Cannot get property 'compileSdkVersion' on extra properties extension as it does not exit

报错为：Error:(9, 0) Cannot get property 'compileSdkVersion' on extra properties extension as it does not exist

<a href="openFile:D:\zyl\projects\7 doing\DroidPluginDemo\DroidPlugin\build.gradle">Open File</a>

解决方法:在Buid.gradle(project:XXX) 中根目录添加

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.2'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

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

//添加此处 解决rootProject.ext.compileSdkVersion 不存在的问题
ext {
    compileSdkVersion = 26
    buildToolsVersion = "25.0.3"
    minSdkVersion = 15
    targetSdkVersion = 26
}