모든 코드가 똑같은것같은데 버튼이 작동되지않습니다.

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}
class MyApp extends StatelessWidget {


  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ShowHide(),
    );
  }
}
class ShowHide extends StatefulWidget {
  @override
  _ShowHideState createState() => _ShowHideState();
}

class _ShowHideState extends State<ShowHide> {

  @override

  Widget build(BuildContext context) {
    bool visible_val=true;

    void showWidget() {
      setState(() {
        visible_val = true;
      });
    }

      void hideWidget() {
        setState(() {
          visible_val = false;
        });
      }
    return Scaffold(
      appBar: AppBar(
        title: Text("show hide"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              child: Text("Show"),
              onPressed: showWidget,
            ),
            RaisedButton(
            child: Text("Hide"),
            onPressed: hideWidget,
            ),
            Visibility(visible: visible_val,
            child: Text("This is text",
            style: TextStyle(fontSize: 30.0),
            ),
            ),
          ],
        ),
      ),
    );
  }
}