com.unity.uiwidgets/Assets/UIWidgets/widgets/focus_scope.cs

using UIWidgets.foundation;

namespace UIWidgets.widgets
{
    
    class _FocusScopeMarker: InheritedWidget {
        
        public _FocusScopeMarker( FocusScopeNode node, Widget child, Key key = null) : base(key, child)
        {
            D.assert(node != null);
            this.node = node;
        }

        public readonly FocusScopeNode node;

        public override bool updateShouldNotify(InheritedWidget oldWidget)
        {
            return node != ((_FocusScopeMarker)oldWidget).node;
        }
    }

    public class FocusScope : StatefulWidget
    {
        public FocusScope(FocusScopeNode node, Widget child, Key key = null, bool autofocus = false) : base(key)
        {
            this.node = node;
            this.child = child;
            this.autofocus = autofocus;
        }

        public readonly FocusScopeNode node;
        
        public readonly bool autofocus;
        
        public readonly Widget child;
        
        public static FocusScopeNode of(BuildContext context) {
            var scope = (_FocusScopeMarker)context.inheritFromWidgetOfExactType(typeof(_FocusScopeMarker));
            if (scope != null && scope.node != null)
            {
                return scope.node;
            }
            return context.owner.focusManager.rootScope;
        }
        
        public override State createState()
        {
            return new _FocusScopeState();
        }
    }

    class _FocusScopeState : State<FocusScope>
    {
        private bool _didAutofocus = false;
        
        public override void didChangeDependencies()
        {
            base.didChangeDependencies();
            if (!_didAutofocus && widget.autofocus)
            {
                FocusScope.of(context).setFirstFocus(widget.node);
                _didAutofocus = true;
            }
        }

        public override void dispose() {
            widget.node.detach();
            base.dispose();
        }

        public override Widget build(BuildContext context)
        {
            FocusScope.of(context).reparentScopeIfNeeded(widget.node);
            return new _FocusScopeMarker(node:widget.node, child:widget.child);
        }
    }
}