Fix WPF View deactivation

[nathanpovo]

What kind of change does this PR introduce?

Bug fix.

What is the current behavior?

When a WPF application is shutdown, the Unloaded event is not fired and, as a result, the View is not deactivated by ReactiveUI; as explained in the issue #2490.

What is the new behavior?

The ActivationForViewFetcher will observe the Closing event (if the View is a Window) to determine if the View should be deactivated.

What might this PR break?

Nothing.

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

[dnfadmin]

All CLA requirements met.

[glennawatson]

Thanks, I'll see if I can merge this in tonight for you.

Just noticed the CI server had a software change so need to adapt.

Thanks for the contribution.

[nathanpovo]

I have been doing some additional tests with the updated library and just adding an observable base on the Closed event is not enough.

When a ReactiveWindow is closed, the Closed event is fired and the ActivationForViewFetcher informs any observers that the view has been deactivated, as expected.

However, any ReactiveUserControls in that ReactiveWindow (or even a normal Window) will not be deactivated; a ReactiveUserControl is not derived from a Window so it does not have the Closed event, and the Unloaded event is not fired when an application is closing.

[worldbeater]

Yeah relying on the ShutdownStarted event should work as per https://stackoverflow.com/a/14480184/11351183

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.