关于flutter:Flutter-命令本质之-Flutter-tools-机制源码深入分析

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Flutter 系列文章连载～

  • 《Flutter Android 工程构造及应用层编译源码深入分析》
  • 《Flutter 命令实质之 Flutter tools 机制源码深入分析》
  • 《Flutter 的 runApp 与三棵树诞生流程源码剖析》
  • 《Flutter Android 端 Activity/Fragment 流程源码剖析》
  • 《Flutter Android 端 FlutterInjector 及依赖流程源码剖析》
  • 《Flutter Android 端 FlutterEngine Java 相干流程源码剖析》
  • 《Flutter Android 端 FlutterView 相干流程源码剖析》
  • 《Flutter 绘制动机 VSYNC 流程源码全方位剖析》
  • 《Flutter 安卓 Platform 与 Dart 端音讯通信形式 Channel 源码解析》

背景

上一篇《Flutter Android 工程构造及应用层编译源码深入分析》咱们剖析了 Flutter Android 相干的应用层次要编译流程，其中剖析到底层实质命令工具【Flutter SDK 下 bin/flutter 编译命令剖析】大节时只提到，咱们执行任何 flutter 命令的实质都是把参数传递到了 FLUTTER_SDK_DIR/packages/flutter_tools/bin/flutter_tools.dart 源码的 main 办法中，没有对这外面进行深入分析。本文要做的事就是层层递进揭开这里的实质，并与上篇响应解释编译产物的由来。

flutter_tools 介绍

通过 flutter -h 命令咱们能够直观全局感触都反对哪些参数，有些参数还有子参数。咱们所执行的所有参数实质都走进了上面模块的源码入口中。

因而咱们如果间接想从源码形式应用 flutter tools，则能够间接当前目录中如下命令：

# ARGS 就是一堆参数，譬如咱们上篇的 build apk
dart bin/flutter_tools.dart ARGS

如果想从新生成 Flutter Tools snapshot，能够间接当前目录中执行如下命令：

rm ../../bin/cache/flutter_tools.stamp ../../bin/cache/flutter_tools.snapshot

这样就胜利删除了上篇中 shell 脚本调用的 Flutter Tools snapshot，而后在执行时会主动从新生成一个。

源码剖析

下面既然交代了整个背景，那么咱们接下来就基于 Flutter SDK 入口 packages/flutter_tools/bin/flutter_tools.dart 开始剖析，整个剖析持续承接上篇 flutter build apk 命令，如下：

//1、导入 packages/flutter_tools/lib/executable.dart 文件
import 'package:flutter_tools/executable.dart' as executable;
//2、入口重点，执行 executable.main 办法，并将咱们 `build apk` 参数传入
void main(List<String> args) {executable.main(args);
}

接下来咱们去 packages/flutter_tools/lib/executable.dart 看看他的 main 办法，如下：

Future<void> main(List<String> args) async {
  // 一堆参数解析判断啥的，譬如解析 flutter doctor 的 doctor 参数啥的
  ......
  //1、重点！runner 的实质是 import 'runner.dart' as runner;
  // 实质就是调用 run 办法的各种参数传递，重点关注第一个和第二个参数即可
  await runner.run(
    args,
    () => generateCommands(
      verboseHelp: verboseHelp,
      verbose: verbose,
    ),
    ......,
  );
}
//2、步骤 1 中 runner.run 的第二个外围参数办法定义
//FlutterCommand 为 packages/flutter_tools/lib/src/runner/flutter_command.dart 中定义的抽象类
// 这个办法实质就是把 flutter 执行的命令参数列表全副退出列表，相似命令模式
List<FlutterCommand> generateCommands({
  @required bool verboseHelp,
  @required bool verbose,
}) => <FlutterCommand>[
  AnalyzeCommand(......),
  AssembleCommand(verboseHelp: verboseHelp, buildSystem: globals.buildSystem),
  AttachCommand(verboseHelp: verboseHelp),
  BuildCommand(verboseHelp: verboseHelp),
  ChannelCommand(verboseHelp: verboseHelp),
  CleanCommand(verbose: verbose),
  ConfigCommand(verboseHelp: verboseHelp),
  CreateCommand(verboseHelp: verboseHelp),
  DaemonCommand(hidden: !verboseHelp),
  DevicesCommand(verboseHelp: verboseHelp),
  DoctorCommand(verbose: verbose),
  DowngradeCommand(verboseHelp: verboseHelp),
  DriveCommand(verboseHelp: verboseHelp,
    ......
  ),
  EmulatorsCommand(),
  FormatCommand(),
  GenerateCommand(),
  GenerateLocalizationsCommand(......),
  InstallCommand(),
  LogsCommand(),
  MakeHostAppEditableCommand(),
  PackagesCommand(),
  PrecacheCommand(......),
  RunCommand(verboseHelp: verboseHelp),
  ScreenshotCommand(),
  ShellCompletionCommand(),
  TestCommand(verboseHelp: verboseHelp),
  UpgradeCommand(verboseHelp: verboseHelp),
  SymbolizeCommand(......),
  // Development-only commands. These are always hidden,
  IdeConfigCommand(),
  UpdatePackagesCommand(),];
......

