Static private data member not initialized in static class?

Question

Given the C# code below, I expected the private data member _userDataStorage to be initialized immediately. Instead I find that it is not being initialized at all. I put a breakpoint on the initialization statement and it is never hit. This means the DB static property always returns NULL. Do static classes work differently than non-static classes?

public static class UserDataStorageWrapper
{
    private static UserDataStorage _userDataStorage = new UserDataStorage();

    public static UserDataStorage DB
    { 
        get
        {
            return _userDataStorage;
        }
    }
}

I will change the code to check for NULL and initialize _userDataStorage myself for now. But I want be sure about my expectations here.

Answer 1

Try adding a static constructor and initialize the variable inside.

public static class UserDataStorageWrapper
{
    public static UserDataStorageWrapper()
    {
        _userDataStorage = new UserDataStorage();
    }

    private static UserDataStorage _userDataStorage;

    public static UserDataStorage DB
    { 
        get
        {
            return _userDataStorage;
        }
    }
}

"If a static constructor exists in the class, execution of the static field initializers occurs immediately prior to executing that static constructor" source

Answer 2

Since it is a static initializer it will be initialized "at an implementation-dependent time prior to the first use of a static field of that class". Source

So your breakpoint might not get hit unless you use that field (or another static field in that class).

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For completeness I can add that if there is a static constructor, the static field initializers will be executed before the static constructor.