flutter - 不可为 null 的实例字段 ['controller' ] 必须在 flutter 中初始化

Question

美好的一天! 我是 Flutter 的新手，想开始我的 Startup，但我陷入了这个问题，以制作 Tabbar 为例......

因为这个问题我几乎郁闷了一整天......

Dart Analysis 在下面一直这样说......

非空实例字段['controller']必须在flutter中初始化

非常感谢提前。

        import 'package:flutter/material.dart';
import 'sub/firstPage.dart';
import 'sub/secondPage.dart';


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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(

        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);



  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {

  TabController controller;

  @override
  void initState() {
    super.initState();
    controller = TabController(length: 2, vsync: this);


  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('TabBar Example'),
        ),
        body: TabBarView(
          children: <Widget>[FirstApp(), SecondApp()],
          controller: controller,
        ),
        bottomNavigationBar: TabBar(tabs: [
          Tab(icon: Icon(Icons.looks_one, color: Colors.blue),),
          Tab(icon: Icon(Icons.looks_two, color: Colors.blue),),
        ],
        )
    );
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }


        }

Answer 1

请尝试一下，您错过了使用 Controller

import 'package:flutter/material.dart';
import 'sub/firstPage.dart';
import 'sub/secondPage.dart';


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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(

        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);



  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {

  late TabController controller;

  @override
  void initState() {
    super.initState();
    controller = TabController(length: 2, vsync: this);


  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('TabBar Example'),
        ),
        body: TabBarView(
          children: <Widget>[FirstApp(), SecondApp()],
          controller: controller,
        ),
        bottomNavigationBar: TabBar(
          controller: controller, // add here 
          tabs: [
          Tab(icon: Icon(Icons.looks_one, color: Colors.blue),),
          Tab(icon: Icon(Icons.looks_two, color: Colors.blue),),
        ],
        )
    );
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }


}