drop_down_menu.dart

class DropdownMenu extends StatefulWidget {
  const DropdownMenu({
    super.key,
    required this.name,
    required this.child,
    required this.overlayBuilder,
  });

  final String name;
  final Widget child;

  /// Has access to the portal controller via a provider.
  final WidgetBuilder overlayBuilder;

  @override
  State<DropdownMenu> createState() => _DropdownMenuState();

  static OverlayPortalController of(BuildContext context) {
    final _ControllerInjector? result =
        context.dependOnInheritedWidgetOfExactType<_ControllerInjector>();
    assert(result != null, 'No OverlayController found in context');
    return result!.controller;
  }

  static OverlayPortalController? maybeOf(BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<_ControllerInjector>()
        ?.controller;
  }
}

class _DropdownMenuState extends State<DropdownMenu> {
  final OverlayPortalController controller = OverlayPortalController();

  final LayerLink link = LayerLink();

  @override
  Widget build(BuildContext context) {
    return _ControllerInjector(
      controller: controller,
      child: OverlayPortal(
        controller: controller,
        child: CompositedTransformTarget(
          link: link,
          child: IconButton(
            onTap: () {
              setState(() {
                controller.show();
                setState(() {});
              });
            },
            child: widget.child,
          ),
        ),
        overlayChildBuilder: (context) {
          // This is a semi-transparent background that will dismiss the
          // overlay when tapped.
          return GestureDetector(
            onTap: () {
              setState(() {
                controller.hide();
              });
            },
            child: Container(
              color: Theme.of(context).colorScheme.shadow,
              child: CompositedTransformFollower(
                link: link,
                targetAnchor: Alignment.bottomRight,
                followerAnchor: Alignment.topRight,
                // Dummy tappable as a workaround to:
                // https://github.com/flutter/flutter/issues/144221
                // This prevents the parent gesture detector from dismising the
                // overlay when Flutter erroneously calls it when the user
                // interrupts scroll momentum by tapping on the list view.
                child: GestureDetector(
                  onTap: () {},
                  // This is the content of the drop down menu, typically a ListView.
                  child: widget.overlayBuilder(context),
                ),
              ),
            ),
          );
        },
      ),
    );
  }
}

class _ControllerInjector extends InheritedWidget {
  const _ControllerInjector({
    required super.child,
    required this.controller,
  });

  final OverlayPortalController controller;

  @override
  bool updateShouldNotify(_ControllerInjector old) {
    return old.controller != controller;
  }
}