Objective c 用于ios单例实现的新facebook sdk

我已经更新了新的FacebookSDK（3.1），并尝试将其集成到我以前使用的singleton类中。我的代码：

-(void)postFacebook {
    if ([FBSession.activeSession isOpen]) {
        [[AAFacebook sharedInstance] postToWallWithScreenshot];
    } else {
        [[AAFacebook sharedInstance] openSessionWithAllowLoginUI:YES];
    }
}

以及公开会议方法：

- (BOOL)openSessionWithAllowLoginUI:(BOOL)allowLoginUI {

    return [FBSession openActiveSessionWithReadPermissions:nil
                                              allowLoginUI:allowLoginUI
                                         completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {
                                             [self sessionStateChanged:session state:state error:error];
                                         }];
}



- (void)sessionStateChanged:(FBSession *)session
                      state:(FBSessionState)state
                      error:(NSError *)error
{
    NSLog(@"Is FBSession opened? A: %i", FBSession.activeSession.isOpen);

    switch (state) {

        case FBSessionStateOpen: {

            NSLog(@"Login succesfully & post to FaceBook!");

        }
            break;
        case FBSessionStateClosed: {
            [FBSession.activeSession closeAndClearTokenInformation];
        }
            break;
        case FBSessionStateClosedLoginFailed: {
            NSLog(@"FaceBook login failed.");
        }
            break;

        default:
            break;
    }

    [[NSNotificationCenter defaultCenter] postNotificationName:kAAFacebookNoficationChanged
                                                        object:session];

}

现在，如果我第二次尝试共享，我会遇到以下错误：

2013-01-07 10:28:26.894[2098:907] Error: HTTP status code: 400
2013-01-07 10:28:26.904[2098:907] Photo uploaded failed :( {
    "com.facebook.sdk:HTTPStatusCode" = 400;
    "com.facebook.sdk:ParsedJSONResponseKey" =     {
        body =         {
            error =             {
                code = 2500;
                message = "An active access token must be used to query information about the current user.";
                type = OAuthException;
            };
        };
        code = 400;
    };
}

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你知道如何处理访问令牌吗？

我终于知道了。似乎FB SDK为我处理会话令牌