SDK Development for Mobile Applications

SDK that doesn't annoy

You spent a month developing a great API, yet integrating your SDK into a mobile app keeps getting postponed. Developers complain about a 50-megabyte binary, lack of documentation, and unpredictable crashes after updates. Each such failure means lost clients and reputation. Over 5 years we've released 20+ SDKs for iOS, Android, and Kotlin Multiplatform — and we know how to make integration fast and painless.

What problems do we solve?

Inconvenient public API

The API surface must be minimal. Everything else should be internal/private. The principle of least exposure is not optional. Every method you expose is a commitment for years. If you're wondering whether to publish it — don't.

Backward compatibility

Backward compatibility is the main contract with clients. We use semantic versioning (Wikipedia): major version only for breaking changes. Adding new methods to an interface is a breaking change for implementers, so instead of extending an interface we add a new one or use default implementations (Swift protocol extensions, Kotlin interface defaults). We mark unstable APIs: @Experimental in Kotlin, @available(*, deprecated) in Swift.

Binary size

Nobody wants to add an SDK and get +5 MB to their app. Strict dependency control: minimize transitive dependencies. If the SDK needs a network layer — we don't pull OkHttp or Alamofire, we write using standard libraries (HttpURLConnection, URLSession). Exception: if the SDK is for a specific ecosystem (e.g., Firebase SDK — Kotlin coroutines are expected there).

How we do it?

Kotlin SDK

We publish via Maven Central or GitHub Packages. build.gradle.kts with MavenPublication, signing via GPG (signing plugin), javadoc.jar mandatory for Maven Central. Artifact coordinates: com.example:sdk-name:1.0.0. For cross-platform SDK — KMP with publication of *-android, *-ios-arm64, *-ios-simulator-arm64 artifacts.

Swift/iOS SDK

Distribution via Swift Package Manager (preferred) or Cocoapods. SPM: Package.swift with explicit .supportedPlatforms, export via XCFramework if native C/Objective-C code. Cocoapods: .podspec with spec.vendored_frameworks or spec.source_files. Binary framework — via binaryTarget in SPM or spec.vendored_frameworks in podspec.

Why thread safety is mandatory for an SDK?

The SDK is called from someone else's code — call order cannot be guaranteed. All public API must be thread-safe or explicitly documented as "call only from main thread". In Kotlin — @WorkerThread/@MainThread annotations + Lint rules. In Swift — @MainActor for UI components of SDK, actor for mutable state.

Lifecycle awareness

Android SDK that holds an Activity context is a memory leak. We use WeakReference<Context> or ApplicationContext. On iOS — similarly, weak references to delegate. If the SDK registers system observers (NotificationCenter, BroadcastReceiver) — explicit deinit/close() with documentation is mandatory.

Configuration and initialization

Builder pattern instead of constructor with 10 parameters. On Android — MySDK.Builder(context).apiKey("...").timeout(30).build(). Initialize in Application.onCreate(), not in Activity. If the SDK requires async init — provide a callback and coroutine-compatible API (suspend fun initialize()).

Error handling

Sealed classes for results (Result<T, SDKError>), not raw exceptions. Document all possible SDKError. On Swift — enum SDKError: Error with LocalizedError. Crashlytics and third-party crash reporters must not be included in the SDK — that's the integrating app's responsibility.

How to minimize SDK size?

Binary size is one of the main quality criteria. We ensure the SDK doesn't bloat the client's app. For this:

• Use minimal third-party dependencies.
• On iOS, avoid including unnecessary architectures in XCFramework, use thin binaries.
• On Android, apply ProGuard/R8 shrink to remove unused code.
• In KMP, choose expect/actual for platform-specific code rather than duplication.

Case: Payment SDK in 4 months

For a partner application (our client is a fintech startup) we developed a payment SDK for iOS and Android. Public API: PaymentSDK.present(from: UIViewController, amount: Decimal, completion: @escaping (PaymentResult) -> Void) on iOS and PaymentSDK.launch(activity, amount, callback) on Android. Inside — native UI (bottom sheet with card fields), encryption via AES-256-GCM, token sent to the client's backend. SDK size: 340 KB (iOS xcframework) and 280 KB (Android aar). Testing — unit tests with mock network layer, integration test project in the same repository. This reduced integration time for the client by 2–3 weeks and decreased bugs by 30%. Compared to analogs, our SDK on Kotlin Multiplatform was 40% faster to develop and 25% smaller in size.

