Listening to caret update WPF TextBox

I remembered that I completely solved this problem, so I looked at my old code and found it. All the changes in caret position will be caught if you override the virtual method TextBox.OnSelectionChanged. You can also handle the event SelectionChanged, of course. I prefer to subclass the control and advice you to do so, as you are implemented a bit more advanced features. For a bonus, I'll show you how to calculate caret position in terms of line/column. Assuming you subclass the text box, it will look like this:

partial class MyTextBox : TextBox {

     void InquireCaretPosition(out Position line, out Position column) {
         line = 0; column = 0;
         int caret = this.CaretIndex;
         int iLine = this.GetLineIndexFromCharacterIndex(caret);
         if (iLine < 0) iLine = 0;
         line = iLine;
         int firstChar = this.GetCharacterIndexFromLineIndex(iLine);
         if (firstChar  0) firstChar = 0;
         column = caret - firstChar;
     }

     protected override void OnSelectionChanged(RoutedEventArgs e) { //for example
         base.OnSelectionChanged(e);
         ShowPosition();
     }

     void ShowPosition() {
        int line, column;
        InquireCaretPosition(out line, out column);
        //show line and column in status line or something like that    
     }

     //...

}

Don't forget to show position on some other events, such as when your text box is shown, etc.

Good luck,

—SA