在构建 StreamBuilder<UserData>(dirty, state: _StreamBuilderBaseState<UserData, AsyncSnapshot<UserData>>) 时引发了以下 NoSuchMethodError：答案

【问题标题】：The following NoSuchMethodError was thrown building StreamBuilder<UserData>(dirty, state: _StreamBuilderBaseState<UserData, AsyncSnapshot<UserData>>):在构建 StreamBuilder<UserData>(dirty, state: _StreamBuilderBaseState<UserData, AsyncSnapshot<UserData>>) 时引发了以下 NoSuchMethodError：
【发布时间】：2021-08-15 08:42:13
【问题描述】：

我正在尝试通过 Flutter 框架为带有 firebase 的应用程序构建用户设置菜单，但每当我尝试打开设置表单时，它都会告诉我之前分配给“name”的 name 属性现在设置为 null .

class SettingsFormTwo extends StatefulWidget {
  @override
  _SettingsFormState createState() => _SettingsFormState();
}

class _SettingsFormState extends State<SettingsFormTwo> {

  final _formKey = GlobalKey<FormState>();
  final List<String> sugars = ['0', '1', '2', '3', '4'];
  final List<int> strengths = [100, 200, 300, 400, 500, 600, 700, 800, 900];

  // form values
  String _currentName;
  String _currentSugars;
  int _currentStrength;

  @override
  Widget build(BuildContext context) {

    Player player = Provider.of<Player>(context);

    return StreamBuilder<UserData>(
        stream: DatabaseService(uid: player.uid).userData,
        builder: (context, snapshot) {
            UserData userData = snapshot.data;
            return Form(
              key: _formKey,
              child: Column(
                children: <Widget>[
                  const Text(
                    'Update your brew settings.',
                    style: TextStyle(fontSize: 18.0),
                  ),
                  SizedBox(height: 20.0),
                  TextFormField(
                    initialValue: userData.name, // This is where it says the error is at
                    decoration: textDecoration,
                    validator: (val) => val.isEmpty ? 'Please enter a name' : null,
                    onChanged: (val) => setState(() => _currentName = val),
                  ),
                ],
              ),
            );
          }
    );
  }
}

这是我收到的错误消息的 sn-p。

The following NoSuchMethodError was thrown building StreamBuilder<UserData>(dirty, state: _StreamBuilderBaseState<UserData, AsyncSnapshot<UserData>>#169ee):
The getter 'name' was called on null.
Receiver: null
Tried calling: name

【问题讨论】：

标签： firebase flutter dart

【解决方案1】：

您的 userData 为空，您应该更改

userData.name

到

userData?.name

【讨论】：