Flutter TextField+Dialog 键盘闪烁

Dialog中需要使用输入框，新建类继承自AlertDialog，使用时发现，键盘一直闪烁。

class TextFiledWrongDialog extends AlertDialog {
  final GlobalKey<FormFieldState<String>> _passwordFieldKey = GlobalKey<FormFieldState<String>>();

  @override
  Widget get content => Material(
        child: Wrap(
          children: <Widget>[
            Column(
              children: <Widget>[
                Text("Test Wrong Dialog"),
                TextFormField(
                  key: _passwordFieldKey,
                  autofocus: true,
                )
              ],
            )
          ],
        ),
      );
}

原因是AlertDialog继承自StatelessWidget,而事实上需要状态改变，所以必须将content变成StatefulWidget。

class AlertDialog extends StatelessWidget

完整示例代码：

import 'package:flutter/material.dart';

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

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

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Demo'),
      ),
      body: Column(
        children: <Widget>[
          RaisedButton(
            child: Text("Show Wrong dialog"),
            onPressed: () {
              showDialog(context: context, builder: (_) => TextFiledWrongDialog());
            },
          ),
          RaisedButton(
            child: Text("Show Right dialog"),
            onPressed: () {
              showDialog(context: context, builder: (_) => TextFiledRightDialog());
            },
          )
        ],
      ),
    );
  }
}

class TextFiledWrongDialog extends AlertDialog {
  final GlobalKey<FormFieldState<String>> _passwordFieldKey = GlobalKey<FormFieldState<String>>();

  @override
  Widget get content => Material(
        child: Wrap(
          children: <Widget>[
            Column(
              children: <Widget>[
                Text("Test Wrong Dialog"),
                TextFormField(
                  key: _passwordFieldKey,
                  autofocus: true,
                )
              ],
            )
          ],
        ),
      );
}

class TextFiledRightDialog extends AlertDialog {
  final GlobalKey<FormFieldState<String>> _passwordFieldKey = GlobalKey<FormFieldState<String>>();

  @override
  Widget get content => DialogContent();
}

class DialogContent extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => DialogContentState();
}

class DialogContentState extends State<DialogContent> {
  final GlobalKey<FormFieldState<String>> _passwordFieldKey = GlobalKey<FormFieldState<String>>();

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Wrap(
        children: <Widget>[
          Column(
            children: <Widget>[
              Text("Test Right Dialog"),
              TextFormField(
                key: _passwordFieldKey,
                autofocus: true,
              )
            ],
          )
        ],
      ),
    );
  }
}