组成
AS一个项目中可以有多个模块。build.gradle也就由两个层级组成，项目根目录的build.gradle配置所有模块公用的需求。模块build.gradle配置仅模块需要的。
项目根目录build.gradle
基本组成
/**
* The buildscript block is where you configure the repositories and
* dependencies for Gradle itself—meaning, you should not include dependencies
* for your modules here. For example, this block includes the Android plugin for
* Gradle as a dependency because it provides the additional instructions Gradle
* needs to build Android app modules.
*/
// 配置gradle相关依赖，用来编译。
buildscript {
/**
* The repositories block configures the repositories Gradle uses to
* search or download the dependencies. Gradle pre-configures support for remote
* repositories such as JCenter, Maven Central, and Ivy. You can also use local
* repositories or define your own remote repositories. The code below defines
* JCenter as the repository Gradle should use to look for its dependencies.
*
* New projects created using Android Studio 3.0 and higher also include
* Google's Maven repository.
*/
// 配置编译项目，gradle下载依赖的资源的仓库。资源库可以是本地的，也可以是自定义的远端库。
repositories {
google()
jcenter()
}
/**
* The dependencies block configures the dependencies Gradle needs to use
* to build your project. The following line adds Android plugin for Gradle
* version 3.3.2 as a classpath dependency.
*/
// 配置gradle编译项目需要依赖的工具，如com.android.tools.build、gradle:3.3.2
dependencies {
classpath 'com.android.tools.build:gradle:3.3.2'
}
}
/**
* The allprojects block is where you configure the repositories and
* dependencies used by all modules in your project, such as third-party plugins
* or libraries. However, you should configure module-specific dependencies in
* each module-level build.gradle file. For new projects, Android Studio
* includes JCenter and Google's Maven repository by default, but it does not
* configure any dependencies (unless you select a template that requires some).
*/
// 配置项目所有模块依赖的第三方插件或者库。依赖文件库可以是本地的，也可以是自定义的远端库
allprojects {
repositories {
google()
jcenter()
}
}
配置项目范围的属性
对于包含多个模块的 Android 项目，在项目级别定义某些属性，并在所有模块间共享这些属性可能会非常有用。 为此可以将 额外属性 添加到顶级 build.gradle 文件的 ext 代码块中。
buildscript {...}
allprojects {...}
// This block encapsulates custom properties and makes them available to all
// modules in the project.
ext {
// The following are only a few examples of the types of properties you can define.
compileSdkVersion = 28
// You can also create properties to specify versions for dependencies.
// Having consistent versions between modules can avoid conflicts with behavior.
supportLibVersion = "28.0.0"
...
}
...
要从相同项目中的模块访问这些属性，请在模块的 build.gradle 文件（您可以在以下部分了解有关此文件的详细信息）中使用以下语法。
android {
// Use the following syntax to access properties you defined at the project level:
// rootProject.ext.property_name
compileSdkVersion rootProject.ext.compileSdkVersion
...
}
...
dependencies {
implementation "com.android.support:appcompat-v7:${rootProject.ext.supportLibVersion}"
...
}
额外属性
在gradle可以使用自定义的额外属性，比如：projects, tasks, and source sets。额外属性可以被add、read或者通过ext属性定义。一个ext块中至少可以定义一个属性。
plugins {
id 'java'
}
ext {
springVersion = "3.1.0.RELEASE"
emailNotification = "[email protected]"
}
sourceSets.all { ext.purpose = null }
sourceSets {
main {
purpose = "production"
}
test {
purpose = "test"
}
plugin {
purpose = "production"
}
}
task printProperties {
doLast {
println springVersion
println emailNotification
sourceSets.matching { it.purpose == "production" }.each { println it.name }
}
}
Output of gradle -q printProperties
> gradle -q printProperties
3.1.0.RELEASE
[email protected]
main
plugin
参考资料
Android官网文档：https://developer.android.google.cn/studio/build
深入学习自定义属性：https://docs.gradle.org/current/userguide/writing_build_scripts.html#sec:extra_properties 学习Extra properties节。
Android build中使用gradle：参照https://google.github.io/android-gradle-dsl/current/index.html
全面学习gradle：https://gradle.org/guides/#getting-started
模块级构建文件
模块级 build.gradle 文件位于各 project/module/ 目录中，用于配置适用于其所在模块的构建设置。 可以通过配置这些构建设置来提供自定义打包选项（例如附加构建类型和产品风格），以及替换 main/ 应用清单或顶级 build.gradle 文件中的设置。
此 Android 应用模块 build.gradle 文件示例概括了应了解的某些基本 DSL 元素和设置。
/**
* The first line in the build configuration applies the Android plugin for
* Gradle to this build and makes the android block available to specify
* Android-specific build options.
