Flutter onChange of TextField getting call on keyboard hide (via back press)

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _value = "Here we go...";

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Container(
            child: Column(
              children: [
                SizedBox(height: 20),
                TextField(
                  decoration: new InputDecoration(
                    labelText: "Enter something to reflect",
                    fillColor: Colors.white,
                    border: new OutlineInputBorder(
                      borderRadius: new BorderRadius.circular(15.0),
                      borderSide: new BorderSide(),
                    ),
                  ),
                  onChanged: (value) {
                    ScaffoldMessenger.of(context).showSnackBar(SnackBar(
                      content: Text("${"Changed Value : "} : " + value),
                      duration: Duration(milliseconds: 100),
                    ));
                    setState(() {
                      _value += "\n" + value;
                    });
                  },
                  keyboardType: TextInputType.streetAddress,
                ),
                SizedBox(height: 20),
                Expanded(flex: 1, child: SingleChildScrollView(child: Text(_value))),
              ],
            ),
          ),
        ),
      ),
    );
  }
}