Day 4 有提到為了實現通話功能而多出來的 build.gradle(Module :sinch-android-rtc-3.9.14) 要怎麼處理。

用多出來形容 build.gradle(Module :sinch-android-rtc-3.9.14)，表示其他兩個 build.gradle 是必要的檔案配置。

分別是

1. build.gradle(Project:專案名稱)
2. build.gradle(Module :app)

build.gradle(Project:專案名稱)

位置：位於 Project 根目錄
用途：定義 Project 中模塊使用的通用版本
說明：插件 Android Gradle、Kotlin 會在此聲明；Android Support Library、Google Play Services Library 等支持庫也會在此添加。

plugins {

    /**
     * Use `apply false` in the top-level build.gradle file to add a Gradle
     * plugin as a build dependency but not apply it to the current (root)
     * project. Don't use `apply false` in sub-projects. For more information,
     * see Applying external plugins with same version to subprojects.
     * 
     * 在 build.gradle(Project:專案名稱) 使用 `apply false` 來新增 Gradle 插件
     * 作為構建依賴項。但不把此新增插件套用在當前的 Project 根目錄。
     * 不要把 `apply false` 使用在子 Project。
     * 欲知詳情，請參閱["套用相同版本的外部插件至子 Project"](https://docs.gradle.org/current/userguide/plugins.html#sec:subprojects_plugins_dsl)一文。
     */

     id 'com.android.application' version '8.1.0' apply false
     id 'com.android.library' version '8.1.0' apply false
     id 'org.jetbrains.kotlin.android' version '1.8.22' apply false
}

build.gradle(Module :app)

位置：位於每一個project/module/模塊目錄
用途：為特定模塊配置構建設定
說明：有三個主要部份，插件(Plugins)、Android、依賴項(Dependencies)

/**
 * The first line in the build configuration applies the Android Gradle plugin
 * to this build and makes the android block available to specify
 * Android-specific build options.
 */

plugins {
    id 'com.android.application'
}

/**
 * Locate (and possibly download) a JDK used to build your kotlin
 * source code. This also acts as a default for sourceCompatibility,
 * targetCompatibility and jvmTarget. Note that this does not affect which JDK
 * is used to run the Gradle build itself, and does not need to take into
 * account the JDK version required by Gradle plugins (such as the
 * Android Gradle Plugin)
 */
kotlin {
    jvmToolchain 11
}

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

android {

    /**
     * The app's namespace. Used primarily to access app resources.
     */

    namespace 'com.example.myapp'

    /**
     * compileSdk 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.
     */

    compileSdk 33

    /**
     * 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 {

        // Uniquely identifies the package for publishing.
        applicationId 'com.example.myapp'

        // Defines the minimum API level required to run the app.
        minSdk 21

        // Specifies the API level used to test the app.
        targetSdk 33

        // 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 lets you 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'
        }
    }

    /**
     * To override source and target compatibility (if different from the
     * tool chain JDK version), add the following. All of these
     * default to the same value as kotlin.jvmToolchain. If you're using the
     * same version for these values and kotlin.jvmToolchain, you can
     * remove these blocks.
     */
    //compileOptions {
    //    sourceCompatibility JavaVersion.VERSION_11
    //    targetCompatibility JavaVersion.VERSION_11
    //}
    //kotlinOptions {
    //    jvmTarget = '11'
    //}
}

/**
 * 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 'androidx.appcompat:appcompat:1.6.1'
    implementation fileTree(dir: 'libs', include: ['*.jar'])
}

資料來源：
Google for Developers - Groovy
What is Gradle and why do we use it as Android developers?

build.gradle(Module :app) 的設定要素較多，將在之後的文章來逐一說明。