Ensure templated parent control theme is applied

[jp2masa]

What does the pull request do?

Ensure templated parent control theme is applied.

What is the current behavior?

When templated parent control theme changes, styles are not applied, this affects Expander on Simple Theme (#10226).

What is the updated/expected behavior with this PR?

Styles are correctly applied.

How was the solution implemented (if it's not obvious)?

Override OnTemplatedParentControlThemeChanged on Layoutable and call InvalidateMeasure, like it's already being done for OnControlThemeChanged. Add missing !_templatedParentThemeApplied to ApplyStyling.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/Documentation with user documentation

Fixed issues

Fixes #10226

[jp2masa]

While fixing this I also found a possible bug, related to the following overrides:

Avalonia/src/Avalonia.Controls/Primitives/TemplatedControl.cs

Lines 399 to 429 in 4a4d713

	private protected override void OnControlThemeChanged()
	{
	base.OnControlThemeChanged();
	var count = VisualChildren.Count;
	for (var i = 0; i < count; ++i)
	{
	if (VisualChildren[i] is StyledElement child &&
	child.TemplatedParent == this)
	{
	child.OnTemplatedParentControlThemeChanged();
	}
	}
	}
	internal override void OnTemplatedParentControlThemeChanged()
	{
	base.OnTemplatedParentControlThemeChanged();
	var count = VisualChildren.Count;
	var templatedParent = TemplatedParent;
	for (var i = 0; i < count; ++i)
	{
	if (VisualChildren[i] is TemplatedControl child &&
	child.TemplatedParent == templatedParent)
	{
	child.OnTemplatedParentControlThemeChanged();
	}
	}
	}

It makes sense to override OnControlThemeChanged on TemplatedControl to call OnTemplatedParentControlThemeChanged on its visual children, i.e. the template.

However, for OnTemplatedParentControlThemeChanged what I understood is that it's propagating OnTemplatedParentControlThemeChanged to all children inside the template, but to be part of the template they don't have to be TemplatedControls, right? The minimum requirement is for them to be Visuals. Am I missing something?

[maxkatz6]

@jp2masa is it possible to add some tests, so it won't be regressed?

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0029785-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[grokys]

Sorry, this dropped off my radar - LGTM, thanks @jp2masa !

[grokys]

However, for OnTemplatedParentControlThemeChanged what I understood is that it's propagating OnTemplatedParentControlThemeChanged to all children inside the template, but to be part of the template they don't have to be TemplatedControls, right? The minimum requirement is for them to be Visuals. Am I missing something?

Yes, that's correct I think. I also notice we have no test coverage covering the for loop in OnTemplatedParentControlThemeChanged so we should fix that.

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0030363-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[jp2masa]

However, for OnTemplatedParentControlThemeChanged what I understood is that it's propagating OnTemplatedParentControlThemeChanged to all children inside the template, but to be part of the template they don't have to be TemplatedControls, right? The minimum requirement is for them to be Visuals. Am I missing something?

Yes, that's correct I think. I also notice we have no test coverage covering the for loop in OnTemplatedParentControlThemeChanged so we should fix that.

Opened #10471 with a test and fix.