Highlighting hour and minute input fields

[flutter-zl]

This PR addresses the issue in time_picker.dart where pressing the TAB key to navigate between the hour and minute fields in input mode doesn't properly select the text in the newly focused field.

What Changed

• Added focus traversal logic in the _HourMinuteTextFieldState class's initState method that:

1. Properly handles TAB key presses to move focus to the next field
2. Automatically selects all text when a field gains focus

• Added tests in time_picker_test.dart to verify that:

1. The hour field's text is selected when it gains focus
2. Pressing TAB moves focus to the minute field
3. The minute field's text is selected when it receives focus via TAB key

Why This Matters
This change improves accessibility and usability of the time picker in input mode. When users navigate using the keyboard (pressing TAB), they expect the text in the newly focused field to be fully selected, allowing them to immediately type a new value without having to manually delete the existing text. This is standard behavior in form fields and now the TimePicker component follows this expected pattern.

Before the change:
web:
https://time-picker-0423-before-change.web.app/
mobile:
https://github.com/user-attachments/assets/532c8aa2-4f8d-4118-9eaa-2fc6c2825486

After the change:
web:
https://time-picker-04232025.web.app/
mobile:
https://github.com/user-attachments/assets/9271b3b0-9ece-479e-a01e-a62e31b1d6c7

Issue to fix:
#165830

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[mdebbar]

The changes look good to me, but I would like someone more familiar with this code to take a look. Maybe @justinmc or @Renzo-Olivares ?

[Renzo-Olivares]

In the Before web app it looks like the focus was already moving to the next field as expected when pressing the Tab key. Is this change needed?

[flutter-zl]

The expectation is the Text should be completely highlighted in both web and mobile.
Before the change
web:

After the change
web:

[Renzo-Olivares]

In the before change video it looks like focus traversal is working as expected, the focus goes to the next widget on pressing the tab key. The difference I see in the after video is that the text is completely highlighted. If focus traversal is already working do we need to add the logic in the onKey method?

[flutter-zl]

Thanks for the review! I've pushed changes to address your comments — please take another look when you have time.

[Renzo-Olivares]

I think we can use Actions here instead.

setState(() {
  // Rebuild when focus changes.
  if (kIsWeb && focusNode.hasFocus && primaryFocus?.context != null) {
    Actions.maybeInvoke(primaryFocus!.context!, SelectAllTextIntent(SelectionChangedCause.keyboard));
  }
});

[Renzo-Olivares]

I added kIsWeb because I couldn't reproduce the select all behavior on the native google calendar app timepicker on my Pixel.

[flutter-zl]

For google calendar, there are two options for time input. One is working properly. We are fixing the one that is not working properly. Please check the video. The expectation is the Text should be completely highlighted in both web and mobile.

screen-20250430-014509.mp4

[Renzo-Olivares]

In the video above it looks like google calendar's time picker does not select all text on pressing the tab key, I think we should probably try to match that behavior to be consistent with native Android/mobile unless their is some spec or guideline that says otherwise. I agree that on all web platforms we should add the select all behavior since that is the default behavior or single line inputs.

[flutter-zl]

Good catch. Yes. I agree. I will make the implementation web only.

[Renzo-Olivares]

Instead of having the if branches for kIsWeb we can use skip: !kIsWeb to skip the test entirely if the platform is not web, it is a parameter on testWidgets.

[flutter-zl]

Great. Thanks for this suggestions. I have made the changes. Please review.

[Renzo-Olivares]

The analyzer is complaining that we need to add a const here.

[Renzo-Olivares]

LGTM modulo the analyzer issue.