Enable navigation using the keyboard

[bdlukaa]

Currently, we can only navigate using the mouse. This can be achieved using the FocusManager class:

...state with WidgetsBindingObserver

  bool _hasPrimaryFocus = false;
  late FocusHighlightMode _focusHighlightMode;

  void _handleFocusHighlightModeChange(FocusHighlightMode mode) {
    if (!mounted) {
      return;
    }
    setState(() {
      _focusHighlightMode = mode;
    });
  }

  void _handleFocusChanged() {
    if (_hasPrimaryFocus != focusNode!.hasPrimaryFocus) {
      setState(() {
        _hasPrimaryFocus = focusNode!.hasPrimaryFocus;
      });
    }
  }

  @override
  void initState() {
    super.initState();
    focusNode!.addListener(_handleFocusChanged);
    final FocusManager focusManager = WidgetsBinding.instance!.focusManager;
    _focusHighlightMode = focusManager.highlightMode;
    focusManager.addHighlightModeListener(_handleFocusHighlightModeChange);
  }

  @override
  void dispose() {
    WidgetsBinding.instance!.removeObserver(this);
    WidgetsBinding.instance!.focusManager.removeHighlightModeListener(_handleFocusHighlightModeChange);
    focusNode!.removeListener(_handleFocusChanged);
    super.dispose();
  }

  bool get _showHighlight {
    switch (_focusHighlightMode) {
      case FocusHighlightMode.touch:
        return false;
      case FocusHighlightMode.traditional:
        return _hasPrimaryFocus;
    }
  }

This code is from flutter/dropdown

If _showHighlight is true, we should change the widget decoration.

[bdlukaa]

This was implemented in 1.7.1 using the widget FocusableActionDetector. All the inputs can now be focused using the keyboard, and be pressed using enter and space. The widget NavigationPaneBody was improved so that focus doesn't feel weird