protected override void OnNavigatedTo(NavigationEventArgs e)
{
base.OnNavigatedTo(e);
AppViewModel = e?.Parameter as AppLevelModel;
AppViewModel.MessageToDisplay += AppViewModel_MessageToDisplay;
AppViewModel.NavigateBack -= NavigateBack;
AppViewModel.NavigateBack += NavigateBack;
AppViewModel.NavigateTo += (page, viewModel, command, reentry) =>
{
if (reentry || viewModel != AppViewModel?.ChildViewmodel)
{
viewModel.OnNavigatingTo();
MainPaneFrame.Navigate(page, viewModel);
AppViewModel.VisitedPages.Push(viewModel);
AppViewModel.ChildViewmodel = viewModel;
AppViewModel.CanGoBack = !viewModel.IsInitialAppPage;
ContentSplitView.IsPaneOpen = false;
command?.Execute();
}
};
}
/// <summary>
/// Try to navigate Back
/// </summary>
/// <returns>True if operation successful</returns>
private async Task <bool> TryNavagatingBack()
{
if (MainPaneFrame.CanGoBack && AppViewModel.VisitedPages.Count > 1)
{
// Get previous viewmodel
var prevPage = AppViewModel.VisitedPages.Pop();
// Perform any cleanup before navigating away.
if (await prevPage.OnNavigatingFrom())
{
// We can navigate back. Perform cleanup and navigate back
if (AppViewModel.ChildViewmodel != null)
{
AppViewModel.ChildViewmodel = AppViewModel.VisitedPages.Peek();
// Make sure any submenus are not unnecessarily selected
if (AppViewModel.ChildViewmodel.ResetMainMenuIndexOnNavigation)
{
AppViewModel.ChildViewmodel.MainMenuIndex = -1;
}
if (AppViewModel.ChildViewmodel.ResetSubMenuIndexOnNavigation)
{
AppViewModel.ChildViewmodel.SubMenuIndex = -1;
}
if (AppViewModel.ChildViewmodel.ResetBottomMenuIndexOnNavigation)
{
AppViewModel.ChildViewmodel.BottomMenuIndex = -1;
}
}
AppViewModel.CanGoBack = !AppViewModel.ChildViewmodel.IsInitialAppPage;
// Go to previous page
MainPaneFrame.GoBack();
return(true);
}
else
{
// Navigation cancelled. Restore navigation stack.
AppViewModel.VisitedPages.Push(prevPage);
return(false);
}
}
else
{
AppViewModel.CanGoBack = false;
return(false);
}
}
private async void NavigationHelper(MenuItem <AppLevelModel> item, int currentIndex)
{
if (item.UseBackButton)
{
await TryNavagatingBack();
}
else
{
if (item.Reentry || item.ViewModel != AppViewModel?.ChildViewmodel)
{
bool canNavigate;
if (AppViewModel.VisitedPages.Count == 0)
{
// No page to navigate away from
canNavigate = true;
}
else
{
// Allow page to perform any cleanup if necessary.
var currentPage = AppViewModel.VisitedPages.Peek();
canNavigate = await currentPage.OnNavigatingFrom();
}
if (canNavigate)
{
item.BeforeNavigatingCommand?.Execute();
MainPaneFrame.Navigate(item.Page, item.ViewModel);
AppViewModel.VisitedPages.Push(item.ViewModel);
AppViewModel.ChildViewmodel = item.ViewModel;
AppViewModel.CanGoBack = !item.ViewModel.IsInitialAppPage;
item.AfterNavigatingCommand?.Execute();
}
}
}
}