APTTransform实现多模块应用Application生命周期分发

　　前言
　　组件化开发过程中，各个模块内往往需要感知Application的生命周期，以获取context完成初始化工作等，业务上模块间或存在初始化顺序要求，比较常规的做法有：
　　在common模块定义   AppLifecycleCallback  interface AppLifecycleCallback {    fun getPriority(): Int = 0    fun onCreate(context: Context)}复制代码
　　各个模块实现   AppLifecycleCallback   ，如Home模块  class HomeAppLifecycle : AppLifecycleCallback {    override fun getPriority(): Int = 0        override fun onCreate(context: Context) {        //todo    }}复制代码
　　然后在   MainApplication   中实现生命周期分发  class MainApplication : Application() {    private val callbacks = mutableListOf()        override fun onCreate() {        super.onCreate()        callbacks.add(HomeAppLifecycle())        callbacks.add(UserAppLifecycle())        // add whatever you want        // 排序实现模块顺序分发        callbacks.sortBy { it.getPriority() }        callbacks.forEach { it.onCreate(this) }    }    }复制代码
　　这样能实现需求，但每增加一个模块，就得回到MainApplication中添加一个，不够优雅不够装，这时候就可以用上   APT + Transform  实现原理各模块创建AppLifecycleCallback实现类，添加注解，apt为其生成代理类，以＂_Proxy＂结尾  构造   AppLifecycleManager   对外API，统一管理Proxyc allbacks  gradle transform遍历.class文件，找到＂_Proxy＂的所有类，保存类路径，使用   asm   将代理类＂加入＂到AppLifecycleManager中
　　此方案主要是为了解学习apt，gradle transform，实际上有更好的实现方案。各位大佬畅所欲言，提出此方案的短板  实现过程一、 AppLifecycle API
　　创建android-library，定义   AppLifecycleCallback   、   AppLifecycleManager
　　interface AppLifecycleCallback {    fun getPriority(): Int = 0    fun onCreate(context: Context)}复制代码
　　AppLifecycleManager中   onCreate   是对外的API，在MainAppkication中调用；   registerAppLifecycleCallback   则是在transform阶段使用asm在AppLifecycleManager的构造方法中调用，将代理类路径传入，最终通过反射存储在callbacks中  object AppLifecycleManager {    private var callbacks: MutableList? = null    fun onCreate(context: Context) {        callbacks?.run {            sortBy { it.getPriority() }            forEach { it.onCreate(context) }        }    }    private fun registerAppLifecycleCallback(name: String) {        try {            if (callbacks == null) {                callbacks = mutableListOf()            }            val instance = Class.forName(name).getConstructor().newInstance()            if (instance is AppLifecycleCallback && !callbacks!!.contains(instance)) {                callbacks!!.add(instance)            }        } catch (e: Exception) {            e.printStackTrace()        }    }}复制代码二、 APT创建kotlin-library，定义annotation
　　@Target(AnnotationTarget.CLASS)@Retention(AnnotationRetention.SOURCE)annotation class AppLifecycle()复制代码创建kotlin-library，定义Processor，获取所有 @AppLifecycle注解类，使用   KotlinPoet   生成Proxy类
　　@AutoService(Processor::class)class AppLifecycleProcessor : AbstractProcessor() {    // 省略部分代码    override fun process(p0: MutableSet?, environment: RoundEnvironment?): Boolean {        environment?.run {            getElementsAnnotatedWith(AppLifecycle::class.java)                .filter { it.kind == ElementKind.CLASS }                .filter {                    (it as TypeElement).interfaces.contains(                        elements.getTypeElement(callbackName).asType()                    )                }                .forEach {                    AppLifecycleProxyBuilder(it as TypeElement, elements).build().writeTo(filer)                }        }        return true    }}复制代码
　　KotlinPoet生成Proxy类  class AppLifecycleProxyBuilder(private val typeElement: TypeElement, elements: Elements) {    // 省略部分代码    fun build(): FileSpec {        return FileSpec.builder(packageName, fileName)            .addType(getTypeSpec())            .build()    }    private fun getTypeSpec(): TypeSpec {        return TypeSpec.classBuilder(fileName)            .addProperty(getProperty())            .addSuperinterface(superInterface)            .addFunction(getOnCreate())            .addFunction(getPriority())            .build()    }    private fun getProperty(): PropertySpec {        // 对应注解类实例        return PropertySpec.builder(＂callback＂, typeElement.asClassName(), KModifier.PRIVATE)            .initializer(＂%T()＂, typeElement.asType())            .build()    }    private fun getOnCreate(): FunSpec {        // onCreate(context: Context)        return FunSpec.builder(＂onCreate＂)            .addModifiers(KModifier.OVERRIDE)            .addParameter(＂context＂, contextType)            .addStatement(＂callback.onCreate(context)＂)            .build()    }    private fun getPriority(): FunSpec {        // getPriority(): Int        return FunSpec.builder(＂getPriority＂)            .addModifiers(KModifier.OVERRIDE)            .returns(Int::class)            .addStatement(＂return callback.getPriority()＂)            .build()    }}复制代码
