windows phone 8 - How can you prevent a ContentDialog from closing on button press in WP8 -

in windows phone 8 (or 8.1), there way prevent contentdialog closing when primary button pressed under conditions? example, have boolean done. when click primary button, want contentdialog close if (done == true). possible?

xaml:

<contentdialog     ...     closing="contentdialog_closing"> 

c#:

private async void contentdialog_closing(contentdialog sender, contentdialogclosingeventargs args) {     if (!canclose)         args.cancel = true; }