Enable KeyDown events unconditionally on MacOS

[mikeyusc]

What does the pull request do?

KeyDown events were removed on MacOS from being fired for controls with an IME.

On Windows & Linux, every KeyStroke generates a KeyDown Event, then a TextInputEvent, followed by a KeyUp event. This also happens on MacOS, unless focus is on a control with an IME, where they KeyDown Events are being consumed, unless there is a modifier key present.

This removes the ability to use a Tunneling Event Handler to validate input, or check for a localized hotkey, and set the event as handled, so that the keystroke never makes it to the IME.

Currently, the following code for a TextBox (MyText) is never executed on MacOS, it functions correctly on Windows & Linux

MyText.AddHandler(KeyDownEvent, (sender, args) =>
{
    Debugger.Break();
}, RoutingStrategies.Tunnel);

This PR fixes this behavior.

What is the current behavior?

KeyDown events are consumed by the IME.

What is the updated/expected behavior with this PR?

KeyDown events are fired unconditionally, allowing the equivalent functionality of a PreviewKeyDown from WPF land, implemented as the Tunnel routing strategy.

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

Remove conditional checks before calling handleKeyDown

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 Known, but because of the location of this code it obviously needs to be carefully considered.

Obsoletions / Deprecations

N/A

Fixed issues

Fixes #15727

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048483-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

@mikeyusc,

Please read the following Contributor License Agreement (CLA). If you agree with the CLA, please reply with the following:

@cla-avalonia agree

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[mikeyusc]

@cla-avalonia agree

[mikeyusc]

Integration tests failing appears to be a tooling problem, they all pass fine on my machine.

[Gillibald]

Can you apply the requested changes?

[kekekeks]

App should never attempt to intercept keys before IME has a chance of processing those, since they don't know and can't know how IME would process events.

Keys are being pre-filtered by IME, which is consistent with other platforms.

If one wants to have a way to preview KeyDown they need to disable IME for a particular control or the entire window, that will switch Avalonia to the "traditional" KeyDown (app can do whatever it wants) -> TextInput -> KeyUp model at the cost of not supporting CJK input.

[mikeyusc]

Keys are being pre-filtered by IME, which is consistent with other platforms.

But here's the thing.. It's not consistent, even in Avalonia.. The behavior this PR supplies on MacOS is the behavior that already exists in Avalonia, on both Windows & Linux. If you run the sample app attached, you WILL get the KeyDown called before the IME processes the Input. So either this behavior is broken on the other two platforms, which I would say it is not, or it was broken on MacOS & should be restored to parity with the other two platforms.

AvaloniaTest.zip

[Gillibald]

Please use an actual IME that interacts with the keyboard

[kekekeks]

When IM is active the owner of the keyboard is IM and not the app. Apps should never react to keys that are handled by IME, because they don't have information about the way the IM handled the key (e. g. it could have been used for navigating completion list, as a hotkey, etc, etc, the app has no knowledge of this) and the app shouldn't attempt to guess if it's safe to handle the key before IME sees it, because app author can not know about all possible IM systems in the world. If app tries to mess with the external logic it has no understanding of, it leads to text input being broken.

If you are seeing a KeyDown event, it either means that IM is not active (which is the case for Linux most of the time, we only auto-enable IM for CJK locales) or that IM decided to not filter the key. With macOS IM is the only way to properly get key input with all locales, so it's always active for textboxes unless InputMethod.IsInputMethodEnabled is false.

There is a fallback to map keys to chars that is auto enabled for views that opt-out of IME, but it only works with input systems where there is 1-to-1 mapping between a key and a char.

If you want to be able to handle all KeyDown events yourself and be able to filter out TextInput events based on KeyDown events, you can disable IM via InputMethod.IsInputMethodEnabled property.

We could perhaps implement Key.ImeProcessed and KeyDown from WPF for completeness, but handling it on the app sidet will NOT prevent the key being processed by IM and apps should never use such API for triggering actions like hotkeys.