How to write a mobile app on Android: a complete guide

Development for the Android platform opens up enormous opportunities for the programmer, because this operating system is used by the majority of people on the planet. Creating your own product is not just writing code, but a complex process that includes designing architecture, drawing interfaces and strictly following Google guidelines. The path from an idea to a finished APK file may seem thorny, but with the right tools it becomes clear and logical.

In the modern world, the choice of technology stack plays a decisive role. Previously, only Java was the standard, but today the situation has changed dramatically. You have to choose between a classic approach, a modern declarative style, or cross-platform solutions. Each method has its own advantages and disadvantages, which directly affect the development speed and performance of the final product.

In this article we will analyze all the stages of creating an application, from installing the first software to publishing it in the store. We won't delve into complex mathematical algorithms, but rather focus on the practical steps needed to get your first project off the ground. This guide will become the foundation for those who want to enter the world of mobile development consciously.

Choosing a programming language and tools

The first step is to determine the language in which your brainchild will be written. For a long time he was considered the king of Android development Java, and millions of lines of code in existing applications are written in it. However, Google has officially announced the transition to Kotlin as its preferred language. Kotlin is more concise, safer (protects against frequent NullPointerException errors) and is fully compatible with Java libraries.

In parallel with the choice of language, it is worth deciding on the approach to creating the user interface. The traditional method uses XML markup to describe the appearance of screens. This is a reliable method that has been proven over the years, but it requires writing a lot of boilerplate code to link the logic and (View). An alternative is Jetpack Compose a modern toolkit that allows you to build a UI exclusively on Kotlin code, which significantly speeds up the process.

⚠️ Attention: If you are starting to learn development from scratch today, do not waste time on a deep study of outdated approaches to layout. Focus on Jetpack Compose and Kotlin, as support for classic View components will be phased out in future versions of the SDK.

For those who already know web development or want to embrace iOS and Android, there are cross-platform frameworks. Flutter from Google uses the Dart language and allows you to create beautiful interfaces with high performance. React Native from Facebook is based on JavaScript and allows you to use the knowledge of web developers. However, native development in Kotlin always provides the best integration with the device hardware and access to the latest OS features.

Installing and configuring the development environment

The main working environment for creating Android applications is Android Studio. It is a powerful integrated development environment (IDE) based on IntelliJ IDEA. It provides all the necessary tools: a code editor, a visual interface designer, device emulators and performance profilers. You can download it exclusively from the official website of the developer to avoid malicious modifications.

The installation process requires attention to detail, since the environment is quite heavy. When you launch it for the first time, the installation wizard will prompt you to select SDK (Software Development Kit) components. Be sure to make sure that the latest versions of Android SDK Platform and SDK Build-Toolsare installed. You'll also need an emulator for testing if you don't have a real device handy. Creating a virtual device takes time, but it is worth it for debugging on different screen resolutions.

After installation, you need to configure the project. When creating a new project in the menu File → New → New Project you will be prompted to select a template. For beginners, the "Empty Activity" or "Empty Compose Activity" template is ideal. In the project settings window, specify the name, package (usually in the format com.example.appname), language (Kotlin) and minimum SDK version. Choosing the minimum version determines which older phones your application can run on.

The project structure may seem confusing due to the abundance of folders. The main directories with which you will work constantly:

• 📂 app/src/main/java — all application source code, logic and classes are stored here.
• 🎨 app/src/main/res — resources: pictures, strings, colors and XML interface layouts.
• 📜 app/build.gradle — build configuration file, where external libraries are connected and compiler versions are set.
• 📝 AndroidManifest.xml —application passport describing permissions, activities and components.

Application architecture and life cycle

Writing code without understanding the architecture will quickly turn the project into an unreadable mess that is impossible to maintain. In the Android world, the architecture has become the de facto standard MVVM (Model-View-ViewModel). It separates display logic (View), business logic (ViewModel) and data (Model). This separation allows you to test logic independently of the interface and simplifies the work of the team.

The key concept in development is Activity (Activity). This is one screen of the application that the user interacts with. Each activity has a life cycle - a sequence of methods that are called by the system at different points in time. You must clearly understand when an activity is created, when it becomes visible, and when it is destroyed by the system to free up memory.

The main life cycle methods that need to be overridden:

• 💡 onCreate — called when the activity is first created, the interface is initialized here.
• 👁️ onStart — the activity becomes visible to the user, but not yet interactive.
• ▶️ onResume — the application is ready for interaction, the user can press buttons.
• ⏸️ onPause — the activity loses focus (for example, a pop-up window has opened), you need to save temporary data.

⚠️ Attention: Never perform heavy operations (downloading from the network, working with a database) in the main thread (UI Thread). This will result in an error Application Not Responding (ANR) and the interface freezing. Use Coroutines or background threads for such tasks.

To store data and transfer information between components, the Android Jetpack component architecture is used. LiveData or StateFlow allow you to monitor data changes and automatically update the interface when they change. This implements a reactive approach, relieving the developer of manually updating texts and images in the code.

What is Context in Android?

Context is information about the state of the application runtime environment. It provides access to resources, databases and system services. Using the wrong context (for example, storing a reference to an Activity in a static variable) is a common cause of memory leaks.

Creating a user interface

The visual component of the application is what the user comes into direct contact with. If you use the classic approach, the interface is described in XML files. You drag elements around in the designer or write tags by hand. Basic layouts (Layouts) include LinearLayout for arranging elements in a row or column, ConstraintLayout for complex positioning relative to each other, and RecyclerView for displaying long lists.

