Android Development

Android Development Guide

Modern Android development has shifted toward Kotlin as the primary language and Jetpack Compose for UI development. This guide covers essential concepts and best practices for building Android applications.

Getting Started with Kotlin and Jetpack Compose

Kotlin offers significant improvements over Java for Android development, while Jetpack Compose provides a modern declarative UI toolkit.

Key Kotlin Features

Null safety with nullable types and safe calls
Extension functions for adding functionality to existing classes
Coroutines for asynchronous programming
Higher-order functions and lambdas
Data classes for holding data

Jetpack Compose Fundamentals

Jetpack Compose uses a declarative approach to UI development:

@Composable
fun GreetingScreen(name: String) {
    Column(
        modifier = Modifier.padding(16.dp),
        verticalArrangement = Arrangement.Center
    ) {
        Text(
            text = "Hello, $name!",
            style = MaterialTheme.typography.headlineMedium
        )
        Spacer(modifier = Modifier.height(8.dp))
        Button(onClick = { /* Handle click */ }) {
            Text("Click me")
        }
    }
}

Android App Architecture

Google recommends following the architectural principles from Android Architecture Components:

MVVM with Clean Architecture

A common approach combines MVVM with Clean Architecture:

Data Layer: Repositories and data sources
Domain Layer: Use cases and business logic
Presentation Layer: ViewModels and UI components

Example ViewModel Implementation

class TaskViewModel(
    private val taskRepository: TaskRepository
) : ViewModel() {
    
    private val _tasks = MutableStateFlow<List<Task>>(emptyList())
    val tasks: StateFlow<List<Task>> = _tasks.asStateFlow()
    
    init {
        loadTasks()
    }
    
    private fun loadTasks() {
        viewModelScope.launch {
            taskRepository.getTasks().collect { taskList ->
                _tasks.value = taskList
            }
        }
    }
    
    fun addTask(task: Task) {
        viewModelScope.launch {
            taskRepository.addTask(task)
        }
    }
    
    fun deleteTask(taskId: String) {
        viewModelScope.launch {
            taskRepository.deleteTask(taskId)
        }
    }
}

Dependency Injection

Dependency Injection (DI) is a crucial pattern in Android development:

Hilt: Google’s recommended DI solution built on Dagger
Koin: A lightweight DI framework for Kotlin
Dagger: The original DI framework for Android

Jetpack Libraries

Android Jetpack includes a collection of libraries to help developers follow best practices:

ViewModel: For UI-related data handling
LiveData/Flow: For observable data holders
Room: For database access
Navigation: For handling fragment navigation
WorkManager: For background tasks
DataStore: For data storage

Testing Best Practices

A robust testing strategy for Android apps includes:

Unit Tests: For testing individual components (JUnit, Mockito)
Integration Tests: For testing interactions between components
UI Tests: For testing the user interface (Espresso)
End-to-End Tests: For testing complete user flows

Documents