Text Editor - preserve style of previous text

See more:

C#

Windows

XAML

Win8

RichTextBox

Hi All

I am working on text editor for windows 8 app so i am using RichEditBox control. i am just using Bold, Italic and underline for style formatting. it work fine with selected text but the issue is when there is no text is selected if i click any B/I/U button the style of character in editor must change accordingly but not whole text in editor only next typed characters must get those style. for example you can refer MS Word. Please help me how to achieve.

Thanks in advance