If your choice fell on Jetpack Composethen the entire interface built using Kotlin functions. This is called a declarative approach: you describe how the UI should look based on the current state of the data. For example, to create a button, just call the function Button(onClick = {... }) { Text("Click me") }. Compose automatically redraws only those parts of the screen that have changed, which improves performance.

An important aspect is responsiveness. Smartphone screens vary greatly in size and pixel density. The use of fixed pixel dimensions is prohibited. It is necessary to use units of measurement dp (density-independent pixels) for sizes and sp (scale-independent pixels) for fonts. This ensures that your application will look neat both on a compact budget device and on a huge tablet.

Themes and resources are used to style elements. It is better to put all colors, lines and sizes into separate files in a folder res/values. This simplifies the localization of the application into other languages and allows you to quickly change the color scheme of the entire project by editing one file instead of hundreds of screens of code.

Working with data and network

Most modern ones Applications do not operate in a vacuum; they require communication with a server or storage of information locally. The standard for working with the network is the library Retrofit. It turns your HTTP API into a Java/Kotlin interface, allowing you to make requests with simple function calls. Retrofit automatically processes JSON responses using converters like Gson or Moshi.

A database is used to store data locally that needs to persist after application restarts. This is an abstraction over SQLite that provides convenient work with objects. You describe entities (tables) using annotations, and the library itself generates the necessary SQL code. Room checks requests at the compilation stage, which prevents many errors. Room. This is an abstraction over SQLite that provides convenient work with objects. You describe entities (tables) using annotations, and the library itself generates the necessary SQL code. Room checks requests at the compilation stage, which prevents many errors.

An example of a simple data model for Room might look like this:

@Entity(tableName ="users")
data class User(
@PrimaryKey val id: Int,
val name: String,
val email: String
)

In addition to databases, DataStore or legacy SharedPreferencesis used to store simple settings (for example, a theme or an authorization token). DataStore is preferable because it works asynchronously and uses Kotlin data streams, which makes the code cleaner and safer.

Tool	Purpose	Difficulty to learn
Retrofit	HTTP requests to server	Low
Room	Local SQLite database	Medium
DataStore	Storing key-value settings	Low
Glide / Coil	Loading and caching of images	Low

Testing and debugging

Writing code is only half the battle. The second, equally important part is to make sure that everything works correctly. Debugging in Android Studio occurs using the tool Logcat. It displays system logs in real time. You can filter messages by tags and severity levels (Error, Warning, Info) to find the cause of the failure or understand the progress of the app.

In addition to manual testing, it is necessary to implement automatic testing. There are two main types of tests: local (Unit tests), which run on the developer’s computer and check the logic, and instrumental (UI tests), which run on an emulator or device and simulate user actions. The framework JUnit is used for unit tests, and Espresso is used to test the interface.

Frequent mistakes made by beginners are associated with incorrect handling of the life cycle or memory leaks. The Profiler in Android Studio allows you to monitor CPU, memory, and network usage. If you see that memory consumption is growing without stopping (Memory Leak), it means that somewhere in the code an object is held by reference for longer than necessary, and the garbage collector cannot remove it.

⚠️ Attention: Always test the application on real devices before releasing it. Emulators do not always correctly reproduce the operation of a sensor, camera, GPS, or the behavior of the system when there is insufficient RAM.

Before the final assembly, it is useful to run code analysis via Lint. This tool scans the project for potential bugs, performance, security, and usability issues. It can tell you where you forgot to check access rights or used an outdated method.

Publish on Google Play

When the application is ready, tested and does not contain critical errors, the moment of publication comes. To publish applications in the Google Play store, you need to register a developer account. This is a paid procedure: you must pay a one-time fee of $25. After registration, you get access to the Google Play Console - the control panel for all your products.

The publication process includes several stages. First you need to create an application in the console, fill out the store page (description, screenshots, promotional video, privacy policy). Pay special attention to the description and keywords, as this affects ASO (App Store Optimization) and the visibility of your product in search. Then you need to download a signed APK or AAB (Android App Bundle) file.

Google moderates each application. Typically the verification takes from several hours to several days. Algorithms and people check the application for compliance with the rules: absence of malicious code, compliance with copyright, correct operation of functions. If your application is rejected, you will receive a detailed email outlining the reasons, after which you can correct the errors and resubmit the build.

It is important to remember the target API level requirements. Google requires that new apps and updates target the latest versions of Android. This ensures that users receive secure and up-to-date applications that use the latest OS security features.

⚠️ Please note: Google Play policies change frequently. Before uploading, be sure to check the App Policies section of the Developer Console for current requirements, especially regarding data collection and advertising.

How long does it take to learn how to write applications?

Basic skills for creating a simple application can be mastered in 2-3 months of intensive training. However, becoming a professional developer (Middle/Senior), capable of creating complex architectural solutions, usually requires 1 to 3 years of constant practice.

Do you need to know mathematics to develop for Android?

For most typical applications (news, stores, social networks), deep knowledge of higher mathematics is not required. The school curriculum and logical thinking are enough. Mathematics is critical only in specific niches: games, graphics, signal processing or machine learning.

Is it possible to develop applications on a phone?

Technically, there are environments like AIDE or Termux that allow you to write code on the device. However, this is extremely inconvenient due to the small screen and the lack of a full keyboard. For serious development, you need a computer with Android Studio.

How to make money on your application?

There are several monetization models: paid sale of the application, in-app purchases (subscriptions, products), display of advertising (AdMob) or Freemium model (basic version is free, extended paid). The choice depends on the type of application and audience.