dart - When I run flutter run, nothing shows up - Stack Overflow|江阴雨辰互联

I am Japanese and my English may be unnatural because I am using machine translation. I am a student and I am learning programming. I develop apps with Flutter.

When I build my app, nothing appears. At first I thought it was a problem with the source code, but when I ran the sample source code, the result did not change. Here is the source code and flutter doctor results. The emulator is Chrome. We will add any necessary information as soon as possible.

main.dart

// Copyright 2019 the Dart project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file.

import 'dart:math' as math;

import 'package:flutter/material.dart';

const int maxSeeds = 250;

void main() {
  runApp(const Sunflower());
}

class Sunflower extends StatefulWidget {
  const Sunflower({super.key});

  @override
  State<StatefulWidget> createState() {
    return _SunflowerState();
  }
}

class _SunflowerState extends State<Sunflower> {
  int seeds = maxSeeds ~/ 2;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        brightness: Brightness.dark,
        appBarTheme: const AppBarTheme(elevation: 2),
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Sunflower'),
        ),
        body: Center(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              Expanded(
                child: SunflowerWidget(seeds),
              ),
              const SizedBox(height: 20),
              Text('Showing ${seeds.round()} seeds'),
              SizedBox(
                width: 300,
                child: Slider(
                  min: 1,
                  max: maxSeeds.toDouble(),
                  value: seeds.toDouble(),
                  onChanged: (val) {
                    setState(() => seeds = val.round());
                  },
                ),
              ),
              const SizedBox(height: 20),
            ],
          ),
        ),
      ),
    );
  }
}

class SunflowerWidget extends StatelessWidget {
  static const tau = math.pi * 2;
  static const scaleFactor = 1 / 40;
  static const size = 600.0;
  static final phi = (math.sqrt(5) + 1) / 2;
  static final rng = math.Random();

  final int seeds;

  const SunflowerWidget(this.seeds, {super.key});

  @override
  Widget build(BuildContext context) {
    final seedWidgets = <Widget>[];

    for (var i = 0; i < seeds; i++) {
      final theta = i * tau / phi;
      final r = math.sqrt(i) * scaleFactor;

      seedWidgets.add(AnimatedAlign(
        key: ValueKey(i),
        duration: Duration(milliseconds: rng.nextInt(500) + 250),
        curve: Curves.easeInOut,
        alignment: Alignment(r * math.cos(theta), -1 * r * math.sin(theta)),
        child: const Dot(true),
      ));
    }

    for (var j = seeds; j < maxSeeds; j++) {
      final x = math.cos(tau * j / (maxSeeds - 1)) * 0.9;
      final y = math.sin(tau * j / (maxSeeds - 1)) * 0.9;

      seedWidgets.add(AnimatedAlign(
        key: ValueKey(j),
        duration: Duration(milliseconds: rng.nextInt(500) + 250),
        curve: Curves.easeInOut,
        alignment: Alignment(x, y),
        child: const Dot(false),
      ));
    }

    return FittedBox(
      fit: BoxFit.contain,
      child: SizedBox(
        height: size,
        width: size,
        child: Stack(children: seedWidgets),
      ),
    );
  }
}

class Dot extends StatelessWidget {
  static const size = 5.0;
  static const radius = 3.0;

  final bool lit;

  const Dot(this.lit, {super.key});

  @override
  Widget build(BuildContext context) {
    return DecoratedBox(
      decoration: BoxDecoration(
        color: lit ? Colors.orange : Colors.grey.shade700,
        borderRadius: BorderRadius.circular(radius),
      ),
      child: const SizedBox(
        height: size,
        width: size,
      ),
    );
  }
}

flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 3.24.3, on Microsoft Windows [Version 10.0.22631.4460], locale ja-JP)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
[√] Chrome - develop for the web
[√] Visual Studio - develop Windows apps (Visual Studio Professional 2022 17.10.5)
[√] Android Studio (version 2024.1)
[√] IntelliJ IDEA Community Edition (version 2024.2)
[√] VS Code (version 1.95.1)
[√] Connected device (3 available)
[!] Network resources
    X A network error occurred while checking "/": Semaphore timed out.

    X A network error occurred while checking "/": Semaphore timed out.

    X A network error occurred while checking "/": Semaphore timed out.

    X A network error occurred while checking "/": Semaphore timed out.

    X A network error occurred while checking "/": セSemaphore timed out.


! Doctor found issues in 1 category.

PS The Chrome window appears, but nothing is displayed.

