前言

现在大部分混合应用使用了React Naitve,在Debug模式下随着工程不断的叠加庞大，加上本身工程没有做组件化，使得每次工程编译时间大大增加。

一、Android React Native混合工程编译分析

首先我们切到工程的主Gradle文件，可以发现主Gradle引入了React的编译脚本如下所示

project.ext.react = [
        root         : "../..",
        bundleInDebug: true,
]
apply from: "../../node_modules/react-native/react.gradle"

bundleInDebug默认为false,但是大部分工程首页一般都会有引用RN的部分页面，如果这里不设置为true的话，进入首页会引起首页黑屏。所以一般这边的值都会设置为true。而这个也是导致工程编译很慢的罪魁祸首。那有没有什么办法可以保证，Android在Debug模式下即可以把JsBundle打进App应用内，而且在平时开发调试中页会很快的编译的完成呢？ 答案是一定可以的，我们接着去查看主Gradle引用的react.gradle脚本里的内容

import org.apache.tools.ant.taskdefs.condition.Os

def config = project.hasProperty("react") ? project.react : [];

def cliPath = config.cliPath ?: "node_modules/react-native/local-cli/cli.js"
def bundleAssetName = config.bundleAssetName ?: "index.android.bundle"
def entryFile = config.entryFile ?: "index.android.js"
def bundleCommand = config.bundleCommand ?: "bundle"

// because elvis operator
def elvisFile(thing) {
    return thing ? file(thing) : null;
}

def reactRoot = elvisFile(config.root) ?: file("../../")
def inputExcludes = config.inputExcludes ?: ["android/**", "ios/**"]
def bundleConfig = config.bundleConfig ? "${reactRoot}/${config.bundleConfig}" : null ;

void runBefore(String dependentTaskName, Task task) {
    Task dependentTask = tasks.findByPath(dependentTaskName);
    if (dependentTask != null) {
        dependentTask.dependsOn task
    }
}

gradle.projectsEvaluated {
    // Grab all build types and product flavors
    def buildTypes = android.buildTypes.collect { type -> type.name }
    def productFlavors = android.productFlavors.collect { flavor -> flavor.name }

    // When no product flavors defined, use empty
    if (!productFlavors) productFlavors.add('')

    productFlavors.each { productFlavorName ->
        buildTypes.each { buildTypeName ->
            // Create variant and target names
            def flavorNameCapitalized = "${productFlavorName.capitalize()}"
            def buildNameCapitalized = "${buildTypeName.capitalize()}"
            def targetName = "${flavorNameCapitalized}${buildNameCapitalized}"
            def targetPath = productFlavorName ?
                    "${productFlavorName}/${buildTypeName}" :
                    "${buildTypeName}"

            // React js bundle directories
            def jsBundleDirConfigName = "jsBundleDir${targetName}"
            def jsBundleDir = elvisFile(config."$jsBundleDirConfigName") ?:
                    file("$buildDir/intermediates/assets/${targetPath}")

            def resourcesDirConfigName = "resourcesDir${targetName}"
            def resourcesDir = elvisFile(config."${resourcesDirConfigName}") ?:
                    file("$buildDir/intermediates/res/merged/${targetPath}")
            def jsBundleFile = file("$jsBundleDir/$bundleAssetName")

            // Bundle task name for variant
            def bundleJsAndAssetsTaskName = "bundle${targetName}JsAndAssets"

            // Additional node and packager commandline arguments
            def nodeExecutableAndArgs = config.nodeExecutableAndArgs ?: ["node"]
            def extraPackagerArgs = config.extraPackagerArgs ?: []

            def currentBundleTask = tasks.create(
                    name: bundleJsAndAssetsTaskName,
                    type: Exec) {
                group = "react"
                description = "bundle JS and assets for ${targetName}."

