flutter - 没有为 Flutter 中的类 TagColumn 定义 Getter _text

Question

我在 Stack Overflow Flutter getter isn't specified for the class, when it is specified 上查看过这个问题.我仍然无法理解为什么我的类(class) 练习 无权访问变量 _文本 从 中的元素访问类型为 TagColumn 的列表.

class Practice extends StatefulWidget {
  @override
  _PracticeState createState() => _PracticeState();
}

class _PracticeState extends State<Practice>{
  int count  = 0;

  @override
  Widget build(BuildContext context){
    List<TagColumn> ok = List.generate(count, (int i) => new TagColumn());
    return Scaffold(
      backgroundColor: Colors.black,
      body: new LayoutBuilder(builder: (context, constraint){
      return new Stack(
        children: <Widget>[
          SingleChildScrollView(
            child: SafeArea(
              child: new Wrap(
                direction: Axis.horizontal,
                children: ok,
              )
            ),
          ),
          new Positioned(
            child: new Align(
              alignment: FractionalOffset.bottomRight,
              child: Container(
                margin: EdgeInsets.only(bottom: 50.0, right: 40.0),
                child: RawMaterialButton(
                  onPressed: (){
                    setState(() {
                      if(count != 0 && ok[count]._text.text.isEmpty){

                      }
                      else{
                          count +=1;
                      }
                    });
                  },
                  shape: CircleBorder(),
                  child: Icon(
                    Icons.add_circle,
                    size: 100.0,
                    color: Color(0xffd3d3d3),
                  ),
                )
              )
            )
          )

        ],
      );
      }),
    );
  }
}

class TagColumn extends StatefulWidget{
  @override
  State<StatefulWidget> createState() => new _TagColumn();
}

class _TagColumn extends State<TagColumn>{
  final _text = TextEditingController();
  bool _validate = false;

  @override

  Widget build(BuildContext context){
    final tagField = TextField(
      controller: _text,
      obscureText: false,
      style: TextStyle(fontFamily: 'Play', color: Colors.white, fontSize: 20),
      maxLines: null,
      keyboardType: TextInputType.text,
      decoration: InputDecoration(
        contentPadding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
        hintText: "Tag",
          errorText: _validate ? 'Value Can\'t be Empty': null,
          border:
          OutlineInputBorder(borderRadius: BorderRadius.circular(32.0))),
      );
    return Container(
      width: MediaQuery.of(context).size.width/2 - 40,
      margin: EdgeInsets.symmetric(horizontal: 20, vertical: 20),
      decoration: BoxDecoration(
        color: Colors.blue,
        borderRadius: BorderRadius.circular(32.0),
      ),
      child: Theme(
        data: ThemeData(
          hintColor: Colors.white,
        ),
        child: tagField,
      ),
    );
  }
}

如果用户没有在当前标签中输入文本，我想要做的是不允许用户在按下右下角的“加号”(见下图)时创建新标签。换句话说，如果它不为空。因此，我使用变量 final _text = TextEditingController() , 在按下加号按钮时检查当前标签是否为空。如果不是，则创建一个新标签。

Answer 1

dart 将以下划线开头的变量视为私有(private)变量(因为 dart 中没有 private 关键字)，因此为了解决您的问题，您需要删除文本变量之前的 _(下划线)。

这是怎么回事

1- 将 _text 变量移动到 TagColumn类 insted 的 State 类

class TagColumn extends StatefulWidget{
 final text = TextEditingController(); // removed the _ so that to access it inside the Practise class
  @override
  State<StatefulWidget> createState() => new _TagColumn();
}

并更新 TagColumn 类以反射(reflect)这些更改

class _TagColumn extends State<TagColumn>{
   // final _text = TextEditingController(); <---- since the text is now in the TagColumn class not the state class
  bool _validate = false;

  @override

  Widget build(BuildContext context){
    final tagField = TextField(
      controller: widget.text,
      obscureText: false,
      style: TextStyle(fontFamily: 'Play', color: Colors.white, fontSize: 20),
      maxLines: null,
      keyboardType: TextInputType.text,
      decoration: InputDecoration(
        contentPadding: EdgeInsets.fromLTRB(20.0, 15.0, 20.0, 15.0),
        hintText: "Tag",
          errorText: _validate ? 'Value Can\'t be Empty': null,
          border:
          OutlineInputBorder(borderRadius: BorderRadius.circular(32.0))),
      );
    return Container(
      width: MediaQuery.of(context).size.width/2 - 40,
      margin: EdgeInsets.symmetric(horizontal: 20, vertical: 20),
      decoration: BoxDecoration(
        color: Colors.blue,
        borderRadius: BorderRadius.circular(32.0),
      ),
      child: Theme(
        data: ThemeData(
          hintColor: Colors.white,
        ),
        child: tagField,
      ),
    );
  }
}