protected async override void OnNavigatingFrom()

in ContosoApp/Views/OrderDetailPage.xaml.cs [96:135]
35 lines of code
6 McCabe index (conditional complexity)

        protected async override void OnNavigatingFrom(NavigatingCancelEventArgs e)
        {
            if (ViewModel.IsModified)
            {
                var saveDialog = new SaveChangesDialog()
                {
                    Title = $"Save changes to Invoice # {ViewModel.InvoiceNumber.ToString()}?",
                    Content = $"Invoice # {ViewModel.InvoiceNumber.ToString()} " + 
                        "has unsaved changes that will be lost. Do you want to save your changes?"
                };

                await saveDialog.ShowAsync();
                SaveChangesDialogResult result = saveDialog.Result;

                switch (result)
                {
                    case SaveChangesDialogResult.Save:
                        await ViewModel.SaveOrderAsync();
                        break;
                    case SaveChangesDialogResult.DontSave:
                        break;
                    case SaveChangesDialogResult.Cancel:
                        if (e.NavigationMode == NavigationMode.Back)
                        {
                            Frame.GoForward();
                        }
                        else
                        {
                            Frame.GoBack();
                        }
                        e.Cancel = true;

                        // This flag gets cleared on navigation, so restore it. 
                        ViewModel.IsModified = true; 
                        break;
                }
            }

            base.OnNavigatingFrom(e);
        }