Cannot focus on TextField in new page after navigating in Flutter

Question

For some reason, I cannot focus on a TextField after on the next page after navigating. The keyboard would automatically dismiss when the TextField is selected. If I set autofocus: true on the TextField, then the keyboard will infinitely popup and immediately dismiss over and over again.

I encountered this when my app was a reasonable size but I was able to recreate this in a minimal example app.

I am using Dart 2.0.0-dev.55.0 with Flutter beta v0.3.2.

Code for main page:

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

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('Helpful text.',),
            // ===== Where navigation happens =====
            RaisedButton(
              onPressed: () {
                Navigator.push(context, PageRouteBuilder(
                  pageBuilder: (_, __, ___) => SettingsPage()));
              },
              child: Text('Go to input page'),
            ),
          ],
        ),
      ),
    );
  }
}

Here is the code for the page with the TextField.

import 'package:flutter/material.dart';

class SettingsPage extends StatefulWidget {
  SettingsPage({Key key}) :
   super(key: key);

  @override
  _SettingsPage createState() => new _SettingsPage();
}


class _SettingsPage extends State<SettingsPage> {

  @override
  Widget build(BuildContext context) {
    final key = GlobalKey<ScaffoldState>();
    return Scaffold(
      key: key,
      backgroundColor: Colors.white,
      appBar: AppBar(
        title: Text("Settings"),
      ),
      body: ListView(
        children: <Widget>[
          Text("Enter something"),
          // Can't focus on this widget
          TextField(),
        ],
      ),
    );
  }
}

I can focus fine on TextField on the main page if I put one there, but can't on the one in the Settings page. I assume it has something to do with the keyboard not taking priority over the popped up page? Or what is going on? How I can get the app to just focus on input fields on a navigated page?

Answer 1

So the problem comes from the fact that I am supplying the GlobalKey to the Scaffold. Removing the key solves the issue. Not exactly sure why but the issue is mostly explained in this Github issue.

I was using the key to have snackbar popup when showing an error message when validating the input but now I'm opting to just display the error message in a Text widget.