颤振程序以前运行过，没有进行任何更改，它不再运行

Question

这是我的代码和我在Visual代码中遇到的错误。它以前经常工作，不确定更新是否弄糟了它。我还有其他的颤振程序运行得很好，不知道这个程序有什么问题。

// 1) Create a new Flutter App (in this project) and output an AppBar and some text
// below it
// 2) Add a button which changes the text (to any other text of your choice)
// 3) Split the app into three widgets: App, TextControl & Text

import 'dart:math';

import 'package:flutter/material.dart';

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

// void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  Random _stringIndex = new Random();
  var _randomStringIndex;

  final _strings = const [
    "Hello",
    "This is a string",
    "This is random",
  ];

  void _changeText() {
    setState(() {
      _randomStringIndex = _stringIndex.nextInt(_strings.length);
    });

    print(_strings[_randomStringIndex]);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My First App'),
        ),
        body: Center(
          child: Container(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                RaisedButton(
                  onPressed: _changeText,
                ),
                Text(
                  _strings[_randomStringIndex],
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

在Android上启动lib/main.DAT在调试模式下为x86构建.✓构建了build/app/outputs/apk/debug/app-调试器。连接到VM服务的位置为ws://127.0.0.1:40605/I0TqLbk5jw4=/ws D/EGL_ to ( 7151)：eglMakeCurrent: 0xe1b1a3c0: ver2.0 (tinfo 0xe1b0f770) D/eglCodecCommon7151: setVertexArrayObject:将vao设置为0 (0) 1.0 I/flutter ( 7151)：由小部件库╞═══════════════════════════════════════════捕获的══╡异常ArgumentError I/════════════════( 7151)：抛出以下════════════════构建MyApp(脏，状态：_MyAppState#202c3)：I/颤振( 7151)：无效的参数I/颤振( 7151)：I/颤振( 7151)：相关的导致错误的小部件是:I/颤振( 7151)：MyApp I/颤振( 7151)：

程序包：_MyAppState.build _assignment/main.dart:11I/_MyAppState.build( 7151)：I/flutter ( 7151)：当抛出异常时，这是堆栈:i/颤振( 7151)：#0列表。

StatefulElement.build包:颤振/…/widgets/Frawork.DART:4619 I/flutter ( 7151)：#3 ComponentElement.performRebuild包:flutter/…/widget/Frawork.DAT:4502 I/颤振( 7151)：#4

StatefulElement.performRebuild包:颤振/…/widget/Frawork.DAT:4675 I/颤振( 7151)：#5

Element.rebuild包:颤振/…/widgets/Frawork.DART:4218 I/flutter ( 7151)：#6 ComponentElement._firstBuild包:flutter/…/widget/Frawork.DAT:4481 I/颤振( 7151)：#7

StatefulElement._firstBuild包:颤振/…/widget/Frawork.DART:4666 I/颤振( 7151)：#8

ComponentElement.mount包:颤振/…/widgets/Frawork.DART:4476I/flutter( 7151)：#9 Element.inflateWidget包:flutter/…/widget/Frawork.DAT:3446 I/颤振( 7151)：#10

Element.updateChild包:颤振/…/widgets/Frawork.DART:3214 I/flutter ( 7151)：#11 RenderObjectToWidgetElement._rebuild包:flutter/…/widget/binding.dart:1148 I/颤振( 7151)：#12

RenderObjectToWidgetElement.mount包:颤振/…/widget/binding.dart:1119 I/颤振( 7151)：#13

RenderObjectToWidgetAdapter.attachToRenderTree.包装:颤振/…/widget/binding.dart:1061 I/颤振( 7151)：#14

BuildOwner.buildScope包:颤振/…/widget/Frawork.DAT:2607 I/颤振( 7151)：#15

RenderObjectToWidgetAdapter.attachToRenderTree包:颤振/…/widget/binding.dart:1060 I/颤振( 7151)：#16

WidgetsBinding.attachRootWidget包:颤振/…/widget/binding.dart:941

Answer 1

您可以复制粘贴，运行下面的完整代码

您需要插入_randomStringIndex

代码段

var _randomStringIndex = 0;

工作演示

​

​

全码

import 'dart:math';

import 'package:flutter/material.dart';

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

// void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  Random _stringIndex = new Random();
  var _randomStringIndex = 0;

  final _strings = const [
    "Hello",
    "This is a string",
    "This is random",
  ];

  void _changeText() {
    setState(() {
      _randomStringIndex = _stringIndex.nextInt(_strings.length);
    });

    print(_strings[_randomStringIndex]);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My First App'),
        ),
        body: Center(
          child: Container(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                RaisedButton(
                  onPressed: _changeText,
                ),
                Text(
                  _strings[_randomStringIndex],
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Answer 2

尝试在项目(终端)中运行此命令：

flutter clean

然后再运行一次！