The type initializer for '' threw an exception

.net, c#, exception

Solution

Judging by your stack trace, I think you've missed out the guilty code. For example, maybe it actually looks like this:

public class CountEnum
{
   public static readonly CountEnum DEFAULT = new CountEnum();
   private static readonly List<CountEnum> AllInstances = new List<CountEnum>();

   private CountEnum()
   {
       AllInstances.Add(this);
   }
}

That would behave the way the stack trace shows, with the `CountEnum` constructor throwing a `NullReferenceException`. However, we can't tell for sure as you haven't included the body of the `CountEnum` constructor (or indeed posted valid code for `CountEnum` at all).

Fundamentally though, this is the bit of the stack trace you should be looking at:

InnerException: System.NullReferenceException
     Message=Object reference not set to an instance of an object.
     Source=CP.DataObject
     StackTrace:
          at CP.Types.CountEnum..ctor(String code, String name) in C:\...\CountEnum.cs:line 23
          at CP.Types.CountEnum..cctor() in C:\...\CountEnum.cs:line 8

You should be looking at line 23 of `CountEnum.cs` - that's what's throwing the exception.

EDIT: Okay, now we can see the code in question, it's very similar to my guess. Look at this code:

public static readonly CountEnum CANADA = new CountEnum("CA", "Canada");
public static readonly CountEnum DEFAULT = new CountEnum();
private static readonly EnumDataTypeList OPTIONS = new EnumDataTypeList();

These variables will be initialized in the order you've specified - so the call to `CountEnum("CA", "Canada")` will execute before `OPTIONS` has a non-null value... and when you try to add it to `OPTIONS`, you'll get an exception in a perfectly normal way.

You can fix this just by moving the declaration of `OPTIONS` to the top:

private static readonly EnumDataTypeList OPTIONS = new EnumDataTypeList();
public static readonly CountEnum CANADA = new CountEnum("CA", "Canada");
public static readonly CountEnum DEFAULT = new CountEnum();

That's guaranteed to work, but it's a fairly brittle design. I have used designs like this in the past, but you can get into fiddly messes when you require a particular initialization order.

Problem

Original source