AGP资源链接之LinkApplicationAndroidResourcesTask流程分析

AGP / Gradle

查找实现类

AGP link资源的过程所执行task的名称叫processDebugResource，我们需要根据task名称找到具体的实现类，Gradle提供了一个很实用的命令，可根据任务名查询实现类。

./gradlew help –task

查找processDebugResources:

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$ ./gradlew help --task processDebugResources
> Task :help
Detailed task information for processDebugResources
Path
     :app:processDebugResources
Type
     LinkApplicationAndroidResourcesTask (com.android.build.gradle.internal.res.LinkApplicationAndroidResourcesTask)
Description
     -
Group
     -

从终端的输出信息我们可以发现具体的实现类为com.android.build.gradle.internal.res.LinkApplicationAndroidResourcesTask。

流程分析

本次分析的AGP源码版本7.2.2

LinkApplicationAndroidResourcesTask虽然也继承至IncrementalTask，但实际上该任务每次都会处理合并任务的全量结果集。虽然说LinkApplicationAndroidResourcesTask可以解析合并后资源的变化，但是因为link流程限制的原因：没有中间状态或缓存则无从处理变化的资源文件。
因为LinkApplicationAndroidResourcesTask每次都是全量编译，我们直接看doFullTaskAction方法：

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fun doFullTaskAction(inputStableIdsFile: File?) {
        workerExecutor.noIsolation().submit(TaskAction::class.java) { parameters ->
            //配置了很多参数
            parameters.initializeFromAndroidVariantTask(this)

            parameters.mainDexListProguardOutputFile.set(mainDexListProguardOutputFile)
            parameters.outputStableIdsFile.set(stableIdsOutputFileProperty)
            parameters.proguardOutputFile.set(proguardOutputFile)
            parameters.rClassOutputJar.set(rClassOutputJar)
            parameters.resPackageOutputDirectory.set(resPackageOutputFolder)
            parameters.sourceOutputDirectory.set(sourceOutputDirProperty)
            parameters.symbolsWithPackageNameOutputFile.set(symbolsWithPackageNameOutputFile)
            parameters.textSymbolOutputFile.set(textSymbolOutputFileProperty)

            parameters.androidJarInput.set(androidJarInput)
            parameters.aapt2.set(aapt2)
            parameters.symbolTableBuildService.set(symbolTableBuildService)

            parameters.aaptOptions.set(AaptOptions(noCompress.orNull, aaptAdditionalParameters.orNull))
            parameters.applicationId.set(applicationId)
            parameters.buildTargetDensity.set(buildTargetDensity)
            parameters.canHaveSplits.set(canHaveSplits)
            parameters.compiledDependenciesResources.from(compiledDependenciesResources)
            parameters.dependencies.from(dependenciesFileCollection)
            parameters.featureResourcePackages.from(featureResourcePackages)
            parameters.imports.from(sharedLibraryDependencies)
            parameters.incrementalDirectory.set(incrementalFolder)
            parameters.inputResourcesDirectory.set(inputResourcesDir)
            parameters.inputStableIdsFile.set(inputStableIdsFile)
            parameters.library.set(isLibrary)
            parameters.localResourcesFile.set(localResourcesFile)
            parameters.manifestFiles.set(if (aaptFriendlyManifestFiles.isPresent) aaptFriendlyManifestFiles else manifestFiles)
            parameters.manifestMergeBlameFile.set(manifestMergeBlameFile)
            parameters.mergeBlameDirectory.set(mergeBlameLogFolder)
            parameters.namespace.set(namespace)
            parameters.namespaced.set(isNamespaced)
            parameters.packageId.set(resOffset)
            parameters.resourceConfigs.set(resourceConfigs)
            parameters.sharedLibraryDependencies.from(sharedLibraryDependencies)
            parameters.sourceSetMaps.from(sourceSetMaps)
            parameters.useConditionalKeepRules.set(useConditionalKeepRules)
            parameters.useFinalIds.set(useFinalIds)
            parameters.useMinimalKeepRules.set(useMinimalKeepRules)
            parameters.useStableIds.set(useStableIds)
            parameters.variantName.set(variantName)
            parameters.variantOutputs.set(variantOutputs.get().map { it.toSerializedForm() })
            parameters.variantType.set(type)
        }
    }

这里使用到AGP自己内部的workerExecutor并行执行，触发TaskAction到run方法：

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abstract class TaskAction : ProfileAwareWorkAction<TaskWorkActionParameters>() {

