Create a URL query string from a NameValueCollection in C#

queryString.cs

var nvc = new NameValueCollection
    {
        { "key1", "value1" },
        { "key2", "value2" },
        { "key3", "" }
    };


var builder = new UriBuilder("http://www.example.com");

// Create query string with all values
builder.Query = string.Join("&", nvc.AllKeys.Select(key => string.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(nvc[key]))));

// Omit empty values
builder.Query = string.Join("&", nvc.AllKeys.Where(key => !string.IsNullOrWhiteSpace(nvc[key])).Select(key => string.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(nvc[key]))));

@theShiva, since .NET 4.5 you can use System.Net.WebUtility, which is in the System.dll assembly.

You can use this class in portable library or WinRT/Windows Phone

I know this is old but I thought I would update with a version that takes multiple querystring values into account to be compliant with the RFC:

uri.Query = string.Join("&",
                    nvc.AllKeys.Where(key => !string.IsNullOrWhiteSpace(nvc[key]))
                        .Select(
                            key => string.Join("&", nvc.GetValues(key).Select(val => string.Format("{0}={1}", HttpUtility.UrlEncode(key), HttpUtility.UrlEncode(val))))));