在Unity还是4.x 5.x的时代，为了做一些安卓原生功能，如获取电量，wifi信号强度等功能，或者是为了接入某些原生SDK，经常需要制作Unity的Android原生插件，当时基本就是基于Unity的安卓classes.jar制作plugin.jar，然后自定义AndroidManifest.xml，一起放到Unity项目的Assets/Plugins/Android下，然后Build安卓apk即可，简单粗暴。最近又有了做安卓插件的需求，这次换上了2020版的Unity，本以为还是当年熟悉的操作，没成想来了个大人，时代变了，踩了不少新坑：
首先，当年好像还是用Eclipse做Android开发，现在早就是Android Studio的天下了，我用的版本是：Chipmunk 2021.2.1 Patch 2，按着网上找到的教程（对，很久没用了，都快忘了怎么建项目了），创建了Android Library项目，又从Unity的“D:\Program Files\Unity\Hub\Editor\2020.3.30f1c1\Editor\Data\PlaybackEngines\AndroidPlayer\Variations\mono\Release\Classes”位置，拿到了熟悉的classes.jar，注意这里有一些变量，比如mono，现在还有了il2cpp的选择，Release对应还有Debug，根据实际情况进行选择吧。然后，随便写了几个简单的静态方法，Unity C#里调用了下，nice，没有问题，于是开始进行下一步，自定义入口activity，然后就开始踩坑了：
按照之前的经验，自定义入口activity的操作，基本就是写个activity类，然后extends UnityPlayerActivity，然后再自己写个AndroidManifest.xml，指定自己的activity为启动入口，这些基本也是Unity官方文档上有说明的：https://docs.unity3d.com/2020.3/Documentation/Manual/AndroidUnityPlayerActivity.html ，一通操作过后，神奇的发现Unity 2020的classes.jar中居然import不到UnityPlayerActivity了，导致插件库编译报错，于是找到了这个参考：Unity Android 重写UnityPlayerActivity https://zhuanlan.zhihu.com/p/451547547 ，文中提到，Unity 2019.3之后classes.jar中就不再包含原版入口activity类了，不明觉厉，于是又顺利在“D:\Program Files\Unity\Hub\Editor\2020.3.30f1c1\Editor\Data\PlaybackEngines\AndroidPlayer\Source\com\unity3d\player”找到了UnityPlayerActivity.java这个文件，看来是直接把源码扔出来了，放进Android Studio项目里，这下编译构建ok了，拿着输出的aar（对，这个也是新的，以前就是出个jar就行了，unity官方文档上也提到过这个，也不什么时候开始Android Studio的库项目就出的是aar了，其实就是原来的jar加上各种资源、jni库等，理应是更方便了吧），AndroidManifest.xml，放到Unity项目里，结果Build时报了这个错：
注: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\src\main\java\com\unity3d\player\UnityPlayerActivity.java使用或覆盖了已过时的 API。
注: 有关详细信息, 请使用 -Xlint:deprecation 重新编译。
D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex: D8: Type com.unity3d.player.UnityPlayerActivity is defined multiple times: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex, D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\launcher\build\intermediates\external_libs_dex\debug\mergeExtDexDebug\classes.dex
com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives:
Type com.unity3d.player.UnityPlayerActivity is defined multiple times: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex, D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\launcher\build\intermediates\external_libs_dex\debug\mergeExtDexDebug\classes.dex
Learn how to resolve the issue at https://developer.android.com/studio/build/dependencies#duplicate_classes.
