MrNickBarker が提案したように、解決策はユーザーを SSO からログアウトすることです。ただし、これを行うと、ユーザーが iOS 6 認証システムを介して再度ログインすることが絶対に確実である場合にのみ、これを実行したかったのです。
私の問題は、ユーザーが設定アプリを介して Facebook にログインしていることを確認する方法を知らなかったことです。ユーザーを Facebook からログアウトさせて、Facebook アプリに送り返してもらいたくありませんでした。毎回の SSO ログイン。
ACAccountStore メソッドのどれも、ユーザーが Facebook の詳細を設定アプリに入力したかどうかを教えてくれません。
ここに解決策があります：
ACAccountStore *accountStore = [[NSClassFromString(@"ACAccountStore") alloc] init];
ACAccountType *accountType;
if (accountStore &&
(accountType = [accountStore accountTypeWithAccountTypeIdentifier:@"com.apple.facebook"]) &&
[SLComposeViewController isAvailableForServiceType:SLServiceTypeFacebook])
{
// There's an account store and it knows about Facebook - we must be on iOS 6 or higher.
//
// [SLComposeViewController isAvailableForServiceType:SLServiceTypeFacebook] also tells us that
// the user has signed into their Faecbook account via the Settings app.
//
// At this point there could be a valid session that's been previously created via SSO prior to the
// user signing into Facebook from Settings.app. In this case, calling openActiveSessionWithReadPermissions:
// will continue to log on using SSO rather than the preferred route of using the built in iOS support.
//
// [accountStore accountsWithAccountType:accountType] will return an account for this application once
// it's been used to log into Facebook. Clearly, if there is an account returned then the then we don't want to
// force a logout.
//
// On the other hand, if no accounts are returned then we can safely call closeAndClearTokenInformation
// in order to clear any SSO tokens, thereby ensuring that the next login will attempt to use the iOS
// authentication (which we can do since the user has signed into the Settings app).
if ([[accountStore accountsWithAccountType:accountType] count] == 0)
[FBSession.activeSession closeAndClearTokenInformation];
// Try to connect with read permissions only (as required for iOS auth)
_usingiOSIntegratedLogin = YES;
[FBSession openActiveSessionWithReadPermissions:nil
allowLoginUI:YES
completionHandler:completionHandler];
}
else
{
// Either this is < iOS 6, or there's no Facebook account registered - request both
// read and write permissions in order to avoid two trips to the Facebook app or web view
_usingiOSIntegratedLogin = NO;
NSMutableArray *permissions = [NSMutableArray arrayWithArray:[self publishPermissions]];
[permissions insertObject:@"user_photos" atIndex:0];
[FBSession openActiveSessionWithPermissions:permissions
allowLoginUI:YES
completionHandler:completionHandler];
}