AS根目录下的 config.gradle 文件是用来 全局定义项目的配置信息（含compileSdkVersion、targetSdkVersion、versionCode、versionName、项目用到的公共依赖库）
写法示例：

ext {
    versionReleaseName = "1.0.00"
    android = [
            compileSdkVersion: 26,
            minSdkVersion    : 19,
            targetSdkVersion : 22,
            versionCode      : 13,
            versionName      : versionReleaseName
    ]
    appId = [
            "app": "com.newland.sft",
    ]
    supportV7Library = "26.1.0"
    dependencies = [
            "appcompat-v7"     : "com.android.support:appcompat-v7:${supportV7Library}",
            "support-v4"       : "com.android.support:support-v4:${supportV7Library}",
            "recyclerview-v7"  : "com.android.support:recyclerview-v7:${supportV7Library}",
            "design"           : "com.android.support:design:${supportV7Library}",
            "cardview"         : "com.android.support:cardview-v7:${supportV7Library}",
            "junit"            : "junit:junit:4.12",
            "runner"           : "com.android.support.test:runner:1.0.2",
            "espresso-core"    : "com.android.support.test.espresso:espresso-core:3.0.2",
            "constraint-layout": "com.android.support.constraint:constraint-layout:1.1.2",
            "logger": "com.orhanobut:logger:2.1.1",
            "gson": "com.google.code.gson:gson:2.8.2"
    ]
}

写好config.gradle文件后，需要到项目的根build.gradle文件里加上一句应用代码：

apply from: "config.gradle"
当有的模块需要用到公共配置文件config.gradle里面定义的信息，如三方依赖库，可以这样进行引用 ext闭包 ：

apply plugin: 'com.android.application'

def cfg = rootProject.ext.android    // 引用ext闭包
def appid = rootProject.ext.appId  // 引用ext中定义的appId字段
def dependLib = rootProject.ext.dependencies // 引用ext中定义的dependencies字段

android {
    compileSdkVersion cfg.compileSdkVersion
    defaultConfig {
        applicationId appid['app']
        minSdkVersion cfg.minSdkVersion
        targetSdkVersion cfg.targetSdkVersion
        versionCode cfg.versionCode
        versionName cfg.versionName
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    // 引用依赖库
    implementation dependLib['appcompat-v7']
    implementation dependLib['design']
    implementation dependLib['constraint-layout']
    testImplementation dependLib['junit']
    androidTestImplementation dependLib['runner']
    androidTestImplementation dependLib['espresso-core']
    implementation dependLib['logger']
    implementation project(':picker')
    implementation project(':command')
    implementation project(':b_bank_card')
    implementation project(':b_pos_tong')
    implementation project(':b_public')
}

    //定义签名
    signingConfigs {
        newland {
            keyAlias 'androiddebugkey'
            keyPassword 'android'
            storeFile file('../xxx.keystore')
            storePassword 'android'
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            //使用签名newland
            signingConfig signingConfigs.newland
        }
        debug {
            signingConfig signingConfigs.newland
        }
    }
    compileOptions {
        sourceCompatibility 1.8
        targetCompatibility 1.8
    }
}