让咱们把眼光先挪动到 runner.dart 文件的 run 办法，而后回过头来看下面代码中的步骤 1 如何调用步骤 2，如下：

Future<int> run(
  List<String> args,
  List<FlutterCommand> Function() commands, {
    bool muteCommandLogging = false,
    bool verbose = false,
    bool verboseHelp = false,
    bool reportCrashes,
    String flutterVersion,
    Map<Type, Generator> overrides,
  }) async {
  ......
  //1、FlutterCommandRunner 位于 packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
  return runInContext<int>(() async {
    reportCrashes ??= !await globals.isRunningOnBot;
    //2、创立 runner 对象实例，并把上一片段代码中步骤 2 办法返回的 FlutterCommand 列表追加进 runner 中
    final FlutterCommandRunner runner = FlutterCommandRunner(verboseHelp: verboseHelp);
    commands().forEach(runner.addCommand);
    ......
    return runZoned<Future<int>>(() async {
      try {
          //3、根据 args 参数执行 runner 实例的 run 办法
        await runner.run(args);
        ......
      } catch (error, stackTrace) {  // ignore: avoid_catches_without_on_clauses
        ......
      }
    }, onError: (Object error, StackTrace stackTrace) async { // ignore: deprecated_member_use
      ......
    });
  }, overrides: overrides);
}

能够看到，首先实例化了一个 FlutterCommandRunner 对象，接着把所有反对的 FlutterCommand 列表退出 runner 对象中，而后调用了 runner 的 run 办法，所以咱们当初查看 packages/flutter_tools/lib/src/runner/flutter_command_runner.dart 文件的 run 办法，如下：

......
@override
Future<void> run(Iterable<String> args) {
  ......
  // 实质调用了父类 CommandRunner 的 run 办法，run 办法调用了子类 FlutterCommandRunner 的 runCommand 办法
  // 子类 FlutterCommandRunner 的 runCommand 最终又调用了父类 CommandRunner 的 runCommand 办法
  return super.run(args);
}
......

所以咱们接下来看父类 CommandRunner 的 runCommand 办法，如下：

  Future<T?> runCommand(ArgResults topLevelResults) async {
      //1、flutter 命令前面传递进来参数，譬如 build apk
    var argResults = topLevelResults;
    //2、后面剖析过的，runner 中增加的反对命令列表
    var commands = _commands;
    //3、定义一个 Command 变量，用来最终根据参数赋值为对应的 Command 对象实例
    Command? command;
    var commandString = executableName;
    //4、while 条件为真，因为 commands 为反对的参数列表
    while (commands.isNotEmpty) {
      ......
      //5、填充指令
      argResults = argResults.command!;
      command = commands[argResults.name]!;
      command._globalResults = topLevelResults;
      command._argResults = argResults;
      commands = command._subcommands as Map<String, Command<T>>;
      commandString += '${argResults.name}';
      ......
    }
    ......
    //6、执行对应命令的 run 办法
    return (await command.run()) as T?;
  }
  ......
}

能够看到，这就是一个规范的命令模式设计，先把反对的命令增加到列表，而后根据参数遍历匹配对应命令进行执行。上面咱们以 flutter build apk 命令为例来看其对应的 BuildCommand 命令（packages/flutter_tools/lib/src/commands/build.dart）实现，如下：

class BuildCommand extends FlutterCommand {BuildCommand({ bool verboseHelp = false}) {addSubcommand(BuildAarCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildApkCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildAppBundleCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildIOSCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildIOSFrameworkCommand(
      buildSystem: globals.buildSystem,
      verboseHelp: verboseHelp,
    ));
    addSubcommand(BuildIOSArchiveCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildBundleCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildWebCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildMacosCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildLinuxCommand(
      operatingSystemUtils: globals.os,
      verboseHelp: verboseHelp
    ));
    addSubcommand(BuildWindowsCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildWindowsUwpCommand(verboseHelp: verboseHelp));
    addSubcommand(BuildFuchsiaCommand(verboseHelp: verboseHelp));
  }
  // 上一小段代码中 command = commands[argResults.name]就是这么失去的
  //name=build 就是执行 flutter build apk 中的 build 字符串
  @override
  final String name = 'build';

