Comments by KEL3 (Top 6 by date)

I don't see a any "comboBox1.TextBox" either. That's the problem.
I guess I must do the trick inside the OnRender() override function... :(

You mean that you want countTrue to return 1 when data contains "W" else return 0 ?
If you write a normal for/foreach loop that does what you want perhaps I could give you the LINQ equivalent (if it exists).
Or give examples of input and output.

You say:
data={"W","H","X","V"} => return 3
data={"O","H","X","V"} => return 1
???

I don't understand what is countTrue() supposed to count...

Oups! My bad!
I CAN get the new value (I just do (e.OriginalSource as TextBox).Text). Forget what I said before.
The problem is how to set the event handler by code.
There doesn't seem to be any comboBox1.TextChanged.

Unfortunately not.
This is mostly a problem for ComboBoxes with the IsEditable property set to true.
There is a problem with ComboBox and when the event handler for TextChanged gets called (when you edit the text contents of it by typing inside it) you cannot see the new Text value (you see the value before modification).

This is a related discussion:
http://social.msdn.microsoft.com/Forums/en/wpf/thread/bf7de95a-b088-48e9-989f-d5f9e3a857da

Textboxbase.Textchanged solves a lot of problems, but I have problems accessing it by code...