Dispose widget when navigating to new route

Question

I have two screens in my app.

Screen A runs a computationally expensive operation while opened, and properly disposes by cancelling animations/subscriptions to the datab

Answer 1

call Navigator.pushReplacement when routing between first and second screen.

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    title: 'Navigation Basics',
    home: FirstRoute(),
  ));
}

class FirstRoute extends StatefulWidget {
  @override
  _FirstRouteState createState() => _FirstRouteState();
}

class _FirstRouteState extends State {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('First Route'),
      ),
      body: RaisedButton(
        child: Text('Open route'),
        onPressed: () {
          Navigator.pushReplacement(
            context,
            MaterialPageRoute(builder: (context) => SecondRoute()),
          );
        },
      ),
    );
  }

  @override
  void dispose() {
    // Never called
    print("Disposing first route");
    super.dispose();
  }
}

class SecondRoute extends StatefulWidget {
  @override
  _SecondRouteState createState() => _SecondRouteState();
}

class _SecondRouteState extends State {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Second Route"),
      ),
      body: RaisedButton(
        onPressed: () {
          Navigator.pushReplacement(
            context,
            MaterialPageRoute(builder: (context) => FirstRoute()),
          );
        },
        child: Text('Go back!'),
      ),
    );
  }

  @override
  void dispose() {
    print("Disposing second route");
    super.dispose();
  }
}

Try this