隐藏Facebook授权对话框iPhone

[[NSUserDefaults standardUserDefaults] setObject:_facebook.accessToken forKey:@\"FBAccessToken\"];
[[NSUserDefaults standardUserDefaults] setObject:_facebook.expirationDate forKey:@\"FBExpirationDate\"];
[[NSUserDefaults standardUserDefaults] synchronize];

    if ( [[NSUserDefaults standardUserDefaults] objectForKey:@\"FBAccessToken\"] != nil ) {
        _facebook.accessToken = [[NSUserDefaults standardUserDefaults] objectForKey:@\"FBAccessToken\"];
        _facebook.expirationDate = [[NSUserDefaults standardUserDefaults] objectForKey:@\"FBExpirationDate\"];
    }