Android SDK

The traditional Android development toolkit (Views, Activities, Fragments, XML) using Kotlin/Java. Essential for maintaining the vast ecosystem of pre-Compose applications.

When to Use

Maintaining legacy Android applications (Views/XML).
Building features requiring low-level system interactions not yet wrapped by Compose.
Using libraries that strictly require Fragment/View interoperability.

Quick Start

// build.gradle.kts: viewBinding = true

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.myButton.setOnClickListener {
            Toast.makeText(this, "Clicked!", Toast.LENGTH_SHORT).show()
        }
    }
}

Core Concepts

Lifecycle

Understanding the complex lifecycle of Activities (onCreate, onPause, onDestroy) and Fragments is the hardest but most important part of legacy Android dev to prevent crashes and data loss.

Intents

The messaging object used to request an action from another app component (starting activities, services, broadcasting).

XML Layouts

Defining UI structure in XML files (res/layout/activity_main.xml).

Common Patterns

View Binding

Replaces findViewById. Generates type-safe binding classes for XML layouts.

Null Safety: View references are nullable if they verify across configs.
Type Safety: No casting required.

Repository Pattern (Clean Architecture)

separating data sources (Room, Retrofit) from UI logic (ViewModel).

Coroutines (Structured Concurrency)

Replacing AsyncTask and Threads.

Use lifecycleScope and viewModelScope to automatically cancel tasks when the UI is destroyed.

Best Practices

Do:

Use ViewBinding instead of findViewById or Kotlin Synthetics (Deprecated).
Use Coroutines for background tasks.
Use Dependency Injection (Hilt) to manage complex graphs.
Handle Configuration Changes (Rotation) using ViewModels.

Don't:

Don't block the Main Thread (ANR Risk).
Don't put business logic in Activities/Fragments (God Class anti-pattern).
Don't ignore Fragment lifecycle (don't access views in onDestroyView).

Troubleshooting

android-sdk