在Mac上按“⌘+Shift+A”(在Windows上按“Ctrl+Shift+A”)，并在弹出的EditText中写入“将项目与Gradle文件同步”。然后双击出现的选项。然后它将同步您的Gradle文件SDK与项目文件。

我在Android Studio 4.0.1上得到这个错误。这是我的解决方案:去你的构建。gradle(Module: app)文件，然后更新compileSdkVersion和buildToolsVersion。

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.2"
}

在我的案例中，我为一个android项目下载了一个git库。该项目需要最低sdk版本21和目标sdk版本27。当我试图运行项目时，它给了我“请选择Android SDK错误”。我检查了我已经下载了所需的sdk文件。

对我来说，解决方案是“将项目与Gradle文件同步”

Source Compatibility should be selected as the minimum Android Version that your app should be compatible with(usually selected as SDK 15), Target Compatibility should be selected as the newest Android Version that your app should be compatible with(SDK 23). Afterwards you want to check your AndroidMenifest and your gradle.build to see if its realy set to the properties selected if not you can just add it manually. and ofcourse you should check the SDK Location is actually pointing to your android studio SDK folder (if you are importing from Eclipse then you should point to your Eclipse SDK folder).

Work for me 1文件>关闭投影。2打开一个现有的Android Studio项目

它帮助了我:

1. close project
2. remove .idea/ folder
3. select "import project (Gradle, Eclipse ADT, etc.)"

环境:

Android Studio 3.1.3
OS Macos High Sierra 10.13.5

另一个答案不适合我。