class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  final FocusNode myFocusNode = FocusNode();
  final TextEditingController controller = TextEditingController();

  @override
  void dispose() {
    myFocusNode.dispose();
    controller.dispose();
    super.dispose();
  }

  void _unfocusTextField() {
    myFocusNode.unfocus();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        TextField(
          controller: controller,
          focusNode: myFocusNode,
        ),
        ElevatedButton(
          onPressed: _unfocusTextField,
          child: Text("Unfocus"),
        ),
      ],
    );
  }
}

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