at com.android.builder.dexing.D8DexArchiveMerger.getExceptionToRethrow(D8DexArchiveMerger.java:132)
at com.android.builder.dexing.D8DexArchiveMerger.mergeDexArchives(D8DexArchiveMerger.java:119)
at com.android.build.gradle.internal.transforms.DexMergerTransformCallable.call(DexMergerTransformCallable.java:102)
at com.android.build.gradle.internal.tasks.DexMergingTaskRunnable.run(DexMergingTask.kt:441)
at com.android.build.gradle.internal.tasks.Workers$ActionFacade.run(Workers.kt:242)
at org.gradle.workers.internal.AdapterWorkAction.execute(AdapterWorkAction.java:50)
at org.gradle.workers.internal.DefaultWorkerServer.execute(DefaultWorkerServer.java:50)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:63)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:59)
at org.gradle.internal.classloader.ClassLoaderUtils.executeInClassloader(ClassLoaderUtils.java:98)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1.lambda$execute$0(NoIsolationWorkerFactory.java:59)
at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:44)
at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:41)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:416)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406)
at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102)
at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36)
at org.gradle.workers.internal.AbstractWorker.executeWrappedInBuildOperation(AbstractWorker.java:41)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1.execute(NoIsolationWorkerFactory.java:53)
at org.gradle.workers.internal.DefaultWorkerExecutor.lambda$submitWork$2(DefaultWorkerExecutor.java:200)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runExecution(DefaultConditionalExecutionQueue.java:215)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runBatch(DefaultConditionalExecutionQueue.java:164)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.run(DefaultConditionalExecutionQueue.java:131)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
at java.lang.Thread.run(Thread.java:748)
Caused by: com.android.tools.r8.CompilationFailedException: Compilation failed to complete
at com.android.tools.r8.utils.W.a(:87)
at com.android.tools.r8.D8.run(:11)
at com.android.builder.dexing.D8DexArchiveMerger.mergeDexArchives(D8DexArchiveMerger.java:117)
... 33 more
Caused by: com.android.tools.r8.utils.b: Error: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex, Type com.unity3d.player.UnityPlayerActivity is defined multiple times: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex, D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\launcher\build\intermediates\external_libs_dex\debug\mergeExtDexDebug\classes.dex
at Version.fakeStackEntry(Version_2.0.88.java:0)
at com.android.tools.r8.utils.O0.a(:21)
at com.android.tools.r8.utils.N0.b(:7)
at com.android.tools.r8.utils.N0.a(:27)
at com.android.tools.r8.utils.N0.a(:10)
at java.util.concurrent.ConcurrentHashMap.merge(ConcurrentHashMap.java:1990)
at com.android.tools.r8.utils.N0.a(:6)
at com.android.tools.r8.graph.D0$c.f(:3)
at com.android.tools.r8.dex.a.a(:83)
at com.android.tools.r8.dex.a.a(:10)
at com.android.tools.r8.D8.d(:6)
at com.android.tools.r8.D8.b(:1)
at com.android.tools.r8.utils.W.a(:30)
... 35 more
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':launcher:mergeDexDebug'.
> A failure occurred while executing com.android.build.gradle.internal.tasks.Workers$ActionFacade
> com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives:
Type com.unity3d.player.UnityPlayerActivity is defined multiple times: D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\unityLibrary\build\.transforms\17536f9632ccf2b42cf1f00304f1b9b6\classes\classes.dex, D:\Projects\Unity2020\pw_iot2\Temp\gradleOut\launcher\build\intermediates\external_libs_dex\debug\mergeExtDexDebug\classes.dex
Learn how to resolve the issue at https://developer.android.com/studio/build/dependencies#duplicate_classes.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 23s
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)
大致看了一下，就明白怎么回事了，原来的UnityPlayerActivity在classes.jar里，以.class形式存在，然后呢，我们的库项目只是使用classes.jar作为引用库编译，最终Unity构建整个apk时还会加上实际的classes.jar一起编译，而把UnityPlayerActivity.java放进我们的项目里，生成的插件aar中的jar里便会包含一份UnityPlayerActivity.class，这时Unity最终构建apk时这个class就会重复定义报错！解决的方法嘛，可以按照上面的参考知乎里提到的手动删jar里的class，再重新打包，我目前的做法是将UnityPlayerActivity改个名，比如OriginalUnityPlayerActivity，然后再extends，或者还看到网上有说把UnityPlayerActivity先打个库jar包，然后和classes.jar一起“compileOnly files(‘libs/unity-activity.jar’)”引用，虽然有点麻烦，但理论上可行，又或者按Unity官方文档里提到的方法，干脆直接改这个.java。
不过这几种做法感觉都不是那么的“优雅”，而且官方文档里也没提到现在这种应该是挺大众的做法下，怎么解决重复定义问题，本来我想研究下gradle脚本操作，看能不能自定义下jar包的打包逻辑，排除指定.class文件，无奈gradle实在太复杂，试了半天也没成功，先这样临时解决下，以后有时间再研究更加“优雅”的处理方法吧。
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