Facebook iOS 选择好友表空白

我正在尝试将“选择的朋友”添加到我的 iOS 应用程序中。我设置了登录视图。登录后，我打开朋友选择器，但它显示为空白。我看到带有“完成”和“取消”按钮的表，但表中没有加载任何朋友。

- (IBAction)selectFriendsButtonAction:(id)sender {
    if (self.friendPickerController == nil) {
        // Create friend picker, and get data loaded into it.
        self.friendPickerController = [[FBFriendPickerViewController alloc] init];
        self.friendPickerController.title = @"Select Friends";
        self.friendPickerController.delegate = self;
    }
    [self.friendPickerController loadData];
    [self.friendPickerController clearSelection];
    [self presentViewController:self.friendPickerController animated:YES completion:nil];

}

在打开朋友选择器控制器之前，请通过调用以下命令确保您的 Facebook 会话处于活动状态：

if (!FBSession.activeSession.isOpen) {
    // if the session is closed, then we open it here, and establish a handler for state changes
    [FBSession.activeSession openWithCompletionHandler:^(FBSession *session,
                                                         FBSessionState state,
                                                         NSError *error) {
        // Handle error
    }];
}