In order for an Android project to be built using Gradle, you need to set up a build script. This will always be called build.gradle, by convention. You will notice, as we go through the basics, that Gradle favors convention over configuration and generally provides default values for settings and properties. This makes it a lot easier to get started with a lot less configuration than that found in systems such as Ant or Maven, which have been the de facto build systems for Android projects for a long time. You do not need to absolutely comply with these conventions though, as it is usually possible to override them if needed.

Gradle build scripts are not written in the traditional XML, but in a domain-specific language (DSL) based on Groovy, a dynamic language for the Java Virtual Machine (JVM). The team behind Gradle believes that using a declarative, DSL-style approach based on a dynamic language has significant advantages over using the more procedural, free-floating style of Ant, or any XML-based approach used by many other build systems.

That does not mean you need to know Groovy to get started with your build scripts. It is easy to read, and if you already know Java, the learning curve is not that steep. If you want to start creating your own tasks and plugins (which we will talk about in later chapters), it is useful to have a deeper understanding of Groovy. However, because it is based on the JVM, it is possible to write code for your custom plugins in Java or any other JVM-based language.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.2.3'
    }
}

apply plugin: 'com.android.application'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1"
}

MyApp
├── build.gradle
├── settings.gradle
└── app
    ├── build.gradle
    ├── build
    ├── libs
    └── src
        └── main
            ├── java
            │   └── com.package.myapp
            └── res
                ├── drawable
                ├── layout
                └── etc.

You can start a new project in Android Studio by clicking on Start a new Android Studio project on the start screen or by navigating to File | New Project… in the IDE itself.

Creating a new project in Android Studio starts with a wizard that helps set everything up. The first screen is for setting up the application name and the company domain. The application name is the name that will be used as the name of the app when it is installed and is used as the toolbar title by default. The company domain is used in combination with the application name to determine the package name, which is the unique identifier for any Android app. If you prefer a different package name, you can still change it by clicking on Edit. You can also change the location of the project on your hard drive.

No files are generated before going through all the steps in the wizard, because the next few steps will define which files need to be created.

Android does not only run on phones and tablets, but also supports a broad range of form factors, such as TV, watches, and glasses. The next screen helps you set up all the form factors you want to target in your project. Depending on what you choose here, dependencies and build plugins are included for development. This is where you decide if you just want to make a phone and tablet app or whether you also want to include an Android TV module, an Android Wear module, or a Google Glass module. You can still add these later, but the wizard makes it easy by adding all the necessary files and configurations. This is also where you choose what version of Android you want to support. If you select an API version below 21, the Android Support Library (including the appcompat library) is automatically added as a dependency.

The following screen suggests adding an activity and provides a lot of options, all of which result in generated code that makes it easier to get started. If you choose to have Android Studio generate an activity for you, the next step is to enter a name for the activity class, the layout file and the menu resource, and also to give the activity a title:

After you go through the entire wizard, Android Studio generates source code for an activity and a fragment, depending on the choices you made during the wizard. Android Studio also generates the basic Gradle files to make the project build. You will find a file called settings.gradle and one called build.gradle on the top level of the project. Inside the app module folder, there is another build.gradle file. We will go into more detail about the content and the purpose of these files in Chapter 2, Basic Build Customization.

You now have several options to trigger a build from inside Android Studio:

In the Gradle tool window, you can try to execute assembleDebug to build, or installDebug to install the app on a device or emulator. We will discuss these tasks in the next part of this chapter, which deals with the Gradle wrapper.