Facebook iOS SDK 3.2重新打开会话总是失败

Question

基本上我浏览了这个页面并实现了我的Facebook登录。

https://developers.facebook.com/docs/howtos/login-with-facebook-using-ios-sdk/

接下来，当用户再次打开应用程序时，我尝试重新打开会话：

[appDelegate openSessionWithAllowLoginUI:NO];

//The method is:

- (BOOL)openSessionWithAllowLoginUI:(BOOL)allowLoginUI {
    NSArray *permissions = [[NSArray alloc] initWithObjects:
        @"email", 
        @"user_likes",
        nil];
    return [FBSession openActiveSessionWithReadPermissions:permissions
                                              allowLoginUI:allowLoginUI
                                         completionHandler:^(FBSession *session,
                                                         FBSessionState state,
                                                         NSError *error) {
                                         [self sessionStateChanged:session
                                                             state:state
                                                             error:error];
                                     }];
}

但是FBSessionState总是0：

/*! One of two initial states indicating that no valid cached token was found */
    FBSessionStateCreated                   = 0,

我尝试了几乎所有东西，使用FBSessionTokenCachingStrategy存储和恢复tokendata，但没有一个工作。如果我打电话

[appDelegate openSessionWithAllowLoginUI:YES];

并在会话开始时显示LoginUI，但我不希望每次都显示LoginUI。你能救我吗？