方式一（推薦）

1.在根目錄下的build.gradle檔案下新增 ext{ …. } 中的內容

buildscript {

    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'

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

    }
}

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

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

ext{
    //SDK
    minSdkVersion = 15  
    targetSdkVersion = 26
    compileSdkVersion = 26

    //dependencies
    supportLibraryVersion ='26.1.0'
    butterknifeVersion = '8.8.1'
 

}

注：在android studio3.0之後，buildToolsVersion去掉了，等號也別忘記了，要不然會報： Gradle DSL method not found: ‘minSdkVersion()’

2.在app目錄下build.gradle中使用

apply plugin: 'com.android.application'

android {
    compileSdkVersion rootProject.ext.compileSdkVersion
    defaultConfig {
        applicationId "com.asialyf.zhiqu"
 

        minSdkVersion rootProject.ext.minSdkVersion
        targetSdkVersion rootProject.ext.targetSdkVersion
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "com.android.support:appcompat-v7:$rootProject.supportLibraryVersion"
    implementation "com.android.support:cardview-v7:$rootProject.supportLibraryVersion"
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'

    //Butterknife
    implementation "com.jakewharton:butterknife:$rootProject.butterknifeVersion"
}

注意：引用的依賴使用的是雙引號

方式二

1.在專案根目錄下建立.gradle檔案，如：config.gradle
2.在根目錄下的build.gradle檔案中引入建立的配置檔案
apply from:”config.gradle”
3.最後config.gradle中檔案內容可以自己定義

ext {  
    // 用於編譯的SDK版本  
    COMPILE_SDK_VERSION = 23  

    // 用於Gradle編譯專案的工具版本  
    BUILD_TOOLS_VERSION = "24.0.2"  

    // 最低支援Android版本  
    MIN_SDK_VERSION = 14  

    // 目標版本  
    TARGET_SDK_VERSION = 23  

    APPCOMPAT_VERSION = '23.2.1'  

} 

4.在app目錄下的build.gradle中使用

dependencies {  
    compile fileTree(include: ['*.jar'], dir: 'libs')  
    compile "com.android.support:cardview-v7:${APPCOMPAT_VERSION}"  
    compile "com.android.support:appcompat-v7:${APPCOMPAT_VERSION}"  
    compile "com.android.support:design:${APPCOMPAT_VERSION}"  
    compile 'com.github.bumptech.glide:glide:3.7.0'  
}