【Flutter】親 Widget と子 Widget 間でメソッドを参照する方法

class ChildWidget extends StatefulWidget {
  final Function callback;
  const ChildWidget({Key? key, required this.callback}) : super(key: key);

  @override
  State<ChildWidget> createState() => _ChildWidgetState();
}

class _ChildWidgetState extends State<ChildWidget> {

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: ()=> widget.callback('child'),
      child: const Text('print'),
    );
  }
}

class ParentWidget extends StatelessWidget {
  const ParentWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('Method path between Parent and Child'),
        ),
        body: ChildWidget(callback: printOnParent),
    );
  }

  void printOnParent(String from) {
    debugPrint('call parent method from $from');
  }
}

class ChildWidget extends StatefulWidget {
  const ChildWidget({Key? key}) : super(key: key);

  @override
  State<ChildWidget> createState() => ChildWidgetState();
}

class ChildWidgetState extends State<ChildWidget> {

  @override
  Widget build(BuildContext context) {
    return const Text('Child Widget');
  }

  void printOnChild(String from) {
    debugPrint('call child method from $from');
  }
}

class ParentWidget extends StatelessWidget {
  const ParentWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    const key = GlobalObjectKey<ChildWidgetState>('child');

    return Scaffold(
        appBar: AppBar(
          title: const Text('Method path between Parent and Child'),
        ),
        body: Column(
          children: [
            const ChildWidget(key: key),
            ElevatedButton(
              onPressed: ()=> key.currentState?.printOnChild('parent'),
              child: const Text('print'),
            )
          ],
        ),
    );
  }
}