Android Studio 工程目录下各个文件的作用

不创造知识，我只是知识的搬运工。本篇文章照抄https://developer.android.com/studio/build/#build-config，建议直接点击链接

下面的工程目录示意图

1. settings.gradle文件位于项目根目录，用于指示Gradle在构建应用时应将哪些模块包括在内。对大多数项目而言，该文件很简单，只包括以下内容

include ‘:app’

不过，多模块项目需要指定应包括在最终构建之中的每个模块。

2.顶级 build.gradle文件位于项目根目录，用于定义适用于项目中所有模块的构建配置。默认情况下，这个顶级构建文件使用buildscript()代码块来定义项目中所有模块共用的Gradle存储区和依赖项。以下代码示例描述和默认设置和DSL元素可以在新建项目后的顶级buile.gradle文件中找到

/**
 * 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.
 * buildscript {}块是您为Gradle本身配置存储库和依赖项的地方 - 这意味着，您不应在此处包含模块的依赖项。
 * 例如，此块包含Gradle 的Android插件作为依赖项，因为它提供了Gradle构建Android应用程序模块所需的其他指令。
 */
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.
     */

    repositories {
        jcenter()
    }

    /**
     * The dependencies {} block configures the dependencies Gradle needs to use
     * to build your project. The following line adds Android Plugin for Gradle
     * version 3.2.1 as a classpath dependency.
     */

    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
    }
}

/**
 * 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. Dependencies that are not required by all the modules in the
 * project should be configured in module-level build.gradle files. For new
 * projects, Android Studio configures JCenter as the default repository, but it
 * does not configure any dependencies.
 */

allprojects {
   repositories {
       jcenter()
   }
}

3. 模块级build.gridle文件位于每个//目录下，用于配置适用于其所在模块的构建设置，您可以通过配置这些构建设置来提供自定义打包选项，以及替换，main/应用清单或顶级build.gridle文件中的设置。

以下的实例Android应用模块build.gradle文件概述了您应该了解的部分基本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.
 */

apply plugin: 'com.android.application'

/**
 * The android {} block is where you configure all your Android-specific
 * build options.
 */

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.
   *
   * 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.
   */

  compileSdkVersion 28
  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 defaultConfig {} 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.
   */

  productFlavors {
    free {
      applicationId 'com.example.myapp.free'
    }

    paid {
      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.
   */

  splits {
    // Screen density split settings
    density {

      // Enable or disable the density split mechanism
      enable false

      // Exclude these densities from splits
      exclude "ldpi", "tvdpi", "xxxhdpi", "400dpi", "560dpi"
    }
  }
}

/**
 * The dependencies {} block in the module-level build configuration file
 * only specifies dependencies required to build the module itself.
 */

dependencies {
    compile project(":lib")
    compile 'com.android.support:appcompat-v7:28.0.0'
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

4. Gradle属性文件，Gradle还包含两个属性文件，位于项目根目录，可用于指定适用于Gradle构建工具包本身的设置。

gradle.properties,你可以在其中配置项目范围Gradle设置，例如Gradle后台进程最大堆大小。

local.properties,为构建系统配置本地环境属性，例如SDK安装路径。该文件的内容由Android Studio自动生成并且专用于

本地开发环境，因此你不应该手动修改该文件，或将其纳入你的版本控制系统。

5. 源集

Android studio 按照逻辑关系将每个模块的源代码和资源分组为源集。模块的main/源集包括其所有构建变体共用的代码

和资源。其他源集目录为可选项，在您配置新的构建变体时，Android Studio不会自动为您创建这些目录。不过，创建类似于main/的源集有助于让Gradle只在构建特定应用版本时使用的文件和资源井然有序。

src/main/此源集包括所有构建变体共用的代码资源

src/创建此源集可以加入特定构建类型专用的代码和资源

src/创建此源集可加入特定产品风味专用的代码和资源

src/创建此源集可加入特定构建变体专用的代码和资源

例如，要生成应用的“完整调试”版本，构建系统需要合并来自以下源集的代码、设置和资源：

• src/fullDebug/（构建变体源集）
• src/debug/（构建类型源集） 类型：表示是正式版本还是测试版本
• src/full/（产品风味源集） 风味：表示不同的版本的应用
• src/main/（主源集）

如果不同源集包含同一文件的不同版本，Gradle 将按以下优先顺序决定使用哪一个文件（左侧源集替换右侧源集的文件和设置）：构建变体 > 构建类型 > 产品风味 > 主源集 > 库依赖项

这样一来，Gradle 便可使用专用于您试图构建的构建变体的文件，同时对与其他应用版本共用的 Activity、应用逻辑和资源加以重复利用。在合并多个清单时，Gradle 使用同一优先顺序，这样每个构建变体都能在最终清单中定义不同的组件或权限。如需了解有关创建自定义源集的更多信息。