Get all values of a NameValueCollection to a string

var col = new NameValueCollection() { { "a", "b" }, { "1", "2" } }; // collection initializer

var values = col.Cast<string>().Select(e => col[e]); // b, 2

var str = String.Join(",", values );  // "b,2"

Also you can create an extension method:

public static string Join(this NameValueCollection collection, Func<string,string> selector, string separator)
{
    return String.Join(separator, collection.Cast<string>().Select(e => selector(e)));
}

Usage:

var s = c.Join(e => String.Format("\"{0}\"", c[e]), ",");

Also you can easily convert NameValueCollection to more handy Dictionary<string,string> so:

public static IDictionary<string,string> ToDictionary(this NameValueCollection col)
{
    return col.AllKeys.ToDictionary(x => x, x => col[x]);
}

Gives:

var d = c.ToDictionary();

As I found using Reflector, NameValueCollection.AllKeys internally performs a loop to gather all te keys, so it seems that c.Cast<string>() is more preferable.