Facebook iOS SDK有時會爲電子郵件返回空值

我試圖通過我的應用程序登錄來獲取用戶名，Facebook ID和他們的電子郵件。以下是我的應用程序委託：Facebook iOS SDK有時會爲電子郵件返回空值

- (BOOL)openSessionWithAllowLoginUI:(BOOL)allowLoginUI :(FBSessionStateHandler)handler{ 
    NSArray *permissions = [NSArray arrayWithObjects:@"basic_info", @"email", nil]; 
    return [FBSession openActiveSessionWithReadPermissions:permissions allowLoginUI:allowLoginUI completionHandler:handler]; 
}

和我completionHandler代碼和所有在這裏：

void (^fbCompletionHandler)(FBSession *session, FBSessionState state, NSError *error) = ^(FBSession *session, FBSessionState state, NSError *error) { 
    switch (state) { 
     case FBSessionStateOpen: 
      break; 
     case FBSessionStateClosed: 
     case FBSessionStateClosedLoginFailed: 
      [FBSession.activeSession closeAndClearTokenInformation]; 
      break; 
     default: 
      break; 
    } 

    if (error && [FBErrorUtility shouldNotifyUserForError:error]) { 
     NSLog(@"%@", error.localizedDescription); 
     UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Oops" message:[FBErrorUtility userMessageForError:error] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; 
     [alertView show]; 

    } 

    if (session.isOpen) { 
     [[FBRequest requestForMe] startWithCompletionHandler:^(FBRequestConnection *connection, NSDictionary<FBGraphUser> *user, NSError *error) { 
      if (!error) { 
       [self performLoginOperation:user]; 
      } 
     }]; 
    } 
};

，我訪問用戶的電子郵件，像這樣：[user objectForKey:@"email"]。大多數情況下，它可以工作，但是每隔一段時間我就會得到一個nil的價值。我不確定爲什麼因爲我在權限中設置了這麼做？這是否有其他原因？

我試圖鑽進去其他SO帖子，但沒有找到答案：

Facebook SDK email sometimes returns null - Android

Facebook SDK 3.0: how to receive user's e-mail?

PHP SDK 3.1.1 getUser() sometimes return 0

來源

2013-08-27 KVISH