What is included in SDK development?

We provide a full package to make it easy for your clients to integrate the SDK:

• Documentation — API Reference (Dokka for Kotlin, DocC for Swift), README with quickstart, changelog in Keep a Changelog format.
• Test application — a repository with integration examples covering main scenarios.
• Lint rules and custom annotations — for Android via lint-api, warning about errors at compile time.
• Integration support — consultations on compatibility and optimization issues.

val sdk = MySDK.Builder(applicationContext)
    .apiKey("")
    .timeout(30)
    .build()
sdk.initialize()

Timelines and cost

The cost is calculated individually. When developing an SDK, it's important to define upfront: target platforms and OS versions, size requirements, versioning policy, and distribution format. Contact us to evaluate your project — we develop turnkey SDKs from 4 weeks. Get a consultation for your project – we'll help you choose the optimal architecture and estimate the budget.

Mobile App Architecture

The app is built in a single ViewController with 2000 lines. Network calls, business logic, UI updates—all in one place. Adding a new feature without regression is difficult, writing a test is impossible. This isn’t “bad code”—it’s a lack of architecture. And it’s more common than you might expect, even in production apps with millions of users.

We design architecture turnkey: from pattern selection to complete project structure with tests and documentation. In 7–10 days you get clean, modular code ready for scaling.

Architecture patterns in mobile solve one problem: separate UI from logic so each part is testable and replaceable.

MVVM: Basic Pattern

Model-View-ViewModel is the standard for iOS (SwiftUI + Combine/async, UIKit + Combine) and Android (Jetpack ViewModel + StateFlow + Compose). The ViewModel holds UI state and business logic. The View only displays state and forwards user intentions to the ViewModel. The Model represents data and its source.

Key rule: ViewModel knows nothing about UIKit or Android View classes. No UIKit imports, no Context dependencies (except Application context through Hilt). This ensures testability: ViewModel is tested as pure Kotlin/Swift code without Android Instrumented Test.

MVVM covers 70% of needs. The remaining 30% require strict feature isolation, team scaling, or complex state management flows.

Clean Architecture: When MVVM Isn’t Enough

Adds layers on top of MVVM:

• Domain layer — business logic, platform-independent. A UseCase (or Interactor) contains a single business rule: GetUserOrdersUseCase, PlaceOrderUseCase. Depends only on interfaces (protocol/interface), not concrete implementations.
• Data layer — repository implementations. OrderRepositoryImpl implements OrderRepository from domain. Knows about Retrofit, Room, UserDefaults. The ViewModel doesn’t know where data comes from—network or cache.
• Presentation layer — ViewModel + View. Knows about Domain, not Data.

Dependency rule: dependencies point inward only. Domain depends on nothing. Data and Presentation depend on Domain.

Presentation → Domain ← Data

This allows swapping implementations: tests use an in-memory repository instead of network, the interface remains the same.

Practical caveat: Clean Architecture adds files and layers. For small apps, this is overhead. It’s justified starting from ~15 features and teams of 3+ developers.

BLoC for Flutter: Predictable State Flow

BLoC (Business Logic Component) is the standard pattern in the Flutter community. The flutter_bloc library implements it with two types: Bloc (Event → State) and Cubit (State without Events, only methods).

Bloc processes Event and emits a new State via on<EventType> handlers. State is immutable—a new object for each change. BlocBuilder re-renders only the part of the tree where state changed.

