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?

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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...