Could not get unknown property 'externalCompileSdkVersion'

报

Could not get unknown property 'externalCompileSdkVersion' for object of type com.android.build.gradle.LibraryExtension.

解决：

根目录的build.gradle

subprojects {
    project.evaluationDependsOn(':app')
}
ext {
    compileSdkVersion = 28
    buildToolsVersion '28.0.3'
    minSdkVersion 16
    targetSdkVersion 28
}


task clean(type: Delete) {
    delete rootProject.buildDir
}