NSString 的值 returns 为 null，但不确定为什么？

Question

我已将名为 "fid" 的 NSString 的值设置为 responseObject（见下文）。 responseObject returns NSLog 时我想要的数据，但由于某种原因，当我 NSLog 进一步向下查找时，它是空的。我错过了什么吗？见代码：

.h

@property (nonatomic, assign) NSString *fid;

.m

[DIOSFile fileSave:file success:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"File uploaded!");

    [file setObject:[responseObject objectForKey:@"fid"] forKey:@"fid"];
    [file removeObjectForKey:@"file"];

 fid = [responseObject objectForKey:@"fid"];
        NSLog(@"%@",responseObject);

 } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
     NSLog(@"Failed to upload file!");
  }];

    NSDictionary *bodyValues = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:_itemDescrip.text, nil] forKeys:[NSArray arrayWithObjects:@"value", nil]];
    NSDictionary *languageDict = [NSDictionary dictionaryWithObject:[NSArray arrayWithObject:bodyValues] forKey:@"und"];
    [nodeData setObject:languageDict forKey:@"body"];

    [nodeData setObject:@"storage_item" forKey:@"type"];

    NSMutableDictionary *dict = [NSMutableDictionary dictionary];

    [dict setObject: [NSString stringWithFormat:@"%@", fid] forKey:@"fid"];
    NSLog(@"%@", fid);

    NSDictionary *fidLangDict = [NSDictionary dictionaryWithObject:[NSArray arrayWithObject:dict] forKey:@"und"];

    [nodeData setObject:fidLangDict forKey:@"field_photo"];

    [DIOSNode nodeSave:nodeData success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSLog(@"Node saved!");


    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Node did not save!");
    }];

Answer 1

您正在调用一个异步方法。

日志语句"further down"在fileSave方法完成之前很久就被执行了。 fileSave 的两个回调将在遥远的未来某个时候被调用（可能是从现在开始的许多秒）。

无论你想做什么，都必须在 fileSave 的完成块中完成。

NSString 的值 returns 为 null，但不确定为什么？

Value of NSString returns null, but unsure why?

objective-c

nsstring

ios