       @get:Inject
       abstract val workerExecutor: WorkerExecutor

       override fun run() {
           //合并后的Manifest工件
           val manifestBuiltArtifacts = BuiltArtifactsLoaderImpl().load(parameters.manifestFiles)
               ?: throw RuntimeException("Cannot load processed manifest files, please file a bug.")
           // 'Incremental' runs should only preserve the stable IDs file.
           FileUtils.deleteDirectoryContents(parameters.resPackageOutputDirectory.get().asFile)

           val variantOutputsList: List<VariantOutputImpl.SerializedForm> = parameters.variantOutputs.get()
           val mainOutput = chooseOutput(variantOutputsList)

           invokeAaptForSplit(
                   mainOutput,
                   manifestBuiltArtifacts.getBuiltArtifact(mainOutput.variantOutputConfiguration)
                       ?: throw RuntimeException("Cannot find built manifest for $mainOutput"),
                   true,
                   parameters.aapt2.get().getLeasingAapt2(),
                   parameters.inputStableIdsFile.orNull?.asFile, parameters
           )
       	//...
       }
       //...
}

aapt2 link的过程，指定构建的Android清单文件的路径是一个必须的配置，因为清单文件中包含应用的基本信息（如软件包名称和应用ID)。
内部调用invokeAaptForSplit方法：

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private fun invokeAaptForSplit(
        variantOutput: VariantOutputImpl.SerializedForm,
        manifestOutput: BuiltArtifactImpl,
        generateRClass: Boolean,
        aapt2: Aapt2,
        stableIdsInputFile: File?,
        parameters: TaskWorkActionParameters) {

        //...
        val resOutBaseNameFile =
            getOutputBaseNameFile(variantOutput,
                parameters.resPackageOutputDirectory.get().asFile
        )//link过程中的输出文件路径build/intermediates/processed_res/debug/out/resources-debug.ap_
        val manifestFile = manifestOutput.outputFile
        //...
        try {

            // If the new resources flag is enabled and if we are dealing with a library process
            // resources through the new parsers
            run {
                //构建configBuilder
                val configBuilder = AaptPackageConfig.Builder()
                    .setManifestFile(File(manifestFile))//合并后的AndroidManifest的文件路径
                    .setOptions(parameters.aaptOptions.get())
                    .setCustomPackageForR(packageForR)
                    .setSymbolOutputDir(symbolOutputDir)
                    .setSourceOutputDir(srcOut)
                    .setResourceOutputApk(resOutBaseNameFile)//设置link过程的输出文件路径
                    .setProguardOutputFile(proguardOutputFile)
                    .setMainDexListProguardOutputFile(mainDexListProguardOutputFile)
                    .setVariantType(parameters.variantType.get())
                    .setResourceConfigs(parameters.resourceConfigs.get())
                    .setPreferredDensity(preferredDensity)
                    .setPackageId(parameters.packageId.orNull)
                    .setAllowReservedPackageId(
                        parameters.packageId.isPresent && parameters.packageId.get() < FeatureSetMetadata.BASE_ID
                    )
                    .setDependentFeatures(featurePackagesBuilder.build())
                    .setImports(parameters.imports.files)
                    .setIntermediateDir(parameters.incrementalDirectory.get().asFile)
                    .setAndroidJarPath(parameters.androidJarInput.get()
                        .getAndroidJar()
                        .get().absolutePath)//平台的android.jar的路径
                    .setUseConditionalKeepRules(parameters.useConditionalKeepRules.get())
                    .setUseMinimalKeepRules(parameters.useMinimalKeepRules.get())
                    .setUseFinalIds(parameters.useFinalIds.get())
                    .setEmitStableIdsFile(parameters.outputStableIdsFile.orNull?.asFile)
                    .setConsumeStableIdsFile(stableIdsInputFile)
                    .setLocalSymbolTableFile(parameters.localResourcesFile.orNull?.asFile)
                    .setMergeBlameDirectory(parameters.mergeBlameDirectory.get().asFile)
                    .setManifestMergeBlameFile(parameters.manifestMergeBlameFile.orNull?.asFile)
                    .apply {
                        val compiledDependencyResourceFiles =
                            parameters.compiledDependenciesResources.files
                        // In the event of running process[variant]AndroidTestResources
                        // on a module that depends on a module with no precompiled resources,
                        // we must avoid passing the compiled resource directory to AAPT link.
                        if (compiledDependencyResourceFiles.all(File::exists)) {
                            //添加依赖库中的编译文件
                            addResourceDirectories(
                                compiledDependencyResourceFiles.reversed().toImmutableList())
                        }
                    }

                if (parameters.namespaced.get()) {
                    configBuilder.setStaticLibraryDependencies(ImmutableList.copyOf(parameters.dependencies.files))
                } else {
                    if (generateRClass) {
                        //生生成R.txt文件
                        configBuilder.setLibrarySymbolTableFiles(parameters.dependencies.files)
                    }
                    //添加资源编译任务的产物,build/intermediates/merged_res/debug/目录的文件
                    configBuilder.addResourceDir(checkNotNull(parameters.inputResourcesDirectory.orNull?.asFile))
                }

                val logger = Logging.getLogger(LinkApplicationAndroidResourcesTask::class.java)

                configBuilder.setIdentifiedSourceSetMap(
                        mergeIdentifiedSourceSetFiles(
                                parameters.sourceSetMaps.files.filterNotNull())
                )
                //触发link动作
                processResources(
                    aapt = aapt2,
                    aaptConfig = configBuilder.build(),
                    rJar = if (generateRClass) parameters.rClassOutputJar.orNull?.asFile else null,
                    logger = logger,
                    errorFormatMode = parameters.aapt2.get().getErrorFormatMode(),
                    symbolTableLoader = parameters.symbolTableBuildService.get()::loadClasspath,
                )

