Replace item in querystring

Question

I have a URL that also might have a query string part, the query string might be empty or have multiple items.

I want to replace one of the items in the query string

Answer 1

I used the following code to append/replace the value of a parameter in the current request URL:

    public static string CurrentUrlWithParam(this UrlHelper helper, string paramName, string paramValue)
    {
        var url = helper.RequestContext.HttpContext.Request.Url;
        var sb = new StringBuilder();

        sb.AppendFormat("{0}://{1}{2}{3}",
                        url.Scheme,
                        url.Host,
                        url.IsDefaultPort ? "" : ":" + url.Port,
                        url.LocalPath);

        var isFirst = true;

        if (!String.IsNullOrWhiteSpace(url.Query))
        {
            var queryStrings = url.Query.Split(new[] { '?', ';' });
            foreach (var queryString in queryStrings)
            {
                if (!String.IsNullOrWhiteSpace(queryString) && !queryString.StartsWith(paramName + "="))
                {
                    sb.AppendFormat("{0}{1}", isFirst ? "?" : ";", queryString);
                    isFirst = false;
                }
            }
        }

        sb.AppendFormat("{0}{1}={2}", isFirst ? "?" : ";", paramName, paramValue);

        return sb.ToString();
    }

Maybe this helps others when finding this topic.

Update:

Just saw the hint about UriBuilder and did a second version using UriBuilder, StringBuilder and Linq:

    public static string CurrentUrlWithParam(this UrlHelper helper, string paramName, string paramValue)
    {
        var url = helper.RequestContext.HttpContext.Request.Url;
        var ub = new UriBuilder(url.Scheme, url.Host, url.Port, url.LocalPath);

        // Query string
        var sb = new StringBuilder();
        var isFirst = true;
        if (!String.IsNullOrWhiteSpace(url.Query))
        {
            var queryStrings = url.Query.Split(new[] { '?', ';' });
            foreach (var queryString in queryStrings.Where(queryString => !String.IsNullOrWhiteSpace(queryString) && !queryString.StartsWith(paramName + "=")))
            {
                sb.AppendFormat("{0}{1}", isFirst ? "" : ";", queryString);
                isFirst = false;
            }
        }
        sb.AppendFormat("{0}{1}={2}", isFirst ? "" : ";", paramName, paramValue);
        ub.Query = sb.ToString();

        return ub.ToString();
    }