Android is a Linux-based mobile operating system developed and maintained by Google and created primarily to power smart mobile devices such as mobile phones and tablets. The primary interface to interact with the Android operating system is Graphic User Interface (GUI)-based. Users of devices powered by Android manipulate and interact with the operating system environment primarily via a visual touch-based interface by performing gestures such as taps and swipes on the display.

Software can be installed on the Android OS in the form of apps. An app is an application that runs within an environment and performs one or more tasks for the achievement of a goal or a collection of goals. The ability to install applications on mobile devices presented a huge opportunity to both users and application developers. Users take advantage of the features provided...

Before attempting to develop the Tetris game as an Android application, we need to understand the game, its rules, and its constraints.

Tetris is a matching puzzle video game that makes use of tiles. The name Tetris is derived from the words tetra – the Greek numerical prefix for four – and tennis. The tiles in Tetris combine to make up tetrominoes which are geometric shapes composed of four squares connected orthogonally:

As previously mentioned, the user interface is the means by which the user of an application interacts with the app. It cannot be overstated how important the user interface of an application is. Before embarking on the process of actually coding a user interface, it may be helpful to make a graphical representation of the UI to be implemented. This can be done with different tools, such as Photoshop, but for this case, a simple sketch is sufficient:

From the preceding sketch, we can see that we will need two distinct screens in this application: the landing screen and the game screen where the actual gameplay will happen. These two screens will require two separate activities. We'll call these two activities MainActivity and GameActivity.

MainActivity will serve as the entry point of our application. It will contain the user interface and all...

The app manifest is an XML file that is present in every Android application. It is located in the manifests of an application's root folder. The manifest file holds crucial information pertaining to an application on the Android operating system. The information contained in an application's androidManifest.xml must be read by the Android system before an application can be run. Some of the information that must be registered in the app manifest are:

• The Java package name for the application
• The activities present in the application
• Services that are used in the application
• Intent filters that direct implicit intents to an activity
• Descriptions of the broadcast receivers used in the application
• Data pertaining to content providers present in the application
• The classes that implement the various application components
• The permissions that are required...

In this chapter, we took a closer look at the Android application framework. In the process, we learned about several things, such as the seven fundamental Android app components: activities, intents, intent filters, fragments, services, loaders, and content providers.

In addition, we took a close look at the process of creating a layout, the constraint layout, types of layout constraints that exist, string, dimension resources, views, view groups, and working with SharedPreferences. In the next chapter, we will delve further into the world of Tetris and implement the gameplay as well as critical application logic.