源碼解讀Flutter tools機制

一倒堕、Flutter tools命令

1.1 概述

開發(fā)Flutter應用過程专控，經常會用過Flutter命令，比如flutter run可用于安裝并運行Flutter應用，flutter build可用于構建產物驯杜，相信有不少人會好奇flutter命令背后的原理。對于flutter命令的起點位于flutter sdk中路徑/flutter/bin/目錄中的flutter命令，該命令最終會調用到flutter/packages/flutter_tools工程袖迎。

1.2 flutter命令參數表

列舉Flutter命令、對應類以及說明腺晾，實現見下文[小節(jié)2.3]燕锥。

名稱	對應類	說明
create	CreateCommand	創(chuàng)建新的Flutter項目
build	BuildCommand	Flutter構建命令
install	InstallCommand	安裝Flutter應用到已連接設備
run	RunCommand	運行Flutter應用于已連接設備
packages	PackagesCommand	管理Flutter包的命令
devices	DevicesCommand	列出所有已連接的設備
emulators	EmulatorsCommand	列出，啟動悯蝉，創(chuàng)建模擬器
attach	AttachCommand	附加到正在運行的應用程序
trace	TraceCommand	開始和停止跟蹤正在運行的Flutter應用程序
logs	LogsCommand	顯示Flutter應用運行中的log
doctor	DoctorCommand	顯示關于已安裝工具的信息
upgrade	UpgradeCommand	升級Flutter
clean	CleanCommand	刪除build/和.dart_tool/ 目錄
analyze	AnalyzeCommand	分析項目Dart代碼
format	FormatCommand	格式化一個或多個dart文件
config	ConfigCommand	配置Flutter settings
drive	DriveCommand	為當前項目運行Flutter Driver測試
test	TestCommand	為當前項目運行Flutter 單元測試

另外归形，對于flutter build有子命令，其子命令的對應類及說明如下：

命令	對應類	說明
build aot	BuildAotCommand	構建AOT編譯產物
build apk	BuildApkCommand	構建Android APK
build ios	BuildIOSCommand	構建iOS應用bundle
build appbundle	BuildAppBundleCommand	構建Android應用bundle
build bundle	BuildBundleCommand	構建Flutter assets

比如flutter run則執(zhí)行RunCommand.runCommand()鼻由，flutter install則執(zhí)行InstallCommand.runCommand()暇榴。

二、深入源碼flutter命令

2.1 flutter命令起點

[-> /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"

//真正的執(zhí)行邏輯
"$DART" $FLUTTER_TOOL_ARGS "$SNAPSHOT_PATH" "$@"

該方法功能：

$DART：是指$ FLUTTER_ROOT/bin/cache/dart-sdk/bin/dart蕉世；
$SNAPSHOT\_PATH：是指$ FLUTTER_ROOT/bin/cache/flutter_tools.snapshot蔼紧，這是由packages/flutter_tools項目編譯所生成的產物文件。

那么flutter命令等價于如下：

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

dart執(zhí)行flutter_tools.snapshot狠轻，其實也就是執(zhí)行flutter_tools.dart的main()方法奸例，也就是說將上述命令改為如下語句，則運行flutter命令可以執(zhí)行本地flutter_tools的項目代碼向楼，可用于本地調試分析查吊。

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

接下來，執(zhí)行流程進入flutter/packages/flutter_tools/目錄湖蜕。

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);  //[見小節(jié)2.3]
}

2.3 executable.main

[-> lib/executable.dart]

import 'runner.dart' as runner;

Future<void> main(List<String> args) async {
  ...
  //[見小節(jié)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,
}) {
  ...
  //創(chuàng)建FlutterCommandRunner對象
  final FlutterCommandRunner runner = FlutterCommandRunner(verboseHelp: verboseHelp);
  //[見小節(jié)2.4.1] 將創(chuàng)建的命令對象都加入到_commands
  commands.forEach(runner.addCommand);

  return runInContext<int>(() async {
    ...
    // [見小節(jié)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逻卖。比如flutter run對應的命令對象為RunCommand，flutter build對應的命令對象為buildCommand重荠。

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); // [見小節(jié)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))); //見下文

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

    while (commands.isNotEmpty) {
      ...
      argResults = argResults.command;
      //根據命令名從命令列表中找到相應的命令
      command = commands[argResults.name];
      command._globalResults = topLevelResults;
      command._argResults = argResults;
      commands = command._subcommands;  //查找到子命令
      commandString += " ${argResults.name}";
    }
    // 執(zhí)行真正對應命令的run()方法 [見小節(jié)2.7]
    return (await command.run()) as T;
  }
}

該方法會根據命令后通過循環(huán)遍歷查找子命令箭阶，直到找到最后的命令為止。但這些命令都直接或者間接繼承于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 {
          // [見小節(jié)2.8]
          commandResult = await verifyThenRunCommand(commandPath);
        } on ToolExit {
          commandResult = const FlutterCommandResult(ExitStatus.fail);
          rethrow;
        } finally {
          ...
        }
      },
    );
  }
}

2.8 FlutterCommand.verifyThenRunCommand