更改用户输入Facebook WP8

Question

所以我在facebooksdk.net上使用了这段代码

private async void PublishStory()
{
    await this.loginButton.RequestNewPermissions("publish_stream");

    var facebookClient = new Facebook.FacebookClient(this.loginButton.CurrentSession.AccessToken);

    var postParams = new
    {
        name = "Facebook SDK for .NET",
        caption = "Build great social apps and get more installs.",
        description = "The Facebook SDK for .NET makes it easier and faster to develop Facebook integrated .NET apps.",
        link = "http://facebooksdk.net/",
        picture = "http://facebooksdk.net/assets/img/logo75x75.png"
    };

    try
    {
        dynamic fbPostTaskResult = await facebookClient.PostTaskAsync("/me/feed", postParams);
        var result = (IDictionary<string, object>)fbPostTaskResult;

        Dispatcher.BeginInvoke(() =>
        {
            MessageBox.Show("Posted Open Graph Action, id: " + (string)result["id"], "Result", MessageBoxButton.OK);
        });
    }
    catch (Exception ex)
    {
        Dispatcher.BeginInvoke(() =>
        {
            MessageBox.Show("Exception during post: " + ex.Message, "Error", MessageBoxButton.OK);
        });
    }
}

当我点按发布按钮时，它会共享预设链接，如何将其更改为用户输入文本框？我不想使用系统facebook，因为我正在建立一个Facebook客户端