1. 下载Android SDK：通过下载Android Studio进行安装，但是下载Android Studio 3.6.1版本后，SDK Manage有变化。Unity打包需要的SDK Tools被Obsolete了，需要把Hide Obsolete Packages的勾选去掉才能看到。
2. 安装SDK Build-Tools 30-rc1之后，/Users/xxx/Library/Android/sdk/build-tools目录下，30-rc1的目录名称是30.0.0-rc1，会导致Unity打包会报错。
CommandInvokationFailure: Gradle build failed.
/Library/Java/JavaVirtualMachines/jdk1.8.0_241.jdk/Contents/Home/bin/java -classpath "/Users/jerryqin/Desktop/KH/Unity17EditorApp/MacEditor/PlaybackEngines/AndroidPlayer/Tools/gradle/lib/gradle-launcher-4.6.jar" org.gradle.launcher.GradleMain "-Dorg.gradle.jvmargs=-Xmx4096m" "assembleRelease"stderr[
FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring root project 'gradleOut'.
> Failed to find Build Tools revision 30.0.0* 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 3s
]
stdout[]
exit code: 1
UnityEditor.Android.Command.WaitForProgramToRun (UnityEditor.Utils.Program p, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg)
UnityEditor.Android.Command.Run (System.Diagnostics.ProcessStartInfo psi, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg)
UnityEditor.Android.AndroidJavaTools.RunJava (System.String args, System.String workingdir, System.Action`1 progress, System.String error)
UnityEditor.Android.GradleWrapper.Run (System.String workingdir, System.String task, System.Action`1 progress)
Rethrow as GradleInvokationException: Gradle build failed
UnityEditor.Android.GradleWrapper.Run (System.String workingdir, System.String task, System.Action`1 progress)
UnityEditor.Android.PostProcessor.Tasks.BuildGradleProject.Execute (UnityEditor.Android.PostProcessor.PostProcessorContext context)
UnityEditor.Android.PostProcessor.PostProcessRunner.RunAllTasks (UnityEditor.Android.PostProcessor.PostProcessorContext context)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
有两种解决方法：
解决方法1：把 30.0.0-rc1 目录改名为 30.0.0就可以
解决方法2：修改 Unity安装目录下的文件 /PlaybackEngines/AndroidPlayer/Tools/GradleTemplates/mainTemplate.gradle，改成其他版本的。
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