Keep routed window-close triggers active through closure

[wieslawsoltes]

Summary

Allows a RoutedEventTriggerBehavior attached directly to a window to receive Window.WindowClosedEvent and execute actions whose bindings come from the window data context.

Root cause

Window shutdown crosses three distinct lifecycle points:

1. the window leaves the visual/logical tree;
2. WindowClosedEvent is raised;
3. behavior resources can be released.

The previous implementation treated step 1 as the end of the behavior lifetime:

• RoutedEventTriggerBehavior.OnDetachedFromVisualTree removed the routed handler;
• getter-created behavior collections detached immediately;
• StyledElementBehavior removed the behavior/action logical parent, clearing the bound InvokeCommandAction.Command.

As a result, simply retaining the routed handler was not enough: the event could be observed, but the command binding had already been torn down.

Changes

• For a trigger attached directly to a TopLevel whose resolved event source is also a TopLevel:
  • retain the routed handler across visual detachment;
  • execute a routed event that arrives during that closing interval;
  • remove the handler after that post-detach event or on actual behavior detachment.
• Keep ordinary control triggers tied to their existing visual-tree lifetime.
• Preserve a top-level behavior's logical parent and action bindings through the closing event.
• Defer getter-created top-level collection detachment by one dispatcher turn:
  • this lets the synchronous closed event complete first;
  • the collection is then detached if the same top-level/collection has not reattached or been replaced.
• Document the supported window-close pattern.

Tests

Exact issue regression

A compiled-XAML headless window uses:

<RoutedEventTriggerBehavior RoutedEvent="{x:Static Window.WindowClosedEvent}">
  <InvokeCommandAction Command="{Binding CloseCommand}" />
</RoutedEventTriggerBehavior>

The test verifies:

• the routed action runs exactly once;
• the compiled bound command runs exactly once;
• the behavior is detached after the closing event;
• raising the event again cannot execute either action.

Lifecycle safeguards

Additional coverage verifies:

• an ordinary control trigger unsubscribes when its control leaves the visual tree;
• a top-level styled behavior retains its logical parent during the closing interval;
• deferred detachment subsequently clears both the associated object and logical parent.

Validation:

• dotnet test tests/Xaml.Behaviors.Interactivity.UnitTests/Xaml.Behaviors.Interactivity.UnitTests.csproj --no-restore
  • 94 passed, 0 failed
• dotnet test tests/Xaml.Behaviors.Interactions.UnitTests/Xaml.Behaviors.Interactions.UnitTests.csproj --no-restore
  • 91 passed, 2 existing drag tests skipped, 0 failed

Closes #337

[chatgpt-codex-connector]

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