I am Japanese and my English may be unnatural because I am using machine translation. I am a student and I am learning programming. I develop apps with Flutter.

main.dart

// Copyright 2019 the Dart project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file.

import 'dart:math' as math;

import 'package:flutter/material.dart';

const int maxSeeds = 250;

void main() {
  runApp(const Sunflower());
}

class Sunflower extends StatefulWidget {
  const Sunflower({super.key});

  @override
  State<StatefulWidget> createState() {
    return _SunflowerState();
  }
}

class _SunflowerState extends State<Sunflower> {
  int seeds = maxSeeds ~/ 2;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        brightness: Brightness.dark,
        appBarTheme: const AppBarTheme(elevation: 2),
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Sunflower'),
        ),
        body: Center(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              Expanded(
                child: SunflowerWidget(seeds),
              ),
              const SizedBox(height: 20),
              Text('Showing ${seeds.round()} seeds'),
              SizedBox(
                width: 300,
                child: Slider(
                  min: 1,
                  max: maxSeeds.toDouble(),
                  value: seeds.toDouble(),
                  onChanged: (val) {
                    setState(() => seeds = val.round());
                  },
                ),
              ),
              const SizedBox(height: 20),
            ],
          ),
        ),
      ),
    );
  }
}

class SunflowerWidget extends StatelessWidget {
  static const tau = math.pi * 2;
  static const scaleFactor = 1 / 40;
  static const size = 600.0;
  static final phi = (math.sqrt(5) + 1) / 2;
  static final rng = math.Random();

  final int seeds;

  const SunflowerWidget(this.seeds, {super.key});

  @override
  Widget build(BuildContext context) {
    final seedWidgets = <Widget>[];

    for (var i = 0; i < seeds; i++) {
      final theta = i * tau / phi;
      final r = math.sqrt(i) * scaleFactor;

      seedWidgets.add(AnimatedAlign(
        key: ValueKey(i),
        duration: Duration(milliseconds: rng.nextInt(500) + 250),
        curve: Curves.easeInOut,
        alignment: Alignment(r * math.cos(theta), -1 * r * math.sin(theta)),
        child: const Dot(true),
      ));
    }

    for (var j = seeds; j < maxSeeds; j++) {
      final x = math.cos(tau * j / (maxSeeds - 1)) * 0.9;
      final y = math.sin(tau * j / (maxSeeds - 1)) * 0.9;

      seedWidgets.add(AnimatedAlign(
        key: ValueKey(j),
        duration: Duration(milliseconds: rng.nextInt(500) + 250),
        curve: Curves.easeInOut,
        alignment: Alignment(x, y),
        child: const Dot(false),
      ));
    }

    return FittedBox(
      fit: BoxFit.contain,
      child: SizedBox(
        height: size,
        width: size,
        child: Stack(children: seedWidgets),
      ),
    );
  }
}

class Dot extends StatelessWidget {
  static const size = 5.0;
  static const radius = 3.0;

  final bool lit;

  const Dot(this.lit, {super.key});

  @override
  Widget build(BuildContext context) {
    return DecoratedBox(
      decoration: BoxDecoration(
        color: lit ? Colors.orange : Colors.grey.shade700,
        borderRadius: BorderRadius.circular(radius),
      ),
      child: const SizedBox(
        height: size,
        width: size,
      ),
    );
  }
}

flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 3.24.3, on Microsoft Windows [Version 10.0.22631.4460], locale ja-JP)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
[√] Chrome - develop for the web
[√] Visual Studio - develop Windows apps (Visual Studio Professional 2022 17.10.5)
[√] Android Studio (version 2024.1)
[√] IntelliJ IDEA Community Edition (version 2024.2)
[√] VS Code (version 1.95.1)
[√] Connected device (3 available)
[!] Network resources
    X A network error occurred while checking "https://pub.dev/": Semaphore timed out.

    X A network error occurred while checking "https://storage.googleapis/": Semaphore timed out.

    X A network error occurred while checking "https://maven.google/": Semaphore timed out.

    X A network error occurred while checking "https://cocoapods./": Semaphore timed out.

    X A network error occurred while checking "https://github/": セSemaphore timed out.


! Doctor found issues in 1 category.

PS The Chrome window appears, but nothing is displayed.

Share Improve this question edited Nov 18, 2024 at 13:00 asked Nov 18, 2024 at 12:46 para 112 bronze badges

Did you create a project and put everything in main.dart file(this will be inside the lib folder) and About the issue – Md. Yeasin Sheikh Commented Nov 18, 2024 at 12:50
Yes. I use flutter create – para Commented Nov 18, 2024 at 12:58
Did flutter counter app run on your machine(The default application that comes with flutter create projectName)? if so then Idk ;-, mean time you can try dartpad.dev – Md. Yeasin Sheikh Commented Nov 18, 2024 at 13:06
Sorry, I used flutter create testapp instead of flutter create. By the way, dartpad.dev worked fine. – para Commented Nov 18, 2024 at 13:11
I tried this. github/flutter/gallery/tree/main It worked fine. Why is that? – para Commented Nov 18, 2024 at 13:39

| Show 2 more comments

1 Answer 1

Sorted by: Reset to default 0

Did you tried a very simple test to start?

main.dart:

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Test',

      home: const Test(),
    );
  }
}

Test.dart:

class Test extends StatelessWidget {
  const Test({super.key});

  @override
  Widget build(BuildContext context) {
    return  Scaffold(
      body: Container(height: 200, width: 200, color: Colors.red),
    );
  }
}

Is a very simple example to test. Try to run on a Windows and Chrome. Do you are using Android Studio?

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dart - When I run flutter run, nothing shows up - Stack Overflow

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