  @override
  final String description = 'Build an executable app or install bundle.';

  @override
  Future<FlutterCommandResult> runCommand() async => null;}

能够看到，任意一个命令根本都继承自 FlutterCommand 实现，命令的执行都是调用了 FlutterCommand 的 run 办法，如下：

abstract class FlutterCommand extends Command<void> {
  ......
  //runner 对象中最终执行调用的办法是这个
  @override
  Future<void> run() {
    ......
    return context.run<void>(
      name: 'command',
      overrides: <Type, Generator>{FlutterCommand: () => this},
      body: () async {
        ......
        try {
          // 见名知意，先校验再运行命令
          commandResult = await verifyThenRunCommand(commandPath);
        } finally {......}
      },
    );
  }
  ......
    @mustCallSuper
  Future<FlutterCommandResult> verifyThenRunCommand(String commandPath) async {
    //1、如果须要更新缓存就先更新缓存
    if (shouldUpdateCache) {await globals.cache.updateAll(<DevelopmentArtifact>{DevelopmentArtifact.universal});
      await globals.cache.updateAll(await requiredArtifacts);
    }
    globals.cache.releaseLock();
    //2、校验命令
    await validateCommand();
    //3、如果须要先执行 pub 就先执行，譬如 pub get 下载依赖
    if (shouldRunPub) {
      ......
      //4、执行 pub get 下载依赖，即下载 pubspec.yaml 里配置的依赖
      await pub.get(context: PubContext.getVerifyContext(name),
        generateSyntheticPackage: project.manifest.generateSyntheticPackage,
        checkUpToDate: cachePubGet,
      );
      await project.regeneratePlatformSpecificTooling();
      if (reportNullSafety) {await _sendNullSafetyAnalyticsEvents(project);
      }
    }

    setupApplicationPackages();
    ......
    //5、真正开始执行命令
    return runCommand();}
}

绕一圈最终咱们又回到 BuildCommand 类，能够发现其 runCommand 办法重写为空实现，而其结构时通过 addSubcommand 办法追加了很多子命令，譬如执行 flutter build aar 编译 aar 的 BuildAarCommand 命令、执行 flutter build apk 编译 apk 的 BuildApkCommand 命令。整个 sub command 与其宿主又算是一个责任链，所以下面同样的套路程序对于 sub command 同样实用，因而咱们去看下编译 apk 产物的 BuildApkCommand 源码（packages/flutter_tools/lib/src/commands/build_apk.dart），如下：

class BuildApkCommand extends BuildSubCommand {BuildApkCommand({bool verboseHelp = false}) {
    ......
    // 一堆参数的确认
  }
  // 对应 flutter build apk 外面子命令字符串 apk
  @override
  final String name = 'apk';
  ......
  // 实质命令执行办法
  @override
  Future<FlutterCommandResult> runCommand() async {
    ......
    // 调用 androidBuilder 的 buildApk 办法进行真正的编译，目测外面的产物也就是上一篇文章剖析的那些
    //androidBuilder 位于 packages/flutter_tools/lib/src/android/android_builder.dart
    await androidBuilder.buildApk(project: FlutterProject.current(),
      target: targetFile,
      androidBuildInfo: androidBuildInfo,
    );
    return FlutterCommandResult.success();}
}

顺着这条路咱们持续跟进位于 packages/flutter_tools/lib/src/android/android_builder.dart 的 androidBuilder 属性的 buildApk 办法，如下：

// 实质是 packages/flutter_tools/lib/src/context_runner.dart 中 context.run 办法中的 AndroidGradleBuilder 实例
AndroidBuilder get androidBuilder {return context.get<AndroidBuilder>();
}
// 抽象类定义，AndroidBuilder
abstract class AndroidBuilder {const AndroidBuilder();
  // 定义编译 aar 的办法
  Future<void> buildAar({
    @required FlutterProject project,
    @required Set<AndroidBuildInfo> androidBuildInfo,
    @required String target,
    @required String outputDirectoryPath,
    @required String buildNumber,
  });

  // 定义编译 apk 的办法
  Future<void> buildApk({
    @required FlutterProject project,
    @required AndroidBuildInfo androidBuildInfo,
    @required String target,
  });

  // 定义编译 aab 的办法
  Future<void> buildAab({
    @required FlutterProject project,
    @required AndroidBuildInfo androidBuildInfo,
    @required String target,
    bool validateDeferredComponents = true,
    bool deferredComponentsEnabled = false,
  });
}

