Win8 store Application, do some check in the OnNavigatedFrom Method - windows-store-apps

Question

I wanted to do some check, when I click the NavigateButton(Back) to home page.
1.Display the MessageDialog show update the content "yes" or "not"
2.If click yes, update current page.
If click No, do nothing
3.navigate to homepage.
I use below code, but currently it will back to the home page first, and then pop up the message dialog.
how can I let the action that navigate to homepage happened after I clicked the message dialog
protected async override void OnNavigatedFrom(NavigationEventArgs e)
{
MessageDialog md = new MessageDialog("Do you want to save");
md.Commands.Add(new UICommand("Yes", (UICommandInvokedHandler) =>
{
Application.Current.Exit();
//this.UpdateClick();
}));
md.Commands.Add(new UICommand("No"));
var task = md.ShowAsync().AsTask();
await task;
}

Answer 1

OnNavigateFrom is not cancel-able, and happens after the navigation has already occurred.
Rather than having the code, why don't you re-wire the back button to a click handler which pops up the message box? Then when the user clicks a button, you perform the appropriate navigation.
private async void OnBackButtonClick(object sender, RoutedEventArgs routedEventArgs)
{
MessageDialog md = new MessageDialog("Do you want to save");
md.Commands.Add(new UICommand("Yes", uiCommandInvokedHandler =>
{
// Refresh logic
}));
md.Commands.Add(new UICommand("No", uiCommandInvokedHandler =>
{
var rootFrame = (Frame)Window.Current.Content;
rootFrame.Navigate(typeof(MainPage));
}));
await md.ShowAsync();
}