Why has the selector class an internal Constructor?

I tried to derive from the Selector class cause I need a similar functionality as the ListBox but it is no ListBox. I had a look at the signature of the Selector class and it is (http://msdn.microsoft.com/en-us/library/system.windows.controls.primitives.selector(v=vs.95).aspx)

public abstract cla开发者_StackOverflowss Selector : ItemsControl, 
ISupportInitialize

But the problem is that the constructor is internal. So it is not possible to derive from this class outside the assembly (ListBox and ComboBox are in this assembly).

I now derived from the ListBox to achieve my goal, but my question is:

Why has the selector class an internal Constructor?

Because the Selector class is abstract. You can't create instances of abstract classes, and the easiest way to make sure you can't even do that by mistake (in a regular way) is to not make a constructor available.

I don't see an entry for the constructor on the MSDN, but my bet is that it's probably a protected constructor, not an internal one.

But from what I can see, nothing stops you from deriving from Selector, and create your custom implementation.

Edit: Reflector shows the constructor to be internal indeed, so no deriving...