init方法中的异步

Question

我想在ModelUser init中创建一个异步方法。来自Parse会话的ModelUser init _userId：

-(id)init{
    self = [super init];
    if (self) {
        sqlUserModelImpl = [[UserModelSql alloc] init];
        parseUserModelImpl = [[UserModelParse alloc] init];
        sqlGroupModelImpl = [[GroupModelSql alloc] init];
        parseGroupModelImpl = [[GroupModelParse alloc] init];
        modelUserGroupImpl = [[ModelUserGroup alloc] init];
        sqlUserGroupModelImpl = [[UsersGroupsRelationShipSql alloc] init];
        parseUserGroupModelImpl = [[UsersGroupsRelationshipParse alloc] init];
        _user = [self getCurrentUser];
    }
    return self;
}

如果用户从上一个会话连接，登录控制器会调用ModelUser Instance来登录应用程序：

if ([ModelUser instance].user != nil) {

        NSLog(@"username and password were correct");

        //init next controller
        UIStoryboard* sb = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        screenController* nVC = [sb
                                 instantiateViewControllerWithIdentifier:@"screenController"];

        NSString* userId=[[ModelUser instance] getCurrentUser];
            NSLog(@"userId Logged = %@",userId);
            nVC.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
            [self showViewController:nVC sender:self];

    }

问题是制作异步＆＃34; getCurrentUser＆＃34;因为init方法返回＆＃34; self＆＃34;在_user参数获取Id之前。然后，我回到登录控制器nil而不是getCurrentUser结果