源码解读Flutter tools机制

2022-11-23 本文已影响0人蜗牛是不是牛

一、Flutter tools命令

开发Flutter应用过程，经常会用过Flutter命令，比如flutter run可用于安装并运行Flutter应用，flutter build可用于构建产物，相信有不少人会好奇flutter命令背后的原理。对于flutter命令的起点位于flutter sdk中路径/flutter/bin/目录中的flutter命令，该命令最终会调用到flutter/packages/flutter_tools工程。

二、深入源码flutter命令

2.1 flutter命令起点

[-> /flutter/bin/flutter]

...
FLUTTER_TOOLS_DIR="$FLUTTER_ROOT/packages/flutter_tools"
SNAPSHOT_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.snapshot"
STAMP_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.stamp"
SCRIPT_PATH="$FLUTTER_TOOLS_DIR/bin/flutter_tools.dart"
DART_SDK_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk"

DART="$DART_SDK_PATH/bin/dart"
PUB="$DART_SDK_PATH/bin/pub"

//真正的执行逻辑
"$DART" $FLUTTER_TOOL_ARGS "$SNAPSHOT_PATH" "$@"

该方法功能：

$DART：是指$ FLUTTER_ROOT/bin/cache/dart-sdk/bin/dart；
$SNAPSHOT_PATH：是指$ FLUTTER_ROOT/bin/cache/flutter_tools.snapshot，这是由packages/flutter_tools项目编译所生成的产物文件。

那么flutter命令等价于如下：

/bin/cache/dart-sdk/bin/dart $FLUTTER_TOOL_ARGS "bin/cache/flutter_tools.snapshot" "$@"

dart执行flutter_tools.snapshot，其实也就是执行flutter_tools.dart的main()方法，也就是说将上述命令改为如下语句，则运行flutter命令可以执行本地flutter_tools的项目代码，可用于本地调试分析。

/bin/cache/dart-sdk/bin/dart $FLUTTER_TOOL_ARGS "$FLUTTER_ROOT/packages/flutter_tools/bin/flutter_tools.dart" "$@"

接下来，执行流程进入flutter/packages/flutter_tools/目录。

2.2 flutter_tools.main

[-> flutter/packages/flutter_tools/bin/flutter_tools.dart]

import 'package:flutter_tools/executable.dart' as executable;

void main(List<String> args) {
  executable.main(args);  //[见小节2.3]
}

2.3 executable.main

[-> lib/executable.dart]

import 'runner.dart' as runner;

Future<void> main(List<String> args) async {
  ...
  //[见小节2.4]
  await runner.run(args, <FlutterCommand>[
    AnalyzeCommand(verboseHelp: verboseHelp),
    AttachCommand(verboseHelp: verboseHelp),
    BuildCommand(verboseHelp: verboseHelp),
    ChannelCommand(verboseHelp: verboseHelp),
    CleanCommand(),
    ConfigCommand(verboseHelp: verboseHelp),
    CreateCommand(),
    DaemonCommand(hidden: !verboseHelp),
    DevicesCommand(),
    DoctorCommand(verbose: verbose),
    DriveCommand(),
    EmulatorsCommand(),
    FormatCommand(),
    GenerateCommand(),
    IdeConfigCommand(hidden: !verboseHelp),
    InjectPluginsCommand(hidden: !verboseHelp),
    InstallCommand(),
    LogsCommand(),
    MakeHostAppEditableCommand(),
    PackagesCommand(),
    PrecacheCommand(),
    RunCommand(verboseHelp: verboseHelp),
    ScreenshotCommand(),
    ShellCompletionCommand(),
    StopCommand(),
    TestCommand(verboseHelp: verboseHelp),
    TraceCommand(),
    TrainingCommand(),
    UpdatePackagesCommand(hidden: !verboseHelp),
    UpgradeCommand(),
    VersionCommand(),
  ], verbose: verbose,
     muteCommandLogging: muteCommandLogging,
     verboseHelp: verboseHelp,
     overrides: <Type, Generator>{
       CodeGenerator: () => const BuildRunner(),
     });
}

2.4 runner.run

[-> lib/runner.dart]

Future<int> run(
  List<String> args,
  List<FlutterCommand> commands, {
  bool muteCommandLogging = false,
  bool verbose = false,
  bool verboseHelp = false,
  bool reportCrashes,
  String flutterVersion,
  Map<Type, Generator> overrides,
}) {
  ...
  //创建FlutterCommandRunner对象
  final FlutterCommandRunner runner = FlutterCommandRunner(verboseHelp: verboseHelp);
  //[见小节2.4.1] 将创建的命令对象都加入到_commands
  commands.forEach(runner.addCommand);

  return runInContext<int>(() async {
    ...
    // [见小节2.5]
    await runner.run(args);
    ...
  }, overrides: overrides);
}

2.4.1 addCommand

[-> package:args/command_runner.dart]

void addCommand(Command<T> command) {
  var names = [command.name]..addAll(command.aliases);
  for (var name in names) {
    _commands[name] = command;
    argParser.addCommand(name, command.argParser);
  }
  command._runner = this;
}

所有命令都加入到_commands。比如flutter run对应的命令对象为RunCommand，flutter build对应的命令对象为buildCommand。

2.5 FlutterCommandRunner.run

[-> lib/src/runner/flutter_command_runner.dart]

class FlutterCommandRunner extends CommandRunner<void> {

  Future<void> run(Iterable<String> args) {
    return super.run(args); // [见小节2.6]
  }
}

2.6 CommandRunner.run

[-> package:args/command_runner.dart]

class CommandRunner<T> {

  Future<T> run(Iterable<String> args) =>
      new Future.sync(() => runCommand(parse(args))); //见下文

  Future<T> runCommand(ArgResults topLevelResults) async {
    var argResults = topLevelResults;
    var commands = _commands;
    Command command;
    var commandString = executableName;

    while (commands.isNotEmpty) {
      ...
      argResults = argResults.command;
      //根据命令名从命令列表中找到相应的命令
      command = commands[argResults.name];
      command._globalResults = topLevelResults;
      command._argResults = argResults;
      commands = command._subcommands;  //查找到子命令
      commandString += " ${argResults.name}";
    }
    // 执行真正对应命令的run()方法 [见小节2.7]
    return (await command.run()) as T;
  }
}

该方法会根据命令后通过循环遍历查找子命令，直到找到最后的命令为止。但这些命令都直接或者间接继承于FlutterCommand命令

2.7 FlutterCommand.run

[-> lib/src/runner/flutter_command.dart]

abstract class FlutterCommand extends Command<void> {

  Future<void> run() {
    final DateTime startTime = systemClock.now();

    return context.run<void>(
      name: 'command',
      overrides: <Type, Generator>{FlutterCommand: () => this},
      body: () async {
        ...
        try {
          // [见小节2.8]
          commandResult = await verifyThenRunCommand(commandPath);
        } on ToolExit {
          commandResult = const FlutterCommandResult(ExitStatus.fail);
          rethrow;
        } finally {
          ...
        }
      },
    );
  }
}

2.8 FlutterCommand.verifyThenRunCommand