背景
上一篇《Flutter Android 工程結構及應用層編譯原始碼深入分析》我們分析了 Flutter Android 相關的應用層主要編譯流程，其中分析到底層本質命令工具【Flutter SDK 下bin/flutter編譯命令分析】小節時只提到，我們執行任何 flutter 命令的本質都是把引數傳遞到了FLUTTER_SDK_DIR/packages/flutter_tools/bin/flutter_tools.dart原始碼的 main 方法中，沒有對這里面進行深入分析，本文要做的事就是層層遞進揭開這里的本質，并與上篇呼應解釋編譯產物的由來，
flutter_tools 介紹
通過flutter -h命令我們可以直觀全域感受都支持哪些引數，有些引數還有子引數，我們所執行的所有引數本質都走進了下面模塊的原始碼入口中，
因此我們如果直接想從原始碼方式使用 flutter tools，則可以直接當前目錄中如下命令：
# ARGS 就是一堆引數，譬如我們上篇的 build apk
dart bin/flutter_tools.dart ARGS
如果想重新生成 Flutter Tools snapshot，可以直接當前目錄中執行如下命令：
rm ../../bin/cache/flutter_tools.stamp ../../bin/cache/flutter_tools.snapshot
這樣就成功洗掉了上篇中 shell 腳本呼叫的 Flutter Tools snapshot，然后在執行時會自動重新生成一個，
原始碼分析
上面既然交代了整個背景，那么我們接下來就基于 Flutter SDK 入口packages/flutter_tools/bin/flutter_tools.dart開始分析，整個分析繼續承接上篇flutter build apk命令，如下：
//1、匯入packages/flutter_tools/lib/executable.dart檔案
import 'package:flutter_tools/executable.dart' as executable;
//2、入口重點，執行executable.main方法，并將我們`build apk`引數傳入
void main(List<String> args) {
executable.main(args);
}
接下來我們去packages/flutter_tools/lib/executable.dart看看他的 main 方法，如下：
Future<void> main(List<String> args) async {
//一堆引數決議判斷啥的，譬如決議flutter doctor的doctor引數啥的
......
//1、重點！runner的本質是import 'runner.dart' as runner;
// 本質就是呼叫run方法的各種引數傳遞，重點關注第一個和第二個引數即可
await runner.run(
args,
() => generateCommands(
verboseHelp: verboseHelp,
verbose: verbose,
),
......,
);
}
//2、步驟1中runner.run的第二個核心引數方法定義
//FlutterCommand為packages/flutter_tools/lib/src/runner/flutter_command.dart中定義的抽象類
//這個方法本質就是把flutter執行的命令引數串列全部加入串列，類似命令模式
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(),
];
......
讓我們把目光先移動到runner.dart檔案的 run 方法，然后回過頭來看上面代碼中的步驟1如何呼叫步驟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、創建runner物件實體，并把上一片段代碼中步驟2方法回傳的FlutterCommand串列追加進runner中
final FlutterCommandRunner runner = FlutterCommandRunner(verboseHelp: verboseHelp);
commands().forEach(runner.addCommand);
......
return runZoned<Future<int>>(() async {
try {
//3、依據args引數執行runner實體的run方法
await runner.run(args);
......
} catch (error, stackTrace) { // ignore: avoid_catches_without_on_clauses
......
}
}, one rror: (Object error, StackTrace stackTrace) async { // ignore: deprecated_member_use
......
});
}, overrides: overrides);
}
可以看到，首先實體化了一個 FlutterCommandRunner 物件，接著把所有支持的 FlutterCommand 串列加入 runner 物件中，然后呼叫了 runner 的 run 方法，所以我們現在查看packages/flutter_tools/lib/src/runner/flutter_command_runner.dart檔案的 run 方法，如下：
......
@override
Future<void> run(Iterable<String> args) {
......
//本質呼叫了父類CommandRunner的run方法，run方法呼叫了子類FlutterCommandRunner的runCommand方法
//子類FlutterCommandRunner的runCommand最終又呼叫了父類CommandRunner的runCommand方法
return super.run(args);
}
......
