Find The Value Of The Key Pressed Down In A WPF Project?

I am working on a WPF project in Visual Basic. In some textboxes I want to limit what the user should be able to type. The sub roughly looks like this:

Private Sub Intervall_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Input.KeyEventArgs) Handles Intervall.KeyDown
'Determine whether the keystroke is a digit from the digit keys on the top of the keyboard.

[Code]....

If the I type backspace or delete, keydown doesn't react, so these particular cases I've handled in KeyUp.

There are two problems with this code: The test If e.Key < Key.D0 only checks whether the user has pressed the key that contains 0 at the top of the keyboard. It is also possible to enter some other signs if the user presses shift, and this test doesn't discover whether the user presses shift. I therefore need to extract the actual character that the user entered, not only which key he or she entered, and check if this character is a legal one. This is easy in a Windows.Forms project; there I can use e.Keyvalue, but in my WPF project I don't get that alternative when I enter a dot after "e".

It's necessary to solve this problem in order to do the next step: The user should also be allowed to enter colon, as this textbox describes a time that an action should be performed. If I could check the content of the key pressed, this would be easy. The problem is that the test If e.Key = Key.OemPeriod returns true whether the user pressed shift or not, i.e. whether the user entered a period or a colon, which are on the same key on my keyboard, I don't know how it is on other standards of keyboards.

I have tried hard to find a solution for this on Google, [URL] and MSDN, but I haven't managed to find any articles or topics about this particular problem. Does anyone know how to do this in a WPF project?