How to cancel WPF app closing from Page?

Question

I'm using a WPF NavigationWindow and some Pages and would like to be able to know when the application is closing from a Page.
How can this be done without actively notifying the page from the NavigationWindow_Closing event handler?

I'm aware of the technique here, but unfortunately NavigationService_Navigating isn't called when the application is closed.

Answer 1

One way to do this is have the pages involved support an interface such as:

public interface ICanClose
{
     bool CanClose();
}

Implement this interface at the page level:

public partial class Page1 : Page,  ICanClose
{
    public Page1()
    {
        InitializeComponent();
    }

    public bool CanClose()
    {
        return false;
    }
}

In the navigation window, check to see if the child is of ICanClose:

private void NavigationWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
    ICanClose canClose = this.Content as ICanClose;

    if (canClose != null && !canClose.CanClose())
        e.Cancel = true;
}