以NameValueCollection 修改URL中的查询参数

private string UpdateQueryString() {

    string urlOld = "http://www.cnblogs.com/freeliver54?KeyB=ValueB&KeyD=ValueD&KeyC=ValueC";
            //System.Web.HttpUtility.UrlDecode(returnUrl, Encoding.Unicode);
    string urlNew = "";

    if (urlOld.Contains("?"))
    {
        string[] separateURL = urlOld.Split(‘?‘);

        System.Collections.Specialized.NameValueCollection queryString = System.Web.HttpUtility.ParseQueryString(separateURL[1]);

        queryString.Remove("KeyD");
        queryString.Add("KeyA", "ValueA");
        queryString["KeyB"] = "ValueB2";

        urlNew = separateURL[0] + "?" + queryString.ToString();
    }
    else
    {
        urlNew = urlOld + "?KeyA=ValueA" ;
    }

    return urlNew;
}