dart - 访问父类(super class)变量时出错

Question

我有以下 Dart 继承结构:

class MySuperList extends StatefulWidget {
  final category_name;
  MySuperList({this.category_name});
  @override
  _MySuperListState createState() => new _MySuperListState();
}

class _MySuperListState extends State<MySuperList> {

  Widget appBarTitle  = new Text(
      widget.category_name,   <== Only static members can be accessed in initializers
      style: new TextStyle(color: Colors.white);

如您所见，当我尝试使用 widget.category_name 访问父类(super class)中变量的值时，出现以下编译器错误:

Only static members can be accessed in initializers

我还能如何访问此值？

更新按照建议的答案进行操作后，文本现在卡在应用栏中。它确实会根据以下代码进行更改:

 Widget buildAppBar(BuildContext context) {
    return new AppBar(centerTitle: false, title: getAppBarTitle(), actions: <Widget>[
      new IconButton(
        icon: icon,
        onPressed: () {
          this.appBarTitle = null;
          setState(() {
            if (this.icon.icon == Icons.search) {
              this.icon = new Icon(
                Icons.close,
                color: Colors.white,
              );
                this.appBarTitle = new TextField(
                controller: _controller,
                autofocus: true,
                style: new TextStyle(
                  color: Colors.white,
                ),
                decoration: new InputDecoration(
                    prefixIcon: new Icon(Icons.search, color: Colors.white),
                    hintText: "Search...",
                    hintStyle: new TextStyle(color: Colors.white)),
                 onChanged: searchOperation,
              );                 
            } else {
              _handleSearchEnd();
            }
          });
        },
      ),
    ]);
  }

 void _handleSearchEnd() {
    setState(() {
      this.icon = new Icon(
        Icons.search,
        color: Colors.white,
      );

      _isSearching = false;
       this.appBarTitle = new Text(
        widget.category_name,
        style: new TextStyle(color: Colors.white),
      );
      _controller.clear();
    });
  }

如您所见，当单击搜索图标时，我将 appBarTitle 设置为 TextField。但是，不会生成文本字段。 appbar 仍然显示标题。我没有进行热重载或热重启。我实际上完全重启了。

Answer 1

这是你需要做的一个巧妙的方法

import 'package:flutter/material.dart';

class MySuperList extends StatefulWidget{
  final category_name;
  MySuperList({this.category_name});

  @override
  State<StatefulWidget> createState() {

    return _MySuperListState();
  }
}

class _MySuperListState extends State<MySuperList>{

  bool _isSearching=false;
  TextEditingController _controller = TextEditingController();

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: buildAppBar(),
    );
  }

  Widget buildAppBar(){
    return AppBar(
      centerTitle: false,
      title: getAppBarTitle(),
      actions: <Widget>[
        getAction()
      ],
    );
  }

  Widget getAction(){
    if(_isSearching){
      return IconButton(
        icon: Icon(
          Icons.close
        ),
        onPressed: (){
          setState(() {
            _controller.clear();
            _isSearching = false;
          });
        },
      );
    }else{
      return IconButton(
        icon: Icon(
            Icons.search
        ),
        onPressed: (){
          setState(() {
            _isSearching = true;
          });
        },
      );
    }
  }

  Widget getAppBarTitle(){
    if(_isSearching){
      return TextField(
        controller: _controller,
        autofocus: true,
        style: new TextStyle(
          color: Colors.white,
        ),
        decoration: new InputDecoration(
            prefixIcon: new Icon(Icons.search, color: Colors.white),
            hintText: "Search...",
            hintStyle: new TextStyle(color: Colors.white)),
        onChanged: searchOperation,
      );


    }else{
      return Text(
          widget.category_name,
          style: new TextStyle(color: Colors.white)
      );
    }
  }

  searchOperation(String value){
    //do what you need to onChanged
  }

}