Use TryGetValue to get a value out
using System; using System.Collections.Generic; public class Example { public static void Main() { Dictionary<string, string> openWith = new Dictionary<string, string>(); openWith.Add("A", "a"); openWith.Add("B", "b"); openWith.Add("C", "c"); string value = ""; if (openWith.TryGetValue("AAAA", out value)) { Console.WriteLine(value); } else { Console.WriteLine(" is not found."); } } }