How To Override the “Back” button in Flutter?

On my Home widget, when user taps system back button, I want to show a confirmation dialog asking “Do you want to exit the App?”

I don’t understand how I should override or handle the system back button.

You can use WillPopScope:

import 'dart:async';

import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  HomePage({Key key, this.title}) :super(key: key);

  final String title;

  State<StatefulWidget> createState() => new _HomePageState();

class _HomePageState extends State<HomePage> {

  Future<bool> _onWillPop() {
    return showDialog(
      context: context,
      builder: (context) => new AlertDialog(
        title: new Text('Are you sure?'),
        content: new Text('Do you want to exit an App'),
        actions: <Widget>[
          new FlatButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: new Text('No'),
          new FlatButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: new Text('Yes'),
    ) ?? false;

  Widget build(BuildContext context) {
    return new WillPopScope(
      onWillPop: _onWillPop,
      child: new Scaffold(
        appBar: new AppBar(
          title: new Text("Home Page"),
        body: new Center(
          child: new Text("Home Page"),