所以我們接下來看父類 CommandRunner 的 runCommand 方法，如下：
Future<T?> runCommand(ArgResults topLevelResults) async {
//1、flutter命令后面傳遞進來引數，譬如build apk
var argResults = topLevelResults;
//2、前面分析過的，runner中添加的支持命令串列
var commands = _commands;
//3、定義一個Command變數，用來最終依據引數賦值為對應的Command物件實體
Command? command;
var commandString = executableName;
//4、while條件為真，因為commands為支持的引數串列
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、執行對應命令的run方法
return (await command.run()) as T?;
}
......
}
可以看到，這就是一個標準的命令模式設計，先把支持的命令添加到串列，然后依據引數遍歷匹配對應命令進行執行，下面我們以flutter build apk命令為例來看其對應的 BuildCommand 命令（packages/flutter_tools/lib/src/commands/build.dart）實作，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));
}
//上一小段代碼中command = commands[argResults.name]就是這么得到的
//name=build就是執行flutter build apk中的build字串
@override
final String name = 'build';
@override
final String description = 'Build an executable app or install bundle.';
@override
Future<FlutterCommandResult> runCommand() async => null;
}
可以看到，任意一個命令基本都繼承自 FlutterCommand 實作，命令的執行都是呼叫了 FlutterCommand 的 run 方法，如下：
abstract class FlutterCommand extends Command<void> {
......
//runner物件中最終執行呼叫的方法是這個
@override
Future<void> run() {
......
return context.run<void>(
name: 'command',
overrides: <Type, Generator>{FlutterCommand: () => this},
body: () async {
......
try {
//見名知意，先校驗再運行命令
commandResult = await verifyThenRunCommand(commandPath);
} finally {
......
}
},
);
}
......
@mustCallSuper
Future<FlutterCommandResult> verifyThenRunCommand(String commandPath) async {
//1、如果需要更新快取就先更新快取
if (shouldUpdateCache) {
await globals.cache.updateAll(<DevelopmentArtifact>{DevelopmentArtifact.universal});
await globals.cache.updateAll(await requiredArtifacts);
}
globals.cache.releaseLock();
//2、校驗命令
await validateCommand();
//3、如果需要先執行pub就先執行，譬如pub get下載依賴
if (shouldRunPub) {
......
//4、執行pub get下載依賴，即下載pubspec.yaml里配置的依賴
await pub.get(
context: PubContext.getVerifyContext(name),
generateSyntheticPackage: project.manifest.generateSyntheticPackage,
checkUpToDate: cachePubGet,
);
await project.regeneratePlatformSpecificTooling();
if (reportNullSafety) {
await _sendNullSafetyAnalyticsEvents(project);
}
}
setupApplicationPackages();
......
//5、真正開始執行命令
return runCommand();
}
}
繞一圈最終我們又回到 BuildCommand 類，可以發現其 runCommand 方法重寫為空實作，而其構造時通過 addSubcommand 方法追加了很多子命令，譬如執行flutter build aar編譯 aar 的 BuildAarCommand 命令、執行flutter build apk編譯 apk 的 BuildApkCommand 命令，整個 sub command 與其宿主又算是一個責任鏈，所以上面同樣的套路順序對于 sub command 同樣適用，因此我們去看下編譯 apk 產物的 BuildApkCommand 原始碼（packages/flutter_tools/lib/src/commands/build_apk.dart），如下：
class BuildApkCommand extends BuildSubCommand {
BuildApkCommand({bool verboseHelp = false}) {
......
//一堆引數的確認
}
//對應flutter build apk里面子命令字串apk
@override
final String name = 'apk';
......
//本質命令執行方法
@override
Future<FlutterCommandResult> runCommand() async {
......