                if (LOG.isInfoEnabled) {
                    LOG.info("Aapt output file {}", resOutBaseNameFile.absolutePath)
                }
            }

            if (generateRClass
                && (parameters.library.get() || !parameters.dependencies.files.isEmpty())
                && parameters.symbolsWithPackageNameOutputFile.isPresent
            ) {
                SymbolIo.writeSymbolListWithPackageName(
                    parameters.textSymbolOutputFile.orNull?.asFile!!.toPath(),
                    packageForR,
                    parameters.symbolsWithPackageNameOutputFile.get().asFile.toPath()
                )
            }
            appendOutput(
                parameters.applicationId.get().orEmpty(),
                parameters.variantName.get(),
                manifestOutput.newOutput(
                    resOutBaseNameFile.toPath()
                ),
                parameters.resPackageOutputDirectory.get().asFile
            )
        } catch (e: ProcessException) {
            throw BuildException(
                "Failed to process resources, see aapt output above for details.", e
            )
        }
    }

invokeAaptForSplit这个方法很长，省去很多其它不那么重要的代码方便阅读。通过建造者构建一个configBuilder对象，可以看到有很多配置。其中有一些关键的配置需要说明一下：
processDebugResource任务会输出一个resources-debug.ap_压缩文件，setResourceOutputApk就是在配置压缩文件的路径——build/intermediates/processed_res/debug/out/resources-debug.ap_
setAndroidJarPath是在设置平台的android.jar路径，link的过程会使用android.jar 中包含的API信息来验证你的代码。
addResourceDirectories使用设置远程依赖库中的*.flat文件，configBuilder.addResourceDir设置项目build/intermediates/merged_res/debug/目录下的*.flat文件。
配置这些数据都是为后面的link作准备，直接进入processResources方法：

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fun processResources(
    aapt: Aapt2,
    aaptConfig: AaptPackageConfig,
    rJar: File?,
    logger: Logger,
    errorFormatMode: SyncOptions.ErrorFormatMode,
    symbolTableLoader: (Iterable<File>) -> List<SymbolTable> = { SymbolIo().loadDependenciesSymbolTables(it) }
) {

    try {
        aapt.link(aaptConfig, LoggerWrapper(logger))
    } catch (e: Aapt2Exception) {
        throw rewriteLinkException(
            e,
            errorFormatMode,
            aaptConfig.mergeBlameDirectory,
            aaptConfig.manifestMergeBlameFile,
            aaptConfig.identifiedSourceSetMap,
            logger
        )
    } catch (e: Aapt2InternalException) {
        throw e
    } catch (e: Exception) {
        throw ProcessException("Failed to execute aapt", e)
    }
    //...
}

在上篇分析MergeResources流程分析的文章中知道aapt的实例对象是PartialInProcessResourceProcessor，内部调用delegate的link方法，最终调用的是Aapt2DaemonImpl的link方法：

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abstract class Aapt2Daemon(
        protected val displayName: String,
        protected val logger: ILogger) : Aapt2 {
	override fun link(request: AaptPackageConfig, logger: ILogger) {
        checkStarted()//检查aapt进程是开启
        try {
            doLink(request, logger)//调用
        } catch (e: Aapt2Exception) {
            // Propagate errors in the users sources directly.
            throw e
        } catch (e: TimeoutException) {
            handleError("Link timed out", e)
        } catch (e: Exception) {
            handleError("Unexpected error during link", e)
        }
    }
    //...
}

checkStarted流程在MergeResources流程分析已经看过，Aapt2DaemonImpl的doLink：

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class Aapt2DaemonImpl(
    displayId: String,
    private val aaptPath: String,
    private val aaptCommand: List<String>,
    versionString: String,
    private val daemonTimeouts: Aapt2DaemonTimeouts,
    logger: ILogger) :
Aapt2Daemon(
    displayName = "AAPT2 $versionString Daemon $displayId",
    logger = logger){
     override fun doLink(request: AaptPackageConfig, logger: ILogger) {
        val waitForTask = WaitForTaskCompletion(displayName, logger)
        try {
            processOutput.delegate = waitForTask
            Aapt2DaemonUtil.requestLink(writer, request)
            val result = waitForTask.future.get(daemonTimeouts.link, daemonTimeouts.linkUnit)
           //...
        } finally {
            processOutput.delegate = noOutputExpected
        }
    }
}

Aapt2DaemonUtil.requestLink方法是往aapt进程的写入句柄输入参数并flush，然后读取link命令的执行结果。具体各个参数的说明大家可以参考link_options官方文档。

结语

LinkApplicationAndroidResourcesTask相比MergeResouces的过程要简单很多，只是启动了一个appt进程，把编译后的*.flat产物给aapt进程处理生产产物。
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