[Fix] NavigationView: Improve load & Fix ListView Size Initialization Issue

[Jack251970]

Improve NavigationView load

Port from microsoft-ui-xaml. Update visual state on OnLoaded event to improve display effect.

Fix ListView Size Initialization Issue

Set NavigationView.IsPaneOpen default to false to fix ListView size initialization issue if NavigationView default DisplayMode is Compact.

Test

Original:

After:

[Copilot]

Pull Request Overview

This PR addresses a popup root exception that occurs when NavigationView is placed within a popup and makes changes to the IsPaneOpen property's default value. The main fix defers SplitView DisplayMode updates that occur during OnApplyTemplate to the OnLoaded event to prevent exceptions when NavigationView is in the popup root.

• Wraps the OnApplyTemplate logic in a try-finally block with a flag to track when the template is being applied
• Defers SplitView DisplayMode updates during OnApplyTemplate to the OnLoaded event to avoid popup root exceptions
• Removes the default value (true) from the IsPaneOpen dependency property, making it default to false

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
NavigationView.cs	Adds try-finally block around OnApplyTemplate, introduces flags to track template application state and defer SplitView DisplayMode updates to OnLoaded event
NavigationView.properties.cs	Removes explicit default value (true) from IsPaneOpenProperty metadata

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Missing space between backtick and 'to' - should be 'OnApplyTemplate to'.

Suggested change

	// Due to this, we want to defer updating this property for all calls coming from `OnApplyTemplate`to the OnLoaded function.
	// Due to this, we want to defer updating this property for all calls coming from `OnApplyTemplate` to the OnLoaded function.

[Copilot]

Removing the default value (true) from IsPaneOpenProperty changes the default behavior from pane open to pane closed. This is a breaking change that affects any existing code relying on the pane being open by default. Consider adding the default value back with 'new PropertyMetadata(true, OnIsPaneOpenPropertyChanged)' or document this as a breaking change.

Suggested change

	new PropertyMetadata(OnIsPaneOpenPropertyChanged));
	new PropertyMetadata(true, OnIsPaneOpenPropertyChanged));