// Event
abstract class CartEvent {}
class AddItemToCart extends CartEvent {
  final String productId;
  AddItemToCart(this.productId);
}

// State
abstract class CartState {}
class CartLoaded extends CartState {
  final List<CartItem> items;
  CartLoaded(this.items);
}

// Bloc
class CartBloc extends Bloc<CartEvent, CartState> {
  CartBloc(this._cartRepository) : super(CartLoaded([])) {
    on<AddItemToCart>(_onAddItem);
  }

  Future<void> _onAddItem(AddItemToCart event, Emitter<CartState> emit) async {
    final current = state as CartLoaded;
    final updated = await _cartRepository.addItem(event.productId);
    emit(CartLoaded(updated));
  }
}

The advantage of BLoC is testability. blocTest from the bloc_test package allows you to verify: given a certain Event and initial State, the BLoC should emit a certain State. No UI, no mocks for the Flutter framework.

VIPER: For Large iOS Projects

VIPER (View, Interactor, Presenter, Entity, Router) is the strictest separation of responsibilities for iOS. Each component has a protocol and concrete implementation.

• View — UI only, delegates everything to Presenter
• Interactor — business logic, network and data operations
• Presenter — mediator between View and Interactor, formats data for View
• Entity — data models (pure structures)
• Router — navigation between modules

Each module (screen or feature) is a separate VIPER module. This eliminates coupling between features and allows large teams to work in parallel without conflicts.

The cost: many files, many protocols. Boilerplate is generated via Sourcery or custom Xcode templates. VIPER is justified for apps with 10+ developers and 50+ screens.

TCA (The Composable Architecture)

TCA by Point-Free is a more modern alternative to VIPER for iOS/macOS. Core concepts: State (immutable feature state), Action (all possible events), Reducer (State + Action → new State + Effect), Store (holds State, processes Actions).

Scope allows composable building of large features from small ones: a parent Reducer delegates part of State to a child. Each feature is tested in isolation via TestStore with precise control over Effects.

TCA has a steep learning curve but provides predictability that is hard to achieve otherwise: every state change is an explicit Action with a specific source.

Which Pattern to Choose for Your Project?

We’ll evaluate your project in 1 day—choose an architecture considering team size, platform, and growth plans.

There is no universal answer. Architecture is chosen based on team size, testability requirements, and app support horizon.

What Components Are Included in Our Architecture Work?

• Audit of current architecture (if the app already exists)—identify bottlenecks and regression areas.
• Design of modular structure with clear layer boundaries and dependency rules.
• Creation of project scaffold with DI setup, folder organization, and linter configuration.
• Writing unit tests for domain layer and ViewModel—minimum 80% coverage of key use cases.
• Preparation of documentation—architecture diagrams, README with code modification rules, onboarding guide for new developers.
• Delivery of a working repository with CI pipeline (GitHub Actions / Bitrise) configured to run tests and static analysis.

All this is included in the design cost. Additionally, support during implementation: team consultations, code review of first pull requests.

How Does Lack of Architecture Affect Development Speed?

Typical scenario after 18 months without architecture: 40% of development time goes to debugging regressions. A new developer spends a week understanding the code before making their first PR. Tests aren’t written “because it’s hard to mock.” Adding a new feature requires understanding half the codebase.

Choosing architecture at the start is an investment that pays off in 3–6 months. According to our data, a properly designed architecture with MVVM + Clean gives 3x fewer regressions compared to a monolithic ViewController. And the cost of implementation is recouped in 2–3 sprints.

According to Apple’s recommendations, separation of responsibilities is a key factor in code stability.

Why Trust Our Team with Architecture?

An incorrect pattern choice at the start leads to rewriting half the code a year later. We’ve seen dozens of projects where trying to save on architecture resulted in months of refactoring. With over 10 years of commercial development experience and work on apps from 1 to 50 developers, we help avoid common mistakes:

• Overengineering for a simple MVP (we assign MVVM, not VIPER).
• Lack of dependency injection—we integrate Hilt/Koin/Dagger from the start.
• Ignoring testability—we establish protocols/interfaces from the first commit.

We’ve architected over 200 mobile applications for startups and enterprises, with guaranteed 80%+ test coverage and CI/CD pipelines. Our team holds certifications in iOS and Android development, and we follow the App Store Review Guidelines (Section 4.2/5.1) to ensure smooth store approvals.

Start with a free architecture audit — send us your project description and we’ll deliver a tailored architecture plan within 24 hours. Reach out via Telegram or email to get started.