Flutter/Dart: A TextEditingController was used after being disposed

Question

Please, someone, help on this, I am not sure if this is a framework glitch then how are there not more post on this and if it is me then how come there is not much on this error!

=========================== main.dart

import 'package:flutter/material.dart';
import 'dialog_reusable.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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
  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.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          showDialog( context: context, builder: (context) { return MyDialog(); });
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

=========================== dialog_reusable.dart

import 'package:flutter/material.dart';

import 'dialog_reusable.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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
  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.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          showDialog( context: context, builder: (context) { return MyDialog(); });
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

===========================

===========================

Steps to Reproduce

0. The Textfield is part of a Dialog() along with 2 buttons 'ok' and 'cancel'
1. Create a new Flutter project with standard options
2. Remove the files in LIB folder
3. Make new files with the code and name provided above
4. When the Dialog() pops up and the 'cancel' button is clicked the following error happens.

---

════════ Exception caught by widgets library ════════

The following assertion was thrown building MouseRegion(listeners: [enter, exit], state: _MouseRegionState#1877d): A TextEditingController was used after being disposed.

Once you have called dispose() on a TextEditingController, it can no longer be used.

The relevant error-causing widget was: TextField file:///C:/MobileApps/Apps/Clima-Flutter/lib/utilities/mydialog.dart:90:15

When the exception was thrown, this was the stack:

#0 ChangeNotifier._debugAssertNotDisposed. (package:flutter/src/foundation/change_notifier.dart:106:9)

#1 ChangeNotifier._debugAssertNotDisposed (package:flutter/src/foundation/change_notifier.dart:112:6)

#2 ChangeNotifier.removeListener (package:flutter/src/foundation/change_notifier.dart:167:12)

#3 _AnimatedState.didUpdateWidget (package:flutter/src/widgets/transitions.dart:159:28)

#4 StatefulElement.update (package:flutter/src/widgets/framework.dart:4690:58)

---

Steps Tried:

1. Disable the Textfield before Dispose() by using a variable in 'enable' property of Textfield
2. Assign NULL to 'Controller' property of TextField if the variable that holds enable property for TextField is false before Dispose(), via the ternary operator and if clause
3. Assign NULL to 'onChanged:' property of TextField if the variable that holds enable property for TextField is false before Dispose(), via the ternary operator and if clause