c# - Cursor position inside a RichTextBox in WPF -

i developing small wpf application, has multiple tabs in it. have status bar in bottom; requirement show linenumber , column of cursor. when user changes cursor position, linenumber , column has updated automatically. here code add richtextbox; code calculates linenumber , column in keydown event handler, event never gets called. event should handle cursor linenumber , column?

private void addtabitem(string filepath, mode filemode) {     if (filemode == mode.openfile)     {         if (file.exists(filepath))         {             richtextbox mcrtb = new richtextbox();             mcrtb.keydown += new keyeventhandler(linenumber); //rest of code goes here         }     } } mcrtb.keydown += new keyeventhandler(linenumber);  private void linenumber(object sender, keyeventargs e) {               textpointer tp1 = rtblist[editortabcontrol.selectedindex].selection.start.getlinestartposition(0);     textpointer tp2 = rtblist[editortabcontrol.selectedindex].selection.start;      int column = tp1.getoffsettoposition(tp2);      int somebignumber = int.maxvalue;     int linemoved, currentlinenumber;     rtblist[editortabcontrol.selectedindex].selection.start.getlinestartposition(-somebignumber, out linemoved);     currentlinenumber = -linemoved;     string linecolumnlabel;      //linecolumnlabel.content = "line: " + currentlinenumber.tostring() + " column: " + column.tostring();     linecolumnlabel = "line: " + currentlinenumber.tostring() + " column: " + column.tostring();         } 

there standard example task @ msdn (http://msdn.microsoft.com/en-us/library/system.windows.controls.richtextbox.caretposition%28v=vs.110%29.aspx). please note, in context 'cursor' called 'caret'. sample msdn follows:

// create new flowdocument, , add 3 paragraphs. flowdocument flowdoc = new flowdocument(); flowdoc.blocks.add(new paragraph(new run("paragraph 1")));  flowdoc.blocks.add(new paragraph(new run("paragraph 2")));  flowdoc.blocks.add(new paragraph(new run("paragraph 3"))); // set flowdocument content new richtextbox. richtextbox rtb = new richtextbox(flowdoc);  // current caret position. textpointer caretpos = rtb.caretposition;  // set textpointer end of current document. caretpos = caretpos.documentend;  // specify new caret position @ end of current document. rtb.caretposition = caretpos;