vijaybhaiflutter.dart

import 'package:flutter/material.dart';
void main()
{
  runApp(new HelloWorld());
}

class HelloWorld extends StatefulWidget {
  @override
  _HelloWorldState createState() => _HelloWorldState();
}
class _HelloWorldState extends State<HelloWorld> {

  String mytext = "Hello World";
   void goodbyeText()
   {
     setState((){
       this.mytext = "GoodBye World";
     });
   print("inside goodbye text")  ;
   print (this.mytext);  
 }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Hello'),
        ),
        body:Center(
        child:FlatButton(
      color: Colors.blue,
      textColor:Colors.lightGreenAccent,
          onPressed:(){},
        child:Text(
        "1"
        ),
        ),
        ),
        
      ),
    );
  }
}