How to deactivate or override the Android "BACK" button, in Flutter?

Is there a way to deactivate the Android back button when on a specific page?

class WakeUpApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: "Time To Wake Up ?",
      home: new WakeUpHome(),
      routes: <String, WidgetBuilder>{
        '/pageOne': (BuildContext context) => new pageOne(),
        '/pageTwo': (BuildContext context) => new pageTwo(),
      },
    );
  }
}

On pageOne I have a button to go to pageTwo:

new FloatingActionButton(
  onPressed: () {    
    Navigator.of(context).pushNamed('/pageTwo');
  },
)

My problem is that if I press the Back arrow at the bottom of the android screen, I go back to pageOne. I would like this button to not show up at all. Ideally, I would like to have no possible way out of this screen unless the user for example keeps his finger pressed on the screen for 5 seconds. (I am trying to write an App for toddlers, and would like only the parents to be able to navigate out of the particular screen).

The answer is WillPopScope. It will prevent the page from being popped by the system. You'll still be able to use Navigator.of(context).pop()

@override
Widget build(BuildContext context) {
  return new WillPopScope(
    onWillPop: () async => false,
    child: new Scaffold(
      appBar: new AppBar(
        title: new Text("data"),
        leading: new IconButton(
          icon: new Icon(Icons.ac_unit),
          onPressed: () => Navigator.of(context).pop(),
        ),
      ),
    ),
  );
}

As Rémi Rousselet pointed out, WillPopScope is usually the way to go. However, if you are developing a stateful widget that should react to the back button directly, you may use this:

https://pub.dartlang.org/packages/back_button_interceptor

Note: I am the author of this package.

While Remi's answer is right, usually you don't want to simply block the back button but want a user to confirm the exit.

You can do it similar way by getting an answer from the confirmation dialog, because onWillPop is a future.

@override
Widget build(BuildContext context) {
  return WillPopScope(
    child: Scaffold(...),
    onWillPop: () => showDialog<bool>(
      context: context,
      builder: (c) => AlertDialog(
        title: Text('Warning'),
        content: Text('Do you really want to exit'),
        actions: [
          FlatButton(
            child: Text('Yes'),
            onPressed: () => Navigator.pop(c, true),
          ),
          FlatButton(
            child: Text('No'),
            onPressed: () => Navigator.pop(c, false),
          ),
        ],
      ),
    ),
  );
}

How to deactivate or override the Android "BACK" button, in Flutter?

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