未设置Flutter setState

Question

我有一个用于创建侧边栏菜单的小部件：

Widget dashboard(context) {
  return Material(
    elevation: 8,
    color: backgroundColor,
    child: Container(
      padding: const EdgeInsets.only(left: 16, right: 16, top: 48),
      child: Column(
        children: <Widget>[
          Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              mainAxisSize: MainAxisSize.max,
              children: [
            InkWell(child: Icon(Icons.menu, color: Colors.white), onTap: () {
              setState(() {
                isCollapsed = !isCollapsed;
              });
            },),
            Text("Corona App", style: TextStyle(fontSize: 24.0, color: Colors.white)),
                Icon(Icons.settings, color: Colors.white),
          ])
        ],
      ),
    )
  );
}

但是我不断收到未定义setState函数的错误。我的主要应用是statefullwidget，所以这很奇怪。谁能帮我吗？

这里是完整代码！

import 'package:flutter/material.dart';

final Color backgroundColor = Color(0xFF4A4A58);

class MenuDashboard extends StatefulWidget {
  @override
  _MenuDashboardState createState() => _MenuDashboardState();
}

class _MenuDashboardState extends State<MenuDashboard> {

  bool isCollapsed = true;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: backgroundColor,
      body: Stack(
        children: <Widget>[
          menu(context),
          dashboard(context),
        ],
      ),
    );
  }
}

Widget menu(context) {
  return Padding(
    padding: const EdgeInsets.only(left: 16.0),
    child: Align(
      alignment: Alignment.centerLeft,
    child: Column(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.spaceAround,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
      Text("Home", style: TextStyle(color: Colors.white, fontSize: 20),),
      SizedBox(height: 10.0),
      Text("Brochures", style: TextStyle(color: Colors.white, fontSize: 20),),
        SizedBox(height: 10.0),
      Text("Visitekaartje", style: TextStyle(color: Colors.white, fontSize: 20),),
        SizedBox(height: 10.0),
      ]
     )
    )
  );
}

Widget dashboard(context) {
  return Material(
    elevation: 8,
    color: backgroundColor,
    child: Container(
      padding: const EdgeInsets.only(left: 16, right: 16, top: 48),
      child: Column(
        children: <Widget>[
          Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              mainAxisSize: MainAxisSize.max,
              children: [
            InkWell(child: Icon(Icons.menu, color: Colors.white), onTap: () {
              setState(() {
                isCollapsed = !isCollapsed;
              });
            },),
            Text("Corona App", style: TextStyle(fontSize: 24.0, color: Colors.white)),
                Icon(Icons.settings, color: Colors.white),
          ])
        ],
      ),
    )
  );
}

带有错误消息：'未定义功能setState'

Answer 1

setState是State类的成员，这意味着它只能在扩展State的StatefulWidget类的类内部调用。如果您的类正在扩展StatelessWidget，则不能调用超类提供的状态成员/方法，包括setState，initState和dispose方法。

Answer 2

setState仅可在StatefulWidget内部调用。因此，如果我做对了，请在setState小部件中使用Widget dashboard or menu。这是行不通的，因为这些小部件在类之外。尝试将widgets放在类中