不断收到无法分配的错误

Question

在下面的函数中，我不断得到：

Variable is not assignable (missing __block type specifier)

我尝试通过将 __block 添加到 twitterUsername 来修复它，然后添加 returns null 函数。我究竟做错了什么？我真的很想了解这背后的逻辑，而不仅仅是解决方案。

- (NSString *) getTwitterAccountInformation
{
    ACAccountStore *accountStore = [[ACAccountStore alloc] init];
    ACAccountType *accountType = [accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierTwitter];

    NSString *twitterUsername = [[NSString alloc] init];

    [accountStore requestAccessToAccountsWithType:accountType 
                                          options:nil 
                                       completion:^(BOOL granted, NSError *error) 
    {
        if(granted) {
            NSArray *accountsArray = [accountStore accountsWithAccountType:accountType];

            if ([accountsArray count] > 0) {
                ACAccount *twitterAccount = [accountsArray objectAtIndex:0];
                NSLog(@"%@",twitterAccount.username);
                NSLog(@"%@",twitterAccount.accountType);

                twitterUsername = [NSString stringWithFormat:@"%@", twitterAccount.username];
            }
        }
    }];

    NSLog(@"Twitter username is: %@", twitterUsername);

    return twitterUsername;
}

Answer 1

requestAccessToAccountsWithType:options:completion: 方法是异步的，这意味着它不等待对网络调用的响应，returns 立即。相反，它会在调用返回后排队执行一个块，并在加载数据后执行它。

一个可能的解决方案是让您的 getTwitterAccountInformation 也将完成块作为参数，它可能看起来像这样：

- (void) getTwitterAccountInformation:(void(^)(NSString *userName, NSError *error))completion
{
    ACAccountStore *accountStore = [[ACAccountStore alloc] init];
    ACAccountType *accountType = [accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierTwitter];

    [accountStore requestAccessToAccountsWithType:accountType options:nil completion:^(BOOL granted, NSError *error) {
        if(error) {
             completion(nil, error);
        }
        if(granted) {
            NSArray *accountsArray = [accountStore accountsWithAccountType:accountType];

            if ([accountsArray count] > 0) {
                ACAccount *twitterAccount = [accountsArray objectAtIndex:0];
                NSLog(@"%@",twitterAccount.username);
                NSLog(@"%@",twitterAccount.accountType);

                NSString *twitterUsername = twitterAccount.username;
                NSLog(@"Twitter username is: %@", twitterUsername);
                completion(twitterUsername, nil);
            }
        }
    }];
}

不断收到无法分配的错误

Keep getting unassignable error

ios

objective-c

twitter