//呼叫androidBuilder的buildApk方法進行真正的編譯，目測里面的產物也就是上一篇文章分析的那些
//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();
}
}
順著這條路我們繼續跟進位于packages/flutter_tools/lib/src/android/android_builder.dart的 androidBuilder 屬性的 buildApk 方法，如下：
//本質是packages/flutter_tools/lib/src/context_runner.dart中context.run方法中的AndroidGradleBuilder實體
AndroidBuilder get androidBuilder {
return context.get<AndroidBuilder>();
}
//抽象類定義，AndroidBuilder
abstract class AndroidBuilder {
const AndroidBuilder();
// 定義編譯aar的方法
Future<void> buildAar({
@required FlutterProject project,
@required Set<AndroidBuildInfo> androidBuildInfo,
@required String target,
@required String outputDirectoryPath,
@required String buildNumber,
});
// 定義編譯apk的方法
Future<void> buildApk({
@required FlutterProject project,
@required AndroidBuildInfo androidBuildInfo,
@required String target,
});
// 定義編譯aab的方法
Future<void> buildAab({
@required FlutterProject project,
@required AndroidBuildInfo androidBuildInfo,
@required String target,
bool validateDeferredComponents = true,
bool deferredComponentsEnabled = false,
});
}
所以我們繼續去看 AndroidGradleBuilder 實作類（packages/flutter_tools/lib/src/android/gradle.dart）的 buildApk 方法，如下：
class AndroidGradleBuilder implements AndroidBuilder {
AndroidGradleBuilder({
......
}) : ......;
......
//1、編譯 apk 的方法
@override
Future<void> buildApk({
@required FlutterProject project,
@required AndroidBuildInfo androidBuildInfo,
@required String target,
}) async {
//2、呼叫
await buildGradleApp(
project: project,
androidBuildInfo: androidBuildInfo,
target: target,
isBuildingBundle: false,
localGradleErrors: gradleErrors,
);
}
......
//3、真的編譯
Future<void> buildGradleApp({
@required FlutterProject project, //FlutterProject.current()
@required AndroidBuildInfo androidBuildInfo, //build configuration
@required String target, //dart代碼入口，預設lib/main.dart
@required bool isBuildingBundle, //是aab還是apk，默認false則apk
@required List<GradleHandledError> localGradleErrors,
bool shouldBuildPluginAsAar = false, //是不是將插件編譯為aar
bool validateDeferredComponents = true,
bool deferredComponentsEnabled = false,
int retries = 1,
}) async {
//4、檢查支持的android版本，獲取android編譯產物目錄，即gradle中配置的build產物目錄，默認為專案根目錄下的build目錄
if (!project.android.isSupportedVersion) {
_exitWithUnsupportedProjectMessage(_usage, _logger.terminal);
}
final Directory buildDirectory = project.android.buildDirectory;
//5、讀取安卓相關屬性檔案判斷是否使用androidx，然后發送編譯事件引數
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、更新安卓專案中local.properties中的versionName和versionCode值，值來自于public.yaml檔案配置
updateLocalProperties(project: project, buildInfo: androidBuildInfo.buildInfo);
//7、編譯aar的話就走buildPluginsAsAar方法進行
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、獲取編譯apk或者aab對應的標準安卓task name，構建引數等資訊，也就是gradle命令后面一堆的引數構造
final BuildInfo buildInfo = androidBuildInfo.buildInfo;
final String assembleTask = isBuildingBundle
? getBundleTaskFor(buildInfo)
: getAssembleTaskFor(buildInfo);
......
final List<String> command = <String>[
_gradleUtils.getExecutable(project),
];
......
//9、依據條件追加command的一堆引數，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，真相了，這下配合《Flutter Android 工程結構及應用層編譯原始碼深入分析》一文首尾呼應后你應該徹底明白 Flutter android apk 是怎么編譯的流程！
總結
現在我們結合《Flutter Android 工程結構及應用層編譯原始碼深入分析》和這篇進行關聯總結，可以總結出執行flutter build apk命令背后的大致主流程如下：
既然執行flutter build apk命令你都搞明白了，那么其他 flutter 相關的任何命令你是否也可以自己舉一反三進行分析學習，本質都一樣哈，由于我這里時間有限，所以對于flutter pub get、flutter doctor等其他命令不再做詳細分析，
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標籤：其他