Flutter program was running before, no changes were made, it does't run anymore

Question

This is my code and the error I'm getting in Visual Studio Code. It used to work before, not sure if an update messed it up. I have other Flutter programs running just fine, not sure what the problem is with this one.

// 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],
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Launching lib/main.dart on Android SDK built for x86 in debug mode... ✓ Built build/app/outputs/apk/debug/app-debug.apk. Connecting to VM Service at ws://127.0.0.1:40605/I0TqLbk5jw4=/ws D/EGL_emulation( 7151): eglMakeCurrent: 0xe1b1a3c0: ver 2 0 (tinfo 0xe1b0f770) D/eglCodecCommon( 7151): setVertexArrayObject: set vao to 0 (0) 1 0 I/flutter ( 7151): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 7151): The following ArgumentError was thrown building MyApp(dirty, state: _MyAppState#202c3): I/flutter ( 7151): Invalid argument(s) I/flutter ( 7151): I/flutter ( 7151): The relevant error-causing widget was: I/flutter ( 7151): MyApp I/flutter ( 7151):
package:flutter_assignment/main.dart:11 I/flutter ( 7151): I/flutter ( 7151): When the exception was thrown, this was the stack: I/flutter ( 7151): #0 List.[] (dart:core-patch/array.dart:169:52) I/flutter ( 7151): #1 _MyAppState.build package:flutter_assignment/main.dart:57 I/flutter ( 7151): #2
StatefulElement.build package:flutter/…/widgets/framework.dart:4619 I/flutter ( 7151): #3 ComponentElement.performRebuild package:flutter/…/widgets/framework.dart:4502 I/flutter ( 7151): #4
StatefulElement.performRebuild package:flutter/…/widgets/framework.dart:4675 I/flutter ( 7151): #5
Element.rebuild package:flutter/…/widgets/framework.dart:4218 I/flutter ( 7151): #6 ComponentElement._firstBuild package:flutter/…/widgets/framework.dart:4481 I/flutter ( 7151): #7
StatefulElement._firstBuild package:flutter/…/widgets/framework.dart:4666 I/flutter ( 7151): #8
ComponentElement.mount package:flutter/…/widgets/framework.dart:4476 I/flutter ( 7151): #9 Element.inflateWidget package:flutter/…/widgets/framework.dart:3446 I/flutter ( 7151): #10
Element.updateChild package:flutter/…/widgets/framework.dart:3214 I/flutter ( 7151): #11 RenderObjectToWidgetElement._rebuild package:flutter/…/widgets/binding.dart:1148 I/flutter ( 7151): #12
RenderObjectToWidgetElement.mount package:flutter/…/widgets/binding.dart:1119 I/flutter ( 7151): #13
RenderObjectToWidgetAdapter.attachToRenderTree. package:flutter/…/widgets/binding.dart:1061 I/flutter ( 7151): #14
BuildOwner.buildScope package:flutter/…/widgets/framework.dart:2607 I/flutter ( 7151): #15
RenderObjectToWidgetAdapter.attachToRenderTree package:flutter/…/widgets/binding.dart:1060 I/flutter ( 7151): #16
WidgetsBinding.attachRootWidget package:flutter/…/widgets/binding.dart:941

chunhunghan chunhunghan · Accepted Answer · 2020-09-24T00:51:10

You can copy paste run full code below
You need to init _randomStringIndex
code snippet

var _randomStringIndex = 0;

working demo

full code

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],
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Flutter program was running before, no changes were made, it does't run anymore

2 Answers