今天，写好Demo兴致勃勃准备打个Jar包在Unity中测试下，不料，突然出现AGPBI这个异常，日志如下：
AGPBI: {"kind":"error","text":"Program type already present: android.support.v4.app.BackStackRecord$Op","sources":[{}],"tool":"D8"}
:app:transformClassesWithDexBuilderForDebug UP-TO-DATE
AGPBI: {"kind":"error","text":"Program type already present: android.support.v4.app.BackStackRecord$Op","sources":[{}],"tool":"D8"}
:app:transformDexArchiveWithExternalLibsDexMergerForDebug FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives: E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\0.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\1.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\2.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\3.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\4.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\5.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\6.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\7.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\8.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\9.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\10.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\11.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\12.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\13.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\14.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\15.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\16.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\17.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\18.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\19.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\20.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\21.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\22.jar, E:\AiYouDemo\UcenterSdkTest\app\build\intermediates\transforms\dexBuilder\debug\23.jar
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BUILD FAILED in 0s
20 actionable tasks: 1 executed, 19 up-to-date
10:36:12: Task execution finished 'exportJar'.
网上搜索，发现很多人都说包重复引用导致，但是LZ这是一个简单得Demo，并没有依赖太多项，况且，有的小伙伴说，需要分包，LZ瞬间很是不解，毛都没，分个啥？
随后，果断检查代码，查看是不是由于疏忽导致这种问题，果然：
打包时，LZ忘记将application：
apply plugin: ‘com.android.application’
修改为library：
apply plugin: ‘com.android.library’
实属尴尬啊~