                // Create dirs if they are not there (e.g. the "clean" task just ran)
                doFirst {
                    jsBundleDir.mkdirs()
                    resourcesDir.mkdirs()
                }

                // Set up inputs and outputs so gradle can cache the result
                inputs.files fileTree(dir: reactRoot, excludes: inputExcludes)
                outputs.dir jsBundleDir
                outputs.dir resourcesDir

                // Set up the call to the react-native cli
                workingDir reactRoot

                // Set up dev mode
                def devEnabled = !(config."devDisabledIn${targetName}"
                    || targetName.toLowerCase().contains("release"))

                def extraArgs = extraPackagerArgs;

                if (bundleConfig) {
                  extraArgs = extraArgs.clone()
                  extraArgs.add("--config");
                  extraArgs.add(bundleConfig);
                }

                if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                    commandLine("cmd", "/c", *nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                            "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
                } else {
                    commandLine(*nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                            "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
                }

                enabled config."bundleIn${targetName}" ||
                    config."bundleIn${buildTypeName.capitalize()}" ?:
                            targetName.toLowerCase().contains("release")
            }

            // Hook bundle${productFlavor}${buildType}JsAndAssets into the android build process
            currentBundleTask.dependsOn("merge${targetName}Resources")
            currentBundleTask.dependsOn("merge${targetName}Assets")

            runBefore("process${flavorNameCapitalized}Armeabi-v7a${buildNameCapitalized}Resources", currentBundleTask)
            runBefore("process${flavorNameCapitalized}X86${buildNameCapitalized}Resources", currentBundleTask)
            runBefore("processUniversal${targetName}Resources", currentBundleTask)
            runBefore("process${targetName}Resources", currentBundleTask)
            runBefore("dataBindingProcessLayouts${targetName}", currentBundleTask)
        }
    }
}

阅读以上gradle脚本可以发现，主要执行打包JsBundle的就是下面的这段脚本代码

    if (Os.isFamily(Os.FAMILY_WINDOWS)) {
        commandLine("cmd", "/c", *nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
        "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
    } else {
        commandLine(*nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
        "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
    }

而这段脚本是在被动态创建的Task任务里执行的

   def currentBundleTask = tasks.create(
                    name: bundleJsAndAssetsTaskName,
                    type: Exec) {
                group = "react"
                description = "bundle JS and assets for ${targetName}."

                // Create dirs if they are not there (e.g. the "clean" task just ran)
                doFirst {
                    jsBundleDir.mkdirs()
                    resourcesDir.mkdirs()
                }
                ......
                if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                    commandLine("cmd", "/c", *nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                            "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
                } else {
                    commandLine(*nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                            "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
                }
               ..........
               enabled isEnableBuildJsBundle(targetName) && (config."bundleIn${targetName}" ||
                    config."bundleIn${variant.buildType.name.capitalize()}" ?: targetName.toLowerCase().contains("release"))
   }

那么我们也就找到了优化的点，我们可以执行这个任务之前，打断这个Task的执行，不去调用JsBundle的脚本，从而也就节省了JSBundle的扫描编译时间，而这一部分的时间是相当可观的，至少有2Min！！！

二、优化代码的实现

（1）拷贝react.gradle到Android 工程主模块内，保持和主Gradle文件同级目录,如下图所示。

project.ext.react = [
        root         : "../..",
        bundleInDebug: true,
]
apply from: "react.gradle"

（3）新增isEnableBuildJsBundle方法

/**
 * 注释：是否开启编译JsBundle任务
 * 时间：2019/4/18 0018 10:18
 * 作者：郭翰林
 * @return
 */
boolean isEnableBuildJsBundle(String targetName) {
    if (targetName.toLowerCase().contains("release")) {
        return true
    }
    File jsBundle = file("$buildDir/intermediates/assets/debug/index.android.bundle")
    if (!jsBundle.exists()) {
        return true
    } else {
        println("【跳过编译JsBundle】JsBundle已存在,无需再次编译")
        return false
    }
}

（4）改写currentBundleTask()

          def currentBundleTask = tasks.create(
                name: "bundle${targetName}JsAndAssets",
                type: Exec) {
            group = "react"
            description = "bundle JS and assets for ${targetName}."

            .....................

            if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                commandLine("cmd", "/c", *nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                        "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
            } else {
                commandLine(*nodeExecutableAndArgs, cliPath, bundleCommand, "--platform", "android", "--dev", "${devEnabled}",
                        "--reset-cache", "--entry-file", entryFile, "--bundle-output", jsBundleFile, "--assets-dest", resourcesDir, *extraArgs)
            }

            enabled isEnableBuildJsBundle(targetName) && (config."bundleIn${targetName}" ||
                    config."bundleIn${variant.buildType.name.capitalize()}" ?: targetName.toLowerCase().contains("release"))
        }

最后看一下效果，Android工程增量编译的时间,基本都在1Min以内，可以用很快来形容！！！