[Win32] Fixes improper IME composition ignorance

[gehongyan]

What does the pull request do?

When focusing on an input element, it goes through a series of calls, ultimately reaching the Imm32InputMethod.Reset method via TextInputMethodManager.TryFindAndApplyClient. Within this method, a task submitted to the UI thread sets _ignoreComposition to true, ignoring the first typed character or the first selected candidate word to be submitted at the end of string composition.

This incorrect behavior was introduced in #11723, resolving issue #11292. However, the current solution introduces another problem, as described in #14663.

What is the current behavior?

When the focus changes, _ignoreComposition is set to true as described above, and is reset to false when handling the next composition message.

Avalonia/src/Windows/Avalonia.Win32/Input/Imm32InputMethod.cs

Line 130 in a33b39e

_ignoreComposition = true;

Avalonia/src/Windows/Avalonia.Win32/Input/Imm32InputMethod.cs

Lines 352 to 357 in a33b39e

	if (_ignoreComposition)
	{
	_ignoreComposition = false;
	return;
	}

However, if there is no unfinished composition when switching focus, _ignoreComposition remains true, causing the next composition message to be unexpectedly ignored.

What is the updated/expected behavior with this PR?

_ignoreComposition should not be kept true when no uncompleted string compositions exist, so that the next string composition message can be handled well.

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

The current merge request introduces a condition before setting _ignoreComposition to true. It only sets _ignoreComposition to true when there is ongoing input method string composition, namely IsComposing is true. This prevents _ignoreComposition from being inadvertently retained, addressing issue #14663.

Checklist

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

Breaking changes

None.

Obsoletions / Deprecations

None.

Fixed issues

Fixes #14663
Fixes #13881

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0045147-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[Gillibald]

Thank you for your detailed PR

This is very much appreciated!