Flutter使用Navigator跳转时报Undefined name 'context'错误如何解决

• context是StatelessWidget/StatefulWidget的build方法的入参，仅能在build方法内部的作用域中访问。当前list1/list2/list3被定义为类的全局属性，不在build的作用域范围内，所以无法读取到context变量，触发未定义报错。
• 额外语法问题：部分Navigator.push代码结尾多写了多余的闭合括号，也会触发编译报错。

第一步：调整列表的定义位置 #

把list1/list2/list3三个列表的定义，从类的属性位置挪到build方法内部，放在return语句之前即可，这样就能正常访问到build方法传入的context变量。

第二步：修正多余的语法符号 #

删除所有Navigator.push代码段里多余的闭合括号。

（可选）代码规范优化 #

Flutter官方要求类名使用大驼峰命名，建议把chooseCategory类名改为ChooseCategory，避免后续潜在的规范类报错。

import 'package:flutter/material.dart';
import 'package:origitive_app/main.dart';
import 'package:origitive_app/Productpage.dart';

void main() {
  runApp(ChooseCategory());
}

class ChooseCategory extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // 三个列表挪到build方法内部定义
    List<Widget> list1 = <Widget>[
      ListTile(
        title: Text('Shoes',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/men1.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Clothing',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        subtitle: Text('429 Castro St'),
        leading: Image.asset("assets/Images/men2.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Accessories',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/men3.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
    ];

    List<Widget> list2 = <Widget>[
      ListTile(
        title: Text('Shoes',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        subtitle: Text('85 W Portal Ave'),
        leading: Image.asset("assets/Images/women1.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Clothing',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/women2.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Accessories',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/women3.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
    ];

    List<Widget> list3 = <Widget>[
      ListTile(
        title: Text('Boys Shoes',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/boy1.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Girls Shoes',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/girl1.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Boys Clothing',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/boy1.png"),
        trailing: Icon(Icons.arrow_forward),
        onTap: () {
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
      ),
      ListTile(
        title: Text('Girls Clothing',
            style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0)),
        leading: Image.asset("assets/Images/girl2.png"),
        onTap: (){
          Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => Productpage()));
        },
        trailing: Icon(Icons.arrow_forward),
      ),
    ];

    return MaterialApp(
        debugShowCheckedModeBanner: false,
        home: DefaultTabController(
          length: 3,
          child: Scaffold(
            appBar: AppBar(
              title: const Text('Collections'),
              backgroundColor: Colors.grey[400],
              actions: [
                PopupMenuButton(
                  icon: Icon(Icons.menu),
                  color: Colors.blue,
                  itemBuilder: (context) =>
                  [
                    PopupMenuItem<int>(
                      value: 0,
                      child: Text(
                        "Home", style: TextStyle(color: Colors.white),),
                    ),
                    PopupMenuItem<int>(
                      value: 1,
                      child: Text(
                        "About", style: TextStyle(color: Colors.white),),
                    ),
                    PopupMenuItem<int>(
                      value: 2,
                      child: Text(
                        "Settings", style: TextStyle(color: Colors.white),),
                    ),
                  ],
                  onSelected: (item) => {print(item)},
                ),
              ],
              bottom: TabBar(isScrollable: true, tabs: [
                Tab(text: 'MEN',),
                Tab(text: 'WOMEN',),
                Tab(text: 'KIDS',),
              ]),
            ),
            body: TabBarView(
              children: [
                ListView(
                  children: list1,
                ),
                ListView(
                  children: list2,
                ),
                ListView(
                  children: list3,
                ),
              ],
            ),
            bottomNavigationBar: BottomNavigationBar(
              type: BottomNavigationBarType.fixed,
              items: const <BottomNavigationBarItem>[
                BottomNavigationBarItem(
                  icon: Icon(Icons.home),
                  label: Text('Home').data,
                ),
                BottomNavigationBarItem(
                  icon: Icon(Icons.business),
                  label: Text('Business').data,
                ),
                BottomNavigationBarItem(
                  icon: Icon(Icons.computer),
                  label: Text('Technology').data,
                ),
                BottomNavigationBarItem(
                  icon: Icon(Icons.book),
                  label: Text('Education').data,
                ),
              ],
            ),
          ),
        ));
  }
}

内容的提问来源于stack exchange，提问作者Rashmi Gunawardana