dart，flutter - ListView没有显示

Question

我正在尝试显示ListView但它没有出现，下面是完整的代码（打开带有材质页面路径的屏幕）：

pvc_screen.dart：

import 'package:flutter/material.dart';

class PVCScreen extends StatefulWidget {
  @override
  _PVCScreenState createState() => _PVCScreenState();
}

class _PVCScreenState extends State<PVCScreen> {
  List<String> currencyPairs = ['EUR/USD', 'GBP/USD', 'USD/JPY'];
  List<String> currencies = ['USD', 'GBP', 'JPY'];

  String currencyPair = 'EUR/USD';
  String askPrice = '';
  String units = '';
  String accountCurrency = 'USD';
  String result = '';

  double dots;

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Pip Value Calculator'),
      ),
      body: ListView(children: <Widget>[
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: ListTile(
            title: new Text('Currency Pair'),
            subtitle: DropdownButton(
              value: currencyPair,
              items: <DropdownMenuItem<String>>[
                DropdownMenuItem(
                  value: currencyPairs[0],
                  child: new Text('${currencyPairs[0]}'),
                ),
                DropdownMenuItem(
                  value: currencyPairs[1],
                  child: new Text('${currencyPairs[1]}'),
                ),
                DropdownMenuItem(
                  value: currencyPairs[2],
                  child: new Text('${currencyPairs[2]}'),
                ),
              ],
              onChanged: (String value) {
                setState(() {
                  currencyPair = value;
                });
              },
            ),
          ),
        ),
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: ListTile(
              title: new Text('Ask Price'),
              subtitle: new TextField(
                controller: TextEditingController(text: '$askPrice'),
                decoration: InputDecoration(hintText: '0'),
                onChanged: (String text) {
                  setState(() {
                    askPrice = text;
                  });
                },
              )),
        ),
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: ListTile(
              title: new Text('Position Size (units)'),
              subtitle: new TextField(
                controller: TextEditingController(text: '$units'),
                decoration: InputDecoration(hintText: '0'),
                onChanged: (String text) {
                  setState(() {
                    units = text;
                  });
                },
              )),
        ),
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: ListTile(
            title: new Text('Account Currency'),
            subtitle: DropdownButton(
              value: accountCurrency,
              items: <DropdownMenuItem<String>>[
                DropdownMenuItem(
                  value: currencies[0],
                  child: new Text('${currencies[0]}'),
                ),
                DropdownMenuItem(
                  value: currencies[1],
                  child: new Text('${currencies[1]}'),
                ),
                DropdownMenuItem(
                  value: currencies[2],
                  child: new Text('${currencies[2]}'),
                ),
              ],
              onChanged: (String value) {
                setState(() {
                  accountCurrency = value;
                });
              },
            ),
          ),
        ),
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: Center(
            child: MaterialButton(
              child: new Text('Calculate'),
              onPressed: () {
                setState(() {
                  dots = currencyPair.split('/')[1] == 'JPY' ? 0.01 : 0.0001;

                  result = (dots.toInt() / int.parse('$askPrice')).toString();
                });
              },
            ),
          ),
        ),
        Padding(
          padding: const EdgeInsets.all(10.0),
          child: Center(
              child: new Text(
            '\$$result',
            style: TextStyle(fontSize: 24.0),
          )),
        ),
      ]),
    );
  }
}

所有代码在我眼中看起来都很有效。代码很简单PVCScreen是一个StatefulWidget。在它的Build覆盖下，有Scaffold有AppBar和body，body有一个ListView和不同的项目ListTiles，现在问题是AppBar正在显示（出现）但是body（ListView）没有显示（隐藏）。我希望AppBar和ListView都可见。

Answer 1

您不能将TextField用作ListTile中的副标题（使用当前实现）。

问题已经在github上开放：https://github.com/flutter/flutter/issues/18755