CallBack Function

 import "package:flutter/material.dart";

void main()
{
  runApp(const MyApp());
}

class MyApp extends StatelessWidget
{
  const MyApp({super.key});

  @override
  Widget build(BuildContext context)
  {
    return MaterialApp(
      title: "Hello",
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const FlutterApp(),
    );
  }
}

class FlutterApp extends StatefulWidget
{
  const FlutterApp({super.key});

  @override
  State<StatefulWidget> createState()
  {
    return FlutterState();
  }
}

class FlutterState extends State<FlutterApp>
{
  callBack(){
    print("Clicked button");
  }
  @override
  Widget build(BuildContext context)
  {
    return Scaffold(
      drawer: const Drawer(),
      appBar: AppBar(
        title: const Text("Hello Flutter CallBack",
          style: TextStyle(fontWeight: FontWeight.bold),
        ),
        centerTitle: true,
        backgroundColor: Colors.grey,
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: callBack,  /*To manage Data passing or Data flow throughout the flutter application, callBack
                                  function is used.*/
          style: ElevatedButton.styleFrom(
            backgroundColor: Colors.blue,
            fixedSize: const Size(350.0,50.0),
          ),
          child: const Text("Clicked me!!",
            style: TextStyle(fontWeight: FontWeight.bold, color: Colors.white, fontSize: 20.0),
          ),
        ),
      ),
    );
  }
}