How to display multiple text in richtextbox during runtime before the event is ended

I m making an wpf window application using C# language.I have an button click event in which there are 3 function are called and executed one after the another.
After completion of each function, i want to update the richtextbox in ma UI with text and output of that function dynamically.
but the richtextbox are updated after the completion of the button click event,But i wan to update before the click event is closed i.e as soon as any function is executed, it update the richtextbox with its output.


Pls help to sort out.