c# - Windows Phone 8 show MessageBox when app closing (deactivated) -

i trying show user messagebox before app closed (or deactivated). added both events:

if (appsettings.shouldshowalerttransfer)                 {                     messagebox.show("...");                 } 

but messagebox not shown. adding because adding background transfers , must inform user created background trasnfers. know can add code onkeybackpressed in every page. it's working key , not middle button. , wouldn't nice have same code copied in every page.

so possible show messagebox in app.xaml.cs? how can that? if it's not how can show messagebox when user pressed middle button?

i intrigued question opened solution , attempted every single override available , every single page event. tried of methods in app.xaml.cs.

i can unequivocally say, based on msdn documentation , own personal testing there no way detect home button press or search button press. furthermore there no way display message box temporarily stop 1 of these actions.

this testing done on windows phone 8 wvga 512mb emulator in visual studio 2013 ultimate.