android studio中3个和构建相关的组件

1. Gradle程序，这是和安卓独立的gradle系统，现在的版本号为6.5；

   在项目中, gradle存储在gradle\wrapper\gradle-wrapper.properties文件中，以下载链接的方式存在。例如：

   在构建中往往出现gradle下载不完全的问题，这时就会报错。打开C:\Users\Administrator\.gradle\wrapper\dists文件夹，就能看到不同版本的gradle文件。

   

   我们可以直接到gradle-wrapper.properties指定的url下载压缩包并放到C:\Users\Administrator\.gradle\wrapper\dists\gradle-5.6.4-bin\bxirm19lnfz6nurbatndyydux类似的位置中。在启动构建时，android studio会自动解压并运行。

2. android sdk build tools.这是安卓sdk中自带的构建工具。我们可以打开这个图标，选择SDK tools栏看到

   即已经安卓了相应的SDK build tools工具。在项目中的文件指定了需要的版本。如这里是29.0.2。打开安卓sdk build-tools目录，如C:\Users\Administrator\AppData\Local\Android\Sdk\build-tools就可以看到工具的所有版本。当出现下载问题时，可以到相应网站下载需要的工具版本，解压后重命名放到sdk build-tools目录中，android studio会自动检测并使用。

3. gradle plugin. 除了以上两种，安卓还提供了一个构建插件。其版本号规定在项目文件中。即对于全局项目，使用的gradle插件是相同的。在打开android studio的时候，往往会提示我们更新gradle插件版本，其实就是指的它。一般情况下，gradle插件并不会导致太大的问题。

gradle plugin 和 Gradle程序的兼容问题

下表列出了每个版本的Android Gradle插件所需的Gradle版本。 为了获得最佳性能，建议使用Gradle和插件的最新版本。

Plugin version	Required Gradle version
1.0.0 - 1.1.3	2.2.1 - 2.3
1.2.0 - 1.3.1	2.2.1 - 2.9
1.5.0	2.2.1 - 2.13
2.0.0 - 2.1.2	2.10 - 2.13
2.1.3 - 2.2.3	2.14.1+
2.3.0+	3.3+
3.0.0+	4.1+
3.1.0+	4.4+
3.2.0 - 3.2.1	4.6+
3.3.0 - 3.3.3	4.10.1+
3.4.0 - 3.4.3	5.1.1+
3.5.0 - 3.5.4	5.4.1+
3.6.0 - 3.6.4	5.6.4+
4.0.0+	6.1.1+
4.1.0+	6.5+

安卓程序的构建

文件结构

安卓项目主要分为三个级别：

1. Project级别：项目包含的所有文件
2. Module级别：例如app等模块，一个项目可以有多个模块。
3. 代码模块，main文件夹下的所有文件。

build.gradle文件结构

主要包含两个文件：

1. 全局构建配置文件build.gradle(Project)

   buildscript {
       repositories {
           jcenter()
           maven {
               url 'https://maven.google.com/'
               name 'Google'
           }
       }
       dependencies {
           classpath 'com.android.tools.build:gradle:3.6.1'
           // NOTE: Do not place your application dependencies here; they belong
           // in the individual module build.gradle files
       }
   }
   
   allprojects {
       repositories {
           jcenter()
           maven {
               url 'https://maven.google.com/'
               name 'Google'
           }
       }
   }
   
   task clean(type: Delete) {
       delete rootProject.buildDir
   }

   位于根项目目录中的全局build.gradle文件定义了适用于项目中所有模块的构建配置。

   默认情况下，buildscript块定义项目中所有模块通用的Gradle存储库和依赖项。

   allprojects块用来配置存储库和所有模块共用的依赖，例如第三方插件和库，默认情况下，这里只包括jcenter和maven存储库。

   dependencies配置了gradle构建项目需要的依赖，关于版本的问题前文已经提到过了。

2. 模块配置文件 build.gradle(Module)

   位于模块的根目录中，主要用于配置其所在的特定模块。我们可以通过配置这些构建设置来提供自定义打包选项，例如其他构建类型和产品类型，并覆盖manifest或全局build.gradle文件中的设置。

   /**
    * 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.
      */
   
     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 "29.0.2"
   
     /**
      * 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 default Proguard rules 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.
      */
   
     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.
      */
   
     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.
    */
   
   dependencies {
       implementation project(":lib")
       implementation 'com.android.support:appcompat-v7:28.0.0'
       implementation fileTree(dir: 'libs', include: ['*.jar'])
   }

参考文献

https://developer.android.com/studio/build

https://developer.android.com/codelabs/android-training-hello-world?index=..%2F..%2Fandroid-training#0