Flutter中文本字段中的文本垂直居中

我无法使用提供的主题数据和有限的代码重现此错误.请发布整个build()函数.Here's what I'm seeing with this code and version

flutter --version

Flutter 0.4.4 • channel beta • https://github.com/flutter/flutter.git
Framework • revision f9bb4289e9 (3 weeks ago) • 2018-05-11 21:44:54 -0700
Engine • revision 06afdfe54e
Tools • Dart 2.0.0-dev.54.0.flutter-46ab040e58

Main.Dart:

import 'package:flutter/material.dart';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        fontFamily: 'Product Sans',
        brightness: Brightness.dark,
        buttonColor: Colors.green[300],
        accentColor: Colors.green[300],
        scaffoldBackgroundColor: Colors.blueGrey[900],
        canvasColor: Colors.blueGrey[900],
        textSelectionColor: new Color.fromRGBO(81, 107, 84, 0.8),
        bottomAppBarColor: Colors.blueGrey[800],
        primaryColor: Colors.blueGrey[900],
        indicatorColor: Colors.green[300],
        cardColor: Colors.white,
        highlightColor: Colors.green[300],
        errorColor: Colors.red[400],
        textSelectionHandleColor: Colors.green[300],
        splashColor: Colors.white10,
        buttonTheme: new ButtonThemeData(
            shape: new RoundedRectangleBorder(
                borderRadius: new BorderRadius.circular(22.0))),
        inputDecorationTheme: new InputDecorationTheme(
            contentPadding:
                new EdgeInsets.symmetric(horizontal: 10.0, vertical: 10.0),
            border: new OutlineInputBorder(
                gapPadding: 3.0,
                borderRadius: new BorderRadius.circular(22.0))),
      ),
      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) {
    TextEditingController controller = new TextEditingController();
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Padding(
        padding: const EdgeInsets.symmetric(vertical: 8.0),
        child: new TextFormField(
          maxLines: 1,
          controller: controller,
          validator: (value) {
            if (value.isEmpty) {
              return 'Please enter username.';
            }
          },
          decoration: new InputDecoration(
              labelText: 'Username',
              suffixIcon: new IconButton(
                highlightColor: Colors.transparent,
                icon: new Container(width: 36.0, child: new Icon(Icons.clear)),
                onPressed: () {
                  controller.clear();
                },
                splashColor: Colors.transparent,
              ),
              prefixIcon: new Icon(Icons.account_circle)),
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}