iOS：Facebook登录访问令牌错误：由于模拟器错误而退回到从NSUserDefaults加载访问令牌

我按照Facebook iOS SDK指南中的步骤操作,并将Facebook登录按钮放在我的视图控制器中.我显示了NSUserdefaults,其中一个键是“com.facebook.sdk：serverConfiguration”,所以我相信它在那里保存.

- (void)viewDidLoad {
    [super viewDidLoad];
    if ([FBSDKAccessToken currentAccessToken]) {
        // User is logged in,do work such as go to next view controller.
        NSLog(@"test");
    }
    else {
        FBSDKLoginButton *loginButton = [[FBSDKLoginButton alloc] init];
        loginButton.center = self.view.center;
        [self.view addSubview:loginButton];
    }
    _loginButton.readPermissions =
    @[@"public_profile",@"email",@"user_friends"];
    NSLog(@"%@",[[NSUserDefaults standardUserDefaults] DictionaryRepresentation]);
}