objective-c - NSMutableDictionary 中的 setValue forKey 崩溃

Question

我有如下代码。我正在从 Web 服务器检索 JSON。

AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON)
                                     {    

                                         for (NSMutableDictionary * dataDict in JSON) {


                                             if ([dataDict objectForKey:@"userPicture"])
                                             {

                                                objectForKey:@"userPicture"]);
                                                 NSURL *url = [NSURL URLWithString:[dataDict objectForKey:@"userPicture"]];
                                                 UIImage *image = [UIImage imageWithData: [NSData dataWithContentsOfURL:url]];     


                                                 [dataDict setValue:@"userPicture"
                                                             forKey:@"userPicture"]; 


                                             } 


                                             [messageList addObject: dataDict];
                                         }                                             

                                         [self processComplete];

                                     } 
                                    failure:^(NSURLRequest *request , NSURLResponse *response , NSError *error , id JSON)
                                     {
                                         NSLog(@"Failed: %@", error);        

                                     }];

但是它崩溃并出现以下错误:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'

现在，我不明白的是，我正在尝试 setValue:forKey在dataDict中，实例化 NSMutableDictionary ，所以我应该能够设置值。

Answer 1

您已将 dataDict 声明为 NSMutableDictionary ，但这并不意味着您从 JSON 中获得了可变字典。您可以做的是指示您的 JSON 序列化程序获取可变副本(如果它支持此类选项)或手动执行此操作:

for (NSDictionary *dict in JSON) {

    NSMutableDictionary * dataDict = [dict mutableCopy];
    // Rest of the code here...

}