　　注：kotlin使用apt，要在build.gradle要有以下两个声明  plugins {    id ＂kotlin-kapt＂}dependencies {    kapt (project(＂:processor＂))}复制代码三、 Gradle Transform
　　创建kotlin-library
　　定义AppLifecyclePlugin，继承Transform，实现Project接口  class AppLifecyclePlugin : Transform(), Plugin {    private val appLifecycleClassNames = mutableListOf()    private var appLifecyclesJar:File? = null        override fun transform(transformInvocation: TransformInvocation?) {        // transform中遍历.class文件，类名以＂_Proxy＂结尾并且实现AppLifecycleCallback        ...        if (name.endsWith(proxySuffix) && classReader.interfaces.contains(callbackInfo)) {            appLifecycleClassNames.add(name)        }        ...        // 定位到包含 ApplifecycleManager的JarEntry        if(jarEntity.name == managerClassFile){            appLifecyclesJar = outputJar        }        // 最终使用ClassVistor将所有Proxy类加入到Manager中的callbacks里        val cv: ClassVisitor = AppLifecycleVisitor(classWriter,appLifecycleClassNames)        classReader.accept(cv, ClassReader.EXPAND_FRAMES)        classWriter.toByteArray()    }}复制代码
　　AppLifecycleVisitor  class AppLifecycleVisitor(classVisitor: ClassVisitor,private val callbacks: List) : ClassVisitor(Opcodes.ASM9,classVisitor) {    override fun visitMethod(        access: Int,        name: String?,        descriptor: String?,        signature: String?,        exceptions: Array?    ): MethodVisitor {        var visitor = super.visitMethod(access, name, descriptor, signature, exceptions)        if (＂＂ == name && ＂()V＂ == descriptor && access and Opcodes.ACC_PRIVATE != 0) {            visitor = object : AdviceAdapter(ASM9, visitor, access, name, descriptor) {                override fun onMethodExit(opcode: Int) {                    for (item in callbacks) {                        mv.visitVarInsn(ALOAD, 0)                        mv.visitLdcInsn(item.replace(＂/＂, ＂.＂))                        mv.visitMethodInsn(                            INVOKESPECIAL,                            ＂com/lauter/applifecycle/AppLifecycleManager＂,                            ＂registerAppLifecycleCallback＂,                            ＂(Ljava/lang/String;)V＂,                            false                        )                    }                }            }        }        return visitor    }}复制代码
　　创建完AppLifecyclePlugin，创建文件src/main/resources/META-INF/gradle-plugins/lauter.applifecycle.properties  implementation-class=com.lauter.applifecycle.AppLifecyclePlugin复制代码
　　到此，工作基本完成。只需要将plugin发布到本地，就可以测试功能了  四、 发布测试
　　在上文创建的plugin项目下build.gradle中添加：  plugins {    ...    // 添加publish    id ＂maven-publish＂}...// 发布到本地publishing {    publications {        mavenJava(MavenPublication) {            from components.java            groupId = ＂io.github.chenlauter＂            artifactId = ＂applifecycle＂            version = ＂1.0＂        }    }    repositories {        mavenLocal()        maven {            url = ＂../local-plugin-repository＂        }    }}复制代码
　　在gradle中执行publish，发布完成后项目中会新增   local-plugin-repository   文件夹
　　在project的build.gradle中添加依赖  buildscript {    repositories {        ...        // 添加依赖，gradle7.1之后是到setting.gralde-pluginManagement中添加        maven { url ＂./local-plugin-repository＂ }    }    dependencies {        ...        classpath(＂io.github.chenlauter:applifecycle:1.0＂)    }}复制代码
　　最后在app的build.gradle中添加  plugins {    ...    // 这里跟第三步创建的lauter.applifecycle.properties文件名对应    id ＂lauter.applifecycle＂}复制代码
　　至此，所以依赖都配置完毕，运行工程，在app-build下，用Android Studio直接打开apk查看 AppLifecycleManager的字节码，可以看到，在构造方法中已加入两个Proxy类路径调用：
　　通过查看日志打印，也能看到功能正常  D/AppLifecycle: HomeAppLifecycle onCreate D/AppLifecycle: MainAppLifecycle onCreate复制代码项目地址
　　github.com/ChenLauter/…  启发参考
　　juejin.cn/post/702921…
　　原文链接：https://juejin.cn/post/7126419784471674887