How can I render only one Widget setState - dart

Question

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.

Answer 1

I am having a bit of trouble understanding your question, but I also understand that English is not your first language. You seem to be asking, "How can I render only one button for example #2?". Please let me know if this is not your question so that I, and others, can help you.
This will only render one button,
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>[
RaisedButton(
onPressed: () {
setState(() {
istrue = !istrue;
});
},
child: Text('Click me'),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(istrue ? 'Boo!' : ''),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(istrue ? 'Boo!' : ''),
),
],
)),
);
}
}

Answer 2

You are calling a Column widget within another Column widget in the Scaffold widget in your second example. Why would you do that? There are many ways to structure that layout in the flutter API.
You can't have a new Column(new Column(...)); Its redundant.
Edit:
I pulled this from the flutter website at Column class:
The Column widget does not scroll (and in general it is considered an error to have more children in a Column than will fit in the available room). If you have a line of widgets and want them to be able to scroll if there is insufficient room, consider using a ListView.