How to update ViewModel while navigating using MVVM

Question

When navigating the back button on the phone, how can I update the ViewModel?

I use the back button on the phone, but I find it to be the same as calling NavigationService.GoBack (), which moves to the previous page on the stack, but the constructor is not called in my view or ViewModel.

Answer 1

You can connect the base class of the page to the OnNavigatingTo event and call the method on your ViewModel. I don't have VS with me, but the pseudocode will be:

in MyBasePAge: Page

public void OnNavigatingTo(object sender, eventargs e)
{
   var vm = this.DataContext as BaseViewModel;
   if(vm != null)
   {
      vm.Initialize();
   }
 }

you can do the same before leaving the page:

public void OnNavigatingFrom(object sender, eventargs e)
{
   var vm = this.DataContext as BaseViewModel;
   if(vm != null)
   {
      vm.Save();
   }
 }