所以我的同事推动了他们当地的。它破坏了一切。我复制了我的sdk路径从另一个应用程序，并做:

File -> Sync Project with Gradle Files

升级到最新的支持库后，我不得不升级到最新的Android studio(测试版)版本和gradle版本，然后IDE才能再次识别AppCompatActivity(无效缓存和重新启动没有做到这一点)

尝试温和的方法行不通，那就用强硬的方法吧: 退出当前Android Studio屏幕，转到项目的。idea文件夹，重命名库->lib_pre文件夹。

重新启动Android Studio。现在它将重新创建libraries文件夹并再次顺利工作。 Android Studio 3.1.3

所以我的同事推动了他们当地的。它破坏了一切。我复制了我的sdk路径从另一个应用程序，并做:

File -> Sync Project with Gradle Files

出现这种情况的原因如下:

你没有安装SDK API(这是我的问题) 你的项目/Android Studio不知道需要的文件在哪里 您的项目引用了不支持AppCompatActivity的过时编译版本 有个错别字

可能的解决方式:

Check your .gradle file to make sure you’re not referencing an outdated version. AppCompatActivity was added in version 25.1.0 and belongs to Maven artifact com.android.support:appcompat-v7:28.0.0-alpha1, so do not use any version earlier than this. In your build.gradle (Module: app) file you should have the dependency listed: dependencies { compile 'com.android.support:appcompat-v7:25.1.0' } You may be using a different version, but just make sure you have listed the dependency. Open the SDK manager and download every API 7 or newer. If you were missing the needed API it will fix that issue, and downloading all the newer API’s can save you some hassle later on as well. Check for typos in your import statement. Make sure it doesn’t say “AppCompactActivity” instead of “AppCompatActivity”. Resync your project (File >Sync project with Gradle files) Rebuild your project (Build >rebuild) Clean your project (Build >clean project) Close and restart Android Studio Update Android Studio Regenerate your libraries folder – In Android Studio, view your files in project view. Find the folder YourProjectName >.idea >libraries. Rename the folder to “libraries_delete_me”. Close and reopen Android Studio. Open your project again and the libraries folder should be regenerated with all of the files; you can now delete the “libraries_delete_me” folder.

如果通过gradle file / Invalidate caches和其他IDE工具的软方法不起作用，请使用硬方法:

退出Android Studio 在项目中导航到.idea文件夹 只需重命名libraries文件夹 重新启动Android Studio。现在它应该重新创建libraries文件夹并重新工作。

这对我很管用

Android Studio 3.1.2
Build #AI-173.4720617, built on April 13, 2018
JRE: 1.8.0_152-release-1024-b01 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Linux 4.13.0-38-generic

沙赫巴兹·阿里证实，这也行得通

Android Studio 3.1.3
Build #AI-173.4819257, built on June 4, 2018
JRE: 1.8.0_152-release-1024-b01 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Linux 4.13.0-38-generic

moujib确认，它可以在Android Studio 3.2.1上运行