Widget's didUpdateWidget method called when screen rotates with MaterialApp routes

Question

When I use routes in MaterialApp the child widget's (MyHomePage) didUpdateWidget is called whenever I rotate the screen/open the keyboard etc.

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      routes: {
        '/': (_) => MyHomePage(title: 'Flutter Demo Home Page'),
      },
      initialRoute: '/',
    );
  }
}

On the other hand, when I use the home parameter, didUpdateWidget is not called when I rotate the screen/open the keyboard.

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

The issue I have is that I am using the Bloc pattern sample as a guide so my Bloc is disposed and recreated whenever the didUpdateWidget is called. This means I lose all my app's state that is in the Bloc, e.g. what is selected.

@override
void didUpdateWidget(ProductSquare oldWidget) {
    super.didUpdateWidget(oldWidget);
    _disposeBloc();
    _createBloc();
}

Why is there a difference is behavior between using routes and home? How can I make routes behave like home and not call didUpdateWidget when the screen is rotated so the bloc is not unnecessarily recreated?

Full app sample without Bloc that rebuilds whenever I rotate the screen.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      routes: {
        '/': (_) => MyHomePage(title: 'Flutter Demo Home Page'),
      },
      initialRoute: '/',
    );
  }
}

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  void didUpdateWidget(MyHomePage oldWidget) {
    super.didUpdateWidget(oldWidget);

    print('didUpdateWidget');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

Answer 1

The issue I have is that I am using the Bloc pattern sample as a guide so my Bloc is disposed and recreated whenever the didUpdateWidget is called. This means I lose all my app's state that is in the Bloc, e.g. what is selected.

This is the problem. Don't do that, it is anti-pattern.

Any widgets you make should keep in mind that they can theoretically be updated thousands of time with no change. You're supposed to verify that something changed before performing side-effects.

As such your didUpdateWidget should be as followed:

@override
void didUpdateWidget(ProductSquare oldWidget) {
  super.didUpdateWidget(oldWidget);
  if (widget.product != oldWidget.product) {
    _disposeBloc();
    _createBloc();
  }
}