268] numberOfRowsInSection 计数 0
2015-03-19 18:27:19.019 MyProject[4011:121268] 类别计数 20

当 loadData 时finishes allCategories 中没有数据(无)。

Answer 1

据我所知，它应该以这种方式工作。您确定在检查 allCategories 的内容之前调用了成功 block 吗？

success block 异步工作，这意味着它只会在 RequestOperation 完成时执行(如果您正在下载大文件，这可能需要很长时间)

如果您试图在执行成功 block 之前获取allCategories 的值，您将无法获得预期的结果。我建议在您的成功 block 上使用断点或 NSLog 来查看它是否在您认为它正在执行时执行。

例如

 ...
 successBlock:^(AFHTTPRequestOperation *operation, id responseObject)
 {
     NSLog(@"Success");
     [self.allCategories addObject:tempObject]
  }]; //End of request

[operation start]; //Begin executing the AFHTTPOperation

NSLog("%@",self.allCategories.description); //probably nil or empty
//since the success block hasn't been called yet  

编辑:

尽管如此，您要返回一个值之前由异步操作设置，要从异步操作返回一个值，我建议您查看此 answer和 this一 。您还应该阅读一些异步任务的工作原理。

基本上，您想要对异步操作/任务执行的操作是确保该值在您想要使用时可用。这样做的主要问题是您不知道何时该值将被设置，但您可以确定什么您想要在设置时执行什么。

为此，您可以创建一个带有自定义完成 block 的简单方法

- (void)myCustomMethodWithCompletionBlock: (void (^)(NSArray *))completion {
   //Do your request
   //...
   successBlock:^(AFHTTPRequestOperation *operation, id responseObject)
  {
      NSLog(@"Success");
      completionBlock(allCategories);
   }]; //End of request
}

同时在您调用的主要方法中

 [self myCustomMethodWithCompletionBlock:^(NSArray *allCategories) {
    self.allCategories = allCategories;
    //Do other stuff you need to with that variable since now you are
    //sure the value will be set unless the operation failed
   }];