Value of NSString returns null, but unsure why?

问题

I've set the value of my NSString called "fid" to responseObject (see below). responseObject returns the data I want when NSLog'd, but for some reason when I NSLog fid further down, it's empty. Am I missing something? See code:

@property (nonatomic, assign) NSString *fid;

[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!");
    }];

回答1:

You are calling an asynchronous method.

The log statement "further down" is executed long before the fileSave method is completed. The two callbacks of fileSave will be called sometime in the distant future (could be many seconds from now).

Whatever you want to do that needs fid must be done in the completion block of fileSave.

来源：https://stackoverflow.com/questions/29900620/value-of-nsstring-returns-null-but-unsure-why

标签

ios

objective-c

nsstring