Question

I am programming WP7 application adhering the MVVM pattern.

I have ViewModelLocator which ensures that each instance of ViewModel is only one. These ViewModels are created when application is launched. ViewModels communicating with each other using messages. I use messages for navigatig to next Page (For this I am using NavigationService.Navigate(), which is Raised from MainPage CodeBehind – it is the only functionality that is in CodeBehind ). View and ViewModels are connected together by setting the DataContext in the Page to ViewModelLocator.

Everythig works at first sight.

But during each navigation, there is created new Page instance, which is connected to the ViewModel from ViewModelLocator(which is designed for it). The result is that: when a user often switches between pages, there are multiple instances of a page connected to one ViewModel. Of course, there is visible only one page at one point.

Very simple solution could be setting NavigationCache, but it is readonly in WP7.

I am looking for solution of unwanted behavior.

Answer 1

Every time you Navigate somewhere a new instance is created for that page.
You could avoid this by using NavigationService.GoBack(); where ever you can.

You should also unregister from every event when navigating away from the page, so that way the garbage collector can clear out that page.

I hope this helps.