所以咱们持续去看 AndroidGradleBuilder 实现类（packages/flutter_tools/lib/src/android/gradle.dart）的 buildApk 办法，如下：

class AndroidGradleBuilder implements AndroidBuilder {
  AndroidGradleBuilder({......}) : ......;
  ......
  //1、编译 apk 的办法
  @override
  Future<void> buildApk({
    @required FlutterProject project,
    @required AndroidBuildInfo androidBuildInfo,
    @required String target,
  }) async {
      //2、调用
    await buildGradleApp(
      project: project,
      androidBuildInfo: androidBuildInfo,
      target: target,
      isBuildingBundle: false,
      localGradleErrors: gradleErrors,
    );
  }
  ......
  //3、真的编译
  Future<void> buildGradleApp({@required FlutterProject project, //FlutterProject.current()
    @required AndroidBuildInfo androidBuildInfo, //build configuration
    @required String target, //dart 代码入口，缺省 lib/main.dart
    @required bool isBuildingBundle, // 是 aab 还是 apk，默认 false 则 apk
    @required List<GradleHandledError> localGradleErrors,
    bool shouldBuildPluginAsAar = false, // 是不是将插件编译为 aar
    bool validateDeferredComponents = true,
    bool deferredComponentsEnabled = false,
    int retries = 1,
  }) async {
    //4、查看反对的 android 版本，获取 android 编译产物目录，即 gradle 中配置的 build 产物目录，默认为我的项目根目录下的 build 目录
    if (!project.android.isSupportedVersion) {_exitWithUnsupportedProjectMessage(_usage, _logger.terminal);
    }
    final Directory buildDirectory = project.android.buildDirectory;
    //5、读取安卓相干属性文件判断是否应用 androidx，而后发送编译事件参数
    final bool usesAndroidX = isAppUsingAndroidX(project.android.hostAppGradleRoot);
    if (usesAndroidX) {BuildEvent('app-using-android-x', flutterUsage: _usage).send();} else if (!usesAndroidX) {BuildEvent('app-not-using-android-x', flutterUsage: _usage).send();
      ......
    }
    //6、更新安卓我的项目中 local.properties 中的 versionName 和 versionCode 值，值来自于 public.yaml 文件配置
    updateLocalProperties(project: project, buildInfo: androidBuildInfo.buildInfo);
    //7、编译 aar 的话就走 buildPluginsAsAar 办法进行
    if (shouldBuildPluginAsAar) {
      // Create a settings.gradle that doesn't import the plugins as subprojects.
      createSettingsAarGradle(project.android.hostAppGradleRoot, _logger);
      await buildPluginsAsAar(
        project,
        androidBuildInfo,
        buildDirectory: buildDirectory.childDirectory('app'),
      );
    }
    //8、获取编译 apk 或者 aab 对应的规范安卓 task name，构建参数等信息，也就是 gradle 命令前面一堆的参数结构
    final BuildInfo buildInfo = androidBuildInfo.buildInfo;
    final String assembleTask = isBuildingBundle
        ? getBundleTaskFor(buildInfo)
        : getAssembleTaskFor(buildInfo);
    ......
    final List<String> command = <String>[_gradleUtils.getExecutable(project),
    ];
    ......
    //9、根据条件追加 command 的一堆参数，譬如 -Psplit-per-abi=true、-Pverbose=true、--no-daemon 等
    ......
    try {
      exitCode = await _processUtils.stream(
        command,
        workingDirectory: project.android.hostAppGradleRoot.path,
        allowReentrantFlutter: true,
        environment: <String, String>{if (javaPath != null)
            'JAVA_HOME': javaPath,
        },
        mapFunction: consumeLog,
      );
    } on ProcessException catch (exception) {......} finally {status.stop();
    }
    ......
  }
  ......
}

哈哈，假相了，这下配合《Flutter Android 工程构造及应用层编译源码深入分析》一文首尾呼应后你应该彻底明确 Flutter android apk 是怎么编译的流程！

总结

当初咱们联合《Flutter Android 工程构造及应用层编译源码深入分析》和这篇进行关联总结，能够总结出执行 flutter build apk 命令背地的大抵主流程如下：

既然执行 flutter build apk 命令你都搞明确了，那么其余 flutter 相干的任何命令你是否也能够本人触类旁通进行剖析学习，实质都一样哈。因为我这里工夫无限，所以对于 flutter pub get、flutter doctor 等其余命令不再做详细分析。

正文完
flutter
发表至： flutter
2021-08-22
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