*/
// 告诉gradle编译该模块需要的Android插件，使后面的android块可以访问特定的编译选项
apply plugin: 'com.android.application'
/**
* The android block is where you configure all your Android-specific
* build options.
*/
// 配置Android编译选项
android {
/**
* compileSdkVersion specifies the Android API level Gradle should use to
* compile your app. This means your app can use the API features included in
* this API level and lower.
*/
compileSdkVersion 28
/**
* buildToolsVersion specifies the version of the SDK build tools, command-line
* utilities, and compiler that Gradle should use to build your app. You need to
* download the build tools using the SDK Manager.
*
* This property is optional because the plugin uses a recommended version of
* the build tools by default.
*/
buildToolsVersion "28.0.3"
/**
* The defaultConfig block encapsulates default settings and entries for all
* build variants, and can override some attributes in main/AndroidManifest.xml
* dynamically from the build system. You can configure product flavors to override
* these values for different versions of your app.
*/
defaultConfig {
/**
* applicationId uniquely identifies the package for publishing.
* However, your source code should still reference the package name
* defined by the package attribute in the main/AndroidManifest.xml file.
*/
applicationId 'com.example.myapp'
// Defines the minimum API level required to run the app.
minSdkVersion 15
// Specifies the API level used to test the app.
targetSdkVersion 28
// Defines the version number of your app.
versionCode 1
// Defines a user-friendly version name for your app.
versionName "1.0"
}
/**
* The buildTypes block is where you can configure multiple build types.
* By default, the build system defines two build types: debug and release. The
* debug build type is not explicitly shown in the default build configuration,
* but it includes debugging tools and is signed with the debug key. The release
* build type applies Proguard settings and is not signed by default.
*/
buildTypes {
/**
* By default, Android Studio configures the release build type to enable code
* shrinking, using minifyEnabled, and specifies the Proguard settings file.
*/
release {
minifyEnabled true // Enables code shrinking for the release build type.
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
/**
* The productFlavors block is where you can configure multiple product flavors.
* This allows you to create different versions of your app that can
* override the defaultConfig block with their own settings. Product flavors
* are optional, and the build system does not create them by default.
*
* This example creates a free and paid product flavor. Each product flavor
* then specifies its own application ID, so that they can exist on the Google
* Play Store, or an Android device, simultaneously.
*
* If you declare product flavors, you must also declare flavor dimensions
* and assign each flavor to a flavor dimension.
*/
// 配置编译出不同特色的产品，如收费版、免费版；可选配置，无默认配置
flavorDimensions "tier"
productFlavors {
free {
dimension "tier"
applicationId 'com.example.myapp.free'
}
paid {
dimension "tier"
applicationId 'com.example.myapp.paid'
}
}
/**
* The splits block is where you can configure different APK builds that
* each contain only code and resources for a supported screen density or
* ABI. You'll also need to configure your build so that each APK has a
* different versionCode.
*/
// apk切分规则。如下：使不同分辨率设备使用对应的apk，配置编译出和设备分辨率相同的apk，减小apk大小，节省设备空间
splits {
// Settings to build multiple APKs based on screen density.
density {
// Enable or disable building multiple APKs.
enable false
// Exclude these densities when building multiple APKs.
exclude "ldpi", "tvdpi", "xxxhdpi", "400dpi", "560dpi"
}
}
}
/**
* The dependencies block in the module-level build configuration file
* specifies dependencies required to build only the module itself.
* To learn more, go to Add build dependencies.
*/
// 设置模块级别的依赖
dependencies {
implementation project(":lib")
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation fileTree(dir: 'libs', include: ['*.jar'])
}