87. An Overview of Gradle in Android Studio

Up until this point it has, for the most part, been taken for granted that Android Studio will take the necessary steps to compile and run the application projects that have been created. Android Studio has been achieving this in the background using a system known as Gradle.

It is now time to look at how Gradle is used to compile and package together the various elements of an application project and to begin exploring how to configure this system when more advanced requirements are needed in terms of building projects in Android Studio.

87.1 An Overview of Gradle

Gradle is an automated build toolkit that allows the way in which projects are built to be configured and managed through a set of build configuration files. This includes defining how a project is to be built, what dependencies need to be fulfilled for the project to build successfully and what the end result (or results) of the build process should be.

The strength of Gradle lies in the flexibility that it provides to the developer. The Gradle system is a self-contained, command-line based environment that can be integrated into other environments through the use of plugins. In the case of Android Studio, Gradle integration is provided through the appropriately named Android Studio Plugin.

Although the Android Studio Plug-in allows Gradle tasks to be initiated and managed from within Android Studio, the Gradle command-line wrapper can still be used to build Android Studio based projects, including on systems on which Android Studio is not installed...

87.2 Gradle and Android Studio

Gradle brings a number of powerful features to building Android application projects. Some of the key features are as follows:

87.2.1 Sensible Defaults

Gradle implements a concept referred to as convention over configuration. This simply means that Gradle has a pre-defined set of sensible default configuration settings that will be used unless they are overridden by settings in the build files. This means that builds can be performed with the minimum of configuration required by the developer. Changes to the build files are only needed when the default configuration does not meet your build needs.

87.2.2 Dependencies

Another key area of Gradle functionality is that of dependencies. Consider, for example, a module within an Android Studio project which triggers an intent to load another module in the project. The first module has, in effect, a dependency on the second module since the application will fail to build if the second module cannot...

87.3 The Top-level Gradle Build File

A completed Android Studio project contains everything needed to build an Android application and consists of modules, libraries, manifest files and Gradle build files.

Each project contains one top-level Gradle build file. This file is listed as build.gradle (Project: <project name>) and can be found in the project tool window as highlighted in Figure 87-1:

Figure 87-1

By default, the contents of the top level Gradle build file reads as follows:

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {

    repositories {

        google()

        jcenter()

    }

    dependencies {

        classpath "com.android.tools.build:gradle:4.1.0-rc03"

   ...

87.4 Module Level Gradle Build Files

An Android Studio application project is made up of one or more modules. Take, for example, a hypothetical application project named GradleDemo which contains two modules named Module1 and Module2 respectively. In this scenario, each of the modules will require its own Gradle build file. In terms of the project structure, these would be located as follows:

•Module1/build.gradle

•Module2/build.gradle

By default, the Module1 build.gradle file would resemble that of the following listing:

plugins {

    id 'com.android.application'

}

android {

    compileSdkVersion 29

    buildToolsVersion "30.0.0"

    defaultConfig {

        applicationId "com.ebookfrenzy.demoapp"

        minSdkVersion 26

    ...

87.5 Configuring Signing Settings in the Build File

The “Creating, Testing and Uploading an Android App Bundle” chapter of this book covered the steps involved in setting up keys and generating a signed release APK file using the Android Studio user interface. These settings may also be declared within a signingSettings section of the build.gradle file. For example:

.

.

    defaultConfig {

.

.

    }

    signingConfigs {

        release {

            storeFile file("keystore.release")

            storePassword "your keystore password here"

            keyAlias "your key alias here"

        ...

87.6 Running Gradle Tasks from the Command-line

Each Android Studio project contains a Gradle wrapper tool for the purpose of allowing Gradle tasks to be invoked from the command line. This tool is located in the root directory of each project folder. While this wrapper is executable on Windows systems, it needs to have execute permission enabled on Linux and macOS before it can be used. To enable execute permission, open a terminal window, change directory to the project folder for which the wrapper is needed and execute the following command:

chmod +x gradlew

Once the file has execute permissions, the location of the file will either need to be added to your $PATH environment variable, or the name prefixed by ./ in order to run. For example:

./gradlew tasks

Gradle views project building in terms of a number of different tasks. A full listing of tasks that are available for the current project can be obtained by running the following command from within the project directory...

87.7 Summary

For the most part, Android Studio performs application builds in the background without any intervention from the developer. This build process is handled using the Gradle system, an automated build toolkit designed to allow the ways in which projects are built to be configured and managed through a set of build configuration files. While the default behavior of Gradle is adequate for many basic project build requirements, the need to configure the build process is inevitable with more complex projects. This chapter has provided an overview of the Gradle build system and configuration files within the context of an Android Studio project.