I have two easy basics example one is Works and second need some of explaining.
So, When I Clik Button in Example one it Works and setStaet rendering the page.

Second Example I using a body function that has setState of Button. When I click button nothing happen even with using setState notes if 
 the variable inside the parenthesis it does not render.
When I make Variable instance in class it works fine but I need to rendering Only One Button how?

Full code Example One 

```
import 'package:flutter/material.dart';

main() => runApp(MaterialApp(
      home: Home(),
    ));

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  bool istrue = false;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Works fine'),),
      body: Center(child: body()),
    );
  }

  Widget body() {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            setState(() {
              istrue = !istrue;
            });
          },
          child: Text('Click me'),
        ),
        Padding(
          padding: const EdgeInsets.all(8.0),
          child: Text(istrue ? 'Boo!' : ''),
        ),
      ],
    );
  }
}

```

Full code Example two

```
import 'package:flutter/material.dart';

main() => runApp(MaterialApp(
  home: Home(),
));

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  bool istrue = false;
  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(title: Text('Works fine'),),
      body: Center(child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          body(),body(),
        ],
      )),
    );
  }

  Widget body() {

    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            setState(() {
              istrue = !istrue;
            });
          },
          child: Text('Click me'),
        ),
        Padding(
          padding: const EdgeInsets.all(8.0),
          child: Text(istrue ? 'Boo!' : ''),
        ),
      ],
    );
  }
}

```

Thanks as sky.