bit.ly API で URL を短縮する

public class UrlShortenerBase
{
    public virtual string Shorten(string longUrl) { return string.Empty; }
    public virtual string Expand(string shortUrl) { return string.Empty; }
    protected virtual string ApiUrl { get { return string.Empty; } }
 
    protected string GetRestUrl(string command)
    {
        return ApiUrl + command;
    }
 
    protected static string WebGet(string url, NameValueCollection parameters)
    {
        Encoding enc = Encoding.UTF8;
        WebClient wc = new WebClient();
        wc.QueryString = parameters;
 
        byte[] result = wc.DownloadData(url);
        string data = enc.GetString(result);
        return data;
    }
 
    protected static string UrlEncode(string str)
    {
        return Uri.EscapeUriString(str);
    }
}

public class BitlyUrlShortener : UrlShortenerBase
{
    /// <summary>
    /// このソフトのログイン名
    /// </summary>
    public const string Login = "ログイン名";
    /// <summary>
    /// このソフトの API キー
    /// </summary>
    public const string ApiKey = "API キー";
    /// <summary>
    /// ユーザーのログイン名
    /// </summary>
    public string XLogin { get; set; }
    /// <summary>
    /// ユーザーの API キー
    /// </summary>
    public string XApiKey { get; set; }
    /// <summary>
    /// j.mp ドメインを使うか。true のとき http://j.mp/xxxxxx 、false のとき http://bit.ly/xxxxxx となる。
    /// </summary>
    public bool UseJmp { get; set; }
 
    /// <summary>
    /// bit.ly API のルート URL
    /// </summary>
    protected override string ApiUrl
    {
        get { return "http://api.bit.ly/"; }
    }

    /// <summary>
    /// 短縮 URL を取得
    /// </summary>
    /// <param name="longUrl"></param>
    /// <returns></returns>
    public override string Shorten(string longUrl)
    {
        const string command = "v3/shorten";
 
        var nvc = new NameValueCollection();
        nvc.Add("format", "xml");
        nvc.Add("login", Login);
        nvc.Add("apiKey", ApiKey);
        nvc.Add("longUrl", UrlShortenerBase.UrlEncode(longUrl));
        if (UseJmp){
            nvc.Add("domain", "j.mp");
        }
        if (!string.IsNullOrEmpty(XLogin) && !string.IsNullOrEmpty(XApiKey))
        {
            nvc.Add("x_login", XLogin);
            nvc.Add("x_apiKey", XApiKey);
        }
        var response = UrlShortenerBase.WebGet(this.GetRestUrl(command), nvc);
 
        var doc = new XmlDocument();
        doc.LoadXml(response);
        var statusCode = doc.SelectSingleNode("/response/status_code").InnerText;
        if (statusCode.Equals("200"))
        {
            return doc.SelectSingleNode("/response/data/url").InnerText;
        }
        else
        {
            return doc.SelectSingleNode("/response/status_txt").InnerText;
        }
    }

    /// <summary>
    /// 元の長い URL を取得
    /// </summary>
    /// <param name="shortUrl"></param>
    /// <returns></returns>
    public override string Expand(string shortUrl)
    {
        const string command = "v3/expand";
 
        var nvc = new NameValueCollection();
        nvc.Add("login", Login);
        nvc.Add("apiKey", ApiKey);
        nvc.Add("format", "xml");
        nvc.Add("shortUrl", UrlShortenerBase.UrlEncode(shortUrl));
        var response = UrlShortenerBase.WebGet(this.GetRestUrl(command), nvc);
 
        var doc = new XmlDocument();
        doc.LoadXml(response);
        var statusCode = doc.SelectSingleNode("/response/status_code").InnerText;
        if (statusCode.Equals("200"))
        {
            return doc.SelectSingleNode("/response/data/entry/long_url").InnerText;
        }
        else
        {
            return doc.SelectSingleNode("/response/status_txt").InnerText;
        }
    }
} // BitlyUrlShortener の終わりカッコ