我正在与这个 DropDownItem 框错误作斗争，一切似乎都正常，但在加载时弹出黄色越界。尝试了几件事，但无法解决。我的 Widget 有这段代码。

@override
Widget build(BuildContext context) {
    var _children = <Widget>[
      !_createNew ? _referrerPractice() : _referrerCreate(),
    ];
    return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
        body: new Column(
          mainAxisSize: MainAxisSize.max,
          children: _children,
        ));
  }

然后我将其用作函数之一。

Widget _referrerPractice() {
assert(!_createNew);
return new Form(
  key: _formKey2,
  child: new Expanded(
    child: new ListView(
      padding: const EdgeInsets.symmetric(horizontal: 16.0),
      children: <Widget>[
        new InputDecorator(
          decoration: const InputDecoration(
            labelText: 'Referrer Practice',
            hintText: 'Choose Referrer Practice or choose new',
          ),
          isEmpty: _referPractice == null,
          child: new DropdownButton<String>(
            value: _referPractice,
            isDense: true,
            onChanged: (String newValue) {
              setState(() {
                _referPractice = newValue;
              });
            },
            items: practicelist.map((Map value) {
              return new DropdownMenuItem<String>(
                value: value['id'].toString(),
                child: new Text(value['name']),
              );
            }).toList(),
          ),
        ),
        new RaisedButton(
            child: new Text('Start'), onPressed: _startReferrer),
      ],
    ),
  ),
);

它似乎在另一个页面上工作，我没有使用函数来填充小部件，只是一个常规的小部件变量，但看起来它应该是相同的，因为结构是相同的。

知道我遗漏了什么吗？这是一个 DropDownButton，但它发生在具有 DropDownButton 以及其他功能的结果页面上。

编辑************ 这是工作代码

final List<String> _allTypeAppt = <String>['Elective OP', 'Hospital Transfer', 'Phone Consult'];

new Form(
      key: _formKey,
      autovalidate: _autovalidate,
      onWillPop: _warnUserAboutInvalidData,
      child: new Expanded(
          child: new ListView(
            padding: const EdgeInsets.symmetric(horizontal: 16.0),
            children: <Widget>[
              new TextFormField(
                decoration: const InputDecoration(
                  icon: const Icon(Icons.person),
                  hintText: 'First Name?',
                  labelText: 'First Name *',
                ),
                controller: _fnameController,

                onSaved: (String value) { referral.fname = value; },
                validator: _validateName,
              ),

              new TextFormField(
                decoration: const InputDecoration(
                  icon: const Icon(Icons.person),
                  hintText: 'Last Name?',
                  labelText: 'Last Name *',
                ),
                controller: _lnameController,
                onSaved: (String value) { referral.lname = value; },
                validator: _validateName,
              ),

              new _DateTimePicker(
                labelText: 'DOB',
                selectedDate: _fromDate,
                selectDate: (DateTime date) {
                  setState(() {
                    _fromDate = date;
                  });
                },
              ),

              new TextFormField(
                decoration: const InputDecoration(
                    icon: const Icon(Icons.phone),
                    hintText: 'How to contact?',
                    labelText: 'Phone Number *',
                ),
                controller: _phoneController,
                keyboardType: TextInputType.phone,
                onSaved: (String value) { referral.contact = value; },
                validator: _validatePhoneNumber,
                // TextInputFormatters are applied in sequence.
                /*inputFormatters: <TextInputFormatter> [
                  WhitelistingTextInputFormatter.digitsOnly,
                  // Fit the validating format.
                  _phoneNumberFormatter,
                ],*/
              ),

              new TextFormField(
                decoration: const InputDecoration(
                  icon: const Icon(Icons.phone),
                  hintText: 'Alt contact?',
                  labelText: 'Alt Phone Number *',
                ),
                controller: _altPhoneController,
                keyboardType: TextInputType.phone,
                onSaved: (String value) { referral.altcontact = value; },
                validator: _validatePhoneNumber,
                // TextInputFormatters are applied in sequence.
                /*inputFormatters: <TextInputFormatter> [
                  WhitelistingTextInputFormatter.digitsOnly,
                  // Fit the validating format.
                  _phoneNumberFormatter,
                ],*/
              ),

