I have this class, that implements the singleton pattern, and a subclass.

public class Base
{
    public static Base Instance;
    static Base()
    {
      System.Type myType = MethodInfo.GetCurrentMethod().DeclaringType;
      Instance = (Base)Activator.CreateInstance(myType);
    }

    public void ID()
    {
      MessageBox.Show("I am " + this.GetType().Name);
    }

}

public class Sub : Base
{
}

When I call Base.Instance.ID(), I get "I am Base", which is what I want.
When I call Sub.Instance.ID(), I also get "I am Base". This makes sense,
since MethodInfo.GetCurrentMethod().DeclaringType SHOULD return Base, since that's where it's declared.

The question is - is there any way to tell, when Base's static constructor is called - which object I am, in fact, instantiating? Or, since it's static, there really isn't any Sub object to get info from?

4 Comments

• Jim Arnold said Tuesday, September 14, 2004 4:23:00 PM

  You could walk back up the stack to get the calling method (the static constructor is 'called' implicitly by the first method accessed on a class). Of course, if the first thing accessed on that class is a field, then the caller will be the method which is accessing that field, which doesn't help you much. I haven't really thought it through, but it might be what you want:
  
  static Base()
  {
  StackFrame lastFrame = new StackFrame(1);
  MethodBase caller = lastFrame.GetMethod();
  Console.WriteLine(caller.DeclaringType.Name);
  }
  
  Jim

• Omer van Kloeten said Tuesday, September 14, 2004 6:04:00 PM

  Avner,
  
  To get the type use:
  
  Type myType = new System.Diagnostics.StackTrace().GetFrame(2).GetMethod().DeclaringType;
  
  0 is the cctor for the base.
  1 is the implicit ctor for the base.
  2 is the implicit ctor for the derived.
  
  Jim,
  
  You've missed one of the implicit ctors - the stack frame's constructor should skip 2 frames.
  However, it works the same way. :)

• Avner Kashtan said Tuesday, September 14, 2004 6:08:00 PM

  I seem to remember that walking through StackFrames is very slow. True?

• Jim Arnold said Tuesday, September 14, 2004 7:20:00 PM

  Omer,
  
  "1 is the implicit ctor for the base."
  
  Only if you're calling an instance method, surely? It's a bit of a minefield though :-)
  
  "I seem to remember that walking through StackFrames is very slow"
  
  Well, compared to what? And if you're calling it from a static constructor, it's only going to run once anyway.
  
  Jim