Dart 在Flatter中导航后，无法关注新页面中的文本字段

由于某些原因，我无法在导航后转到下一页后专注于TextField.当 Select TextField时，键盘将自动关闭.如果我在TextField上设置autofocus: true，那么键盘将无限弹出并立即反复关闭.

当我的应用程序大小合理时，我遇到了这个问题，但我能够在一个最小的示例应用程序中重新创建它.

我将Dart 2.0.0-dev.55.0与Flutter beta v0一起使用.3.2.

主页代码:

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'),
            ),
          ],
        ),
      ),
    );
  }
}

以下是包含TextField的页面的代码.

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(),
        ],
      ),
    );
  }
}

如果我把TextField放在主页上，我可以很好地聚焦在那里，但不能放在Settings页面中的TextField上.我想这和键盘没有优先于弹出的页面有关吧？还是怎么回事？如何让应用程序只关注导航页面上的输入字段？