Flutter默认Demo可运行Web，无法在模拟器及真机启动，求解决方案

我正在Udemy平台的《Flutter & Dart 开发iOS和Android应用》课程学习，已完成大部分配置。默认Demo代码可编译并正常运行Web端（），但在VS Code和Android Studio中均无法在模拟器及真机上启动。

编译错误日志 #

Exception in thread "main" java.net.SocketException: A connection attempt failed because the connected party did not properly respond after some time, or established connection failed because the connected host has failed to respond
    at java.base/sun.nio.ch.NioSocketImpl.implRead(NioSocketImpl.java:325)
    at java.base/sun.nio.ch.NioSocketImpl.read(NioSocketImpl.java:350)
    at java.base/sun.nio.ch.NioSocketImpl$1.read(NioSocketImpl.java:803)
    at java.base/java.net.Socket$SocketInputStream.read(Socket.java:966)
    at java.base/sun.security.ssl.SSLSocketInputRecord.read(SSLSocketInputRecord.java:484)
    at java.base/sun.security.ssl.SSLSocketInputRecord.readHeader(SSLSocketInputRecord.java:478)
    at java.base/sun.security.ssl.SSLSocketInputRecord.decode(SSLSocketInputRecord.java:160)
    at java.base/sun.security.ssl.SSLTransport.decode(SSLTransport.java:111)
    at java.base/sun.security.ssl.SSLSocketImpl.decode(SSLSocketImpl.java:1510)
    at java.base/sun.security.ssl.SSLSocketImpl.readHandshakeRecord(SSLSocketImpl.java:1425)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:455)
    at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:426)
    at java.base/sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:580)
    at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:187)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.followRedirect0(HttpURLConnection.java:2902)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.followRedirect(HttpURLConnection.java:2811)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1927)
    at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1589)
    at java.base/sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:224)
    at org.gradle.wrapper.Download.downloadInternal(Download.java:58)
    at org.gradle.wrapper.Download.download(Download.java:44)
    at org.gradle.wrapper.Install$1.call(Install.java:61)
    at org.gradle.wrapper.Install$1.call(Install.java:48)
    at org.gradle.wrapper.ExclusiveFileAccessManager.access(ExclusiveFileAccessManager.java:65)
    at org.gradle.wrapper.Install.createDist(Install.java:48)
    at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:128)
    at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:61)
Exception: Gradle task assembleDebug failed with exit code 1
Exited (sigterm)

已尝试的解决方法 #

• 安装JDK
• 参考Stack Overflow相关解决方案
• 执行flutter --v、flutter clean、flutter run命令

项目代码（main.dart） #

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter - The Complete Guide',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

解决方案 #

从错误日志看，核心问题是Gradle下载依赖时网络连接超时，以下是针对性解决方法：

1. 配置Gradle国内镜像 #

修改项目根目录android/build.gradle中的repositories部分，替换为国内镜像：

buildscript {
    ext.kotlin_version = '1.7.10'
    repositories {
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/nexus/content/groups/public' }
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:7.3.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/nexus/content/groups/public' }
    }
}

2. 手动下载Gradle并配置 #

• 查看android/gradle/wrapper/gradle-wrapper.properties中的Gradle版本（如distributionUrl=https\://services.gradle.org/distributions/gradle-7.5-all.zip）
• 手动下载对应版本的Gradle压缩包
• 解压到本地路径（如C:\gradle\gradle-7.5或~/gradle/gradle-7.5）
• 修改gradle-wrapper.properties中的distributionUrl为本地路径：

  distributionUrl=file\:///C:/gradle/gradle-7.5-all.zip
  

  注意Windows路径需用\转义，Mac/Linux直接用/

3. 检查网络代理设置 #

• 关闭全局代理或VPN，确保Gradle能正常访问网络
• 若需代理，在项目根目录创建gradle.properties文件，添加代理配置：

  systemProp.http.proxyHost=你的代理IP
  systemProp.http.proxyPort=代理端口
  systemProp.https.proxyHost=你的代理IP
  systemProp.https.proxyPort=代理端口
  

4. 清除Gradle缓存并重建 #

执行以下命令：

flutter clean
cd android
./gradlew clean
./gradlew build --refresh-dependencies
cd ..
flutter run

5. 检查JDK版本 #

确保使用Flutter推荐的JDK版本（如OpenJDK 11），避免版本不兼容问题。

内容的提问来源于stack exchange，提问作者Chinez