Confirming Navigaton

A ViewModel can determine whether or not it can perform a navigation operation. When a ViewModel implements the IConfirmNavigation or the IConfirmNavigationAsync interface, the navigation process looks to see what the result of this method is. If true, a navigation process can be invoked, meaning a call to NavigationService.NavigateAsync("target") can be made. If false, the ViewModel cannot invoke the navigation process.

IConfirmNavigation

public class ContactPageViewModel : IConfirmNavigation 
{
  public bool CanNavigate(NavigationParameters parameters)
  {
    return true;
  }
}

IConfirmNavigationAsync

public class ContactPageViewModel : IConfirmNavigationAsync
{
  public Task<bool> CanNavigateAsync(INavigationParameters parameters)
  {
    return _pageDialogService.DisplayAlertAsync("Save", "Would you like to save?", "Save", "Cancel");
  }
}