              new TextFormField(
                decoration: const InputDecoration(
                  icon: const Icon(Icons.email),
                  hintText: 'Patien Email?',
                  labelText: 'Patient Email *',
                ),
                controller: _emailController,
                onSaved: (String value) { referral.altcontact = value; },
                //validator: _validatePhoneNumber,
                // TextInputFormatters are applied in sequence.
                /*inputFormatters: <TextInputFormatter> [
                  WhitelistingTextInputFormatter.digitsOnly,
                  // Fit the validating format.
                  _phoneNumberFormatter,
                ],*/
              ),

              new TextFormField(
                decoration: const InputDecoration(
                  hintText: 'Tell us about patient',
                  helperText: 'It does not have to be detailed yet',
                  labelText: 'Referral Details',
                ),
                controller: _detailsController,
                maxLines: 5,
              ),

              new InputDecorator(
                decoration: const InputDecoration(
                  labelText: 'Type of Appointment',
                  hintText: 'Choose an Appointment Type',
                ),
                isEmpty: _typeAppt == null,
                child: new DropdownButton<String>(
                  value: _typeAppt,
                  isDense: true,
                  onChanged: (String newValue) {
                    setState(() {
                      _typeAppt = newValue;
                    });
                  },
                  items: _allTypeAppt.map((String value) {
                    return new DropdownMenuItem<String>(
                      value: value,
                      child: new Text(value),
                    );
                  }).toList(),
                ),
              ),

              new RaisedButton(
                child: new Text('Submit Referral'),
                onPressed: _submitData,
              ),

            ],

          )
      )
  ),

最佳答案

我能够重现您的问题，我不确定您为什么要以这种方式构建布局。您正在将 DropDownButton 作为 InputDecorator 的 child 属性，这很好。但是，它会引发此错误，因为 DropDownMenuItem 溢出了您的 InputDecorator。换句话说，您不仅在 InputDecorator 中包含 DopDownButton，而且您的 items 也试图包含在与出色地。因此，Flutter 对如何将 items 列表放置在 InputDecorator 提供的空间内感到困惑。

我真的很困惑你正在尝试构建什么样的布局，为什么你需要一个 Form 和一个 InputDecorator？

也许可以为您的设计选择提供一些背景信息，以便我们提供更好的帮助。

我已经使用 Row 和 TextField 小部件创建了一个更简单的布局，它可能会有帮助。

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String _mySelection;
  String _text = "Choose";
   List<Map> _myJson = [
    {"id": "ID 1310012", "name": "Newcommer"}, {"id": "ID 0000TEMP", "name": "Temp"}];

  Widget _children() {
    TextEditingController _controller = new TextEditingController(text: _text);
    return  new Expanded(child: new ListView(
            padding: const EdgeInsets.symmetric(horizontal: 16.0),
            children: <Widget>[
              new Container (
        child: new Row(
                  children: <Widget>[
                    new Expanded(
                      child: new TextField(
                        controller: _controller,
                      ),
                    ),
                    new DropdownButton(
                      isDense: true,
                      value: _mySelection,
                      items: _myJson.map((Map map) {
                        return new DropdownMenuItem<String>(
                          value: map["id"],
                          child: new Text(
                            map["name"],
                          ),
                        );
                      }).toList(),
                      onChanged: (String newValue) {
                        setState(() {
                          _mySelection = newValue;
                          _text = newValue;
                        });
                      })
              ],),),
              new RaisedButton(
                  child: new Text('Start'), onPressed: null),

            ]
        ));
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(title: new Text("Test")),
      body:  new Column(
        mainAxisSize: MainAxisSize.max,
        children: <Widget>[
           _children(),
        ],
      ),
    );
  }
}

关于Flutter RenderIndexedStack 对象在布局期间被赋予无限大小，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/46830812/