Declare a dictionary inside a static class

Question

How to declare a static dictionary object inside a static class? I tried

public static class ErrorCode {     public const IDictionary<string, string> ErrorCodeDic = new Dictionary<string, string>()     {         { "1", "User name or password problem" }          }; } 

But the compiler complains that "A const field of a reference type other than string can only be initialized with null".

Answer 1

If you want to declare the dictionary once and never change it then declare it as readonly:

private static readonly Dictionary<string, string> ErrorCodes     = new Dictionary<string, string> {     { "1", "Error One" },     { "2", "Error Two" } }; 

If you want to dictionary items to be readonly (not just the reference but also the items in the collection) then you will have to create a readonly dictionary class that implements IDictionary.

Check out ReadOnlyCollection for reference.

BTW const can only be used when declaring scalar values inline.