cvc-complex-type.2.4.a: 发现了以元素 ‘base-extension‘ 开头的无效内容。应以 ‘{layoutlib}‘ 之一开头。

是 project 下的 build.gradle 中的 com.android.tools.build:gradle 版本太低的原因，我改成 3.5.2 后问题解决。

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.2'

        classpath 'com.github.dcendents:android-maven-gradle-plugin:1.4.1'
        classpath 'com.jfrog.bintray.gradle:gradle-bintray-plugin:1.7'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

ext {
    compileSdkVersion = 25
    buildToolsVersion = "28.0.3"

    targetSdkVersion = 25

    versionCode = 800800
    versionName = "0.8.8"
}

wrapper {
    gradleVersion = '2.14.1'
}