10 Essential Lessons for Building Your First iOS SDK

Building an iOS SDK is not just about writing code — it’s about creating a developer friendly product. Your “customers” are not end-users but other developers. If integration feels clunky, they’ll drop it fast.

Here are 10 essential lessons (with examples) to make your SDK modular, secure, and developer-friendly.

1. Architecture & Code Design

• Modularity – Keep SDK logic self-contained and independent of the host app.
• Public API Surface – Expose only what’s necessary; keep everything else internal.
• Loose Coupling – Use protocols and dependency injection for flexibility.
• Versioning Strategy – Follow semantic versioning (MAJOR.MINOR.PATCH).

❌ Bad Example (Non-Modular SDK)

// Inside SDK
class PaymentSDK {
    func startPayment(using viewController: UIViewController, amount: Double) {
        // Directly depending on the app's CheckoutViewController
        let checkoutVC = CheckoutViewController() // <- App-specific
        checkoutVC.amount = amount
        viewController.present(checkoutVC, animated: true)
    }
}

// Inside SDK
class PaymentSDK {
    func startPayment(using viewController: UIViewController, amount: Double) {
        // Directly depending on the app's CheckoutViewController
        let checkoutVC = CheckoutViewController() // <- App-specific
        checkoutVC.amount = amount
        viewController.present(checkoutVC, animated: true)
    }
}

Problems:

• Relies on the app’s own controller (CheckoutViewController).
• Breaks if the host app renames or changes that flow.
• Not reusable across multiple apps.

✅ Good Example (Modular SDK)

// Inside SDK
public protocol PaymentDelegate: AnyObject {
    func paymentDidSucceed(transactionId: String)
    func paymentDidFail(error: Error)
}

public class PaymentSDK {
    public weak var delegate: PaymentDelegate?

    public init() {}

    public func startPayment(amount: Double) {
        // Self-contained logic
        print("Processing payment of \(amount)")
        
        // Simulate success
        delegate?.paymentDidSucceed(transactionId: "ID after transaction")
    }
}

// Inside SDK
public protocol PaymentDelegate: AnyObject {
    func paymentDidSucceed(transactionId: String)
    func paymentDidFail(error: Error)
}

public class PaymentSDK {
    public weak var delegate: PaymentDelegate?

    public init() {}

    public func startPayment(amount: Double) {
        // Self-contained logic
        print("Processing payment of \(amount)")
        
        // Simulate success
        delegate?.paymentDidSucceed(transactionId: "ID after transaction")
    }
}

And inside the App:

class CheckoutViewController: UIViewController, PaymentDelegate {
    let paymentSDK = PaymentSDK()

    override func viewDidLoad() {
        super.viewDidLoad()
        paymentSDK.delegate = self
    }

    func makePayment() {
        paymentSDK.startPayment(amount: 100.0)
    }

    // MARK: - PaymentDelegate
    func paymentDidSucceed(transactionId: String) {
        print("Payment success: \(transactionId)")
    }

    func paymentDidFail(error: Error) {
        print("Payment failed: \(error.localizedDescription)")
    }
}

class CheckoutViewController: UIViewController, PaymentDelegate {
    let paymentSDK = PaymentSDK()

    override func viewDidLoad() {
        super.viewDidLoad()
        paymentSDK.delegate = self
    }

    func makePayment() {
        paymentSDK.startPayment(amount: 100.0)
    }

    // MARK: - PaymentDelegate
    func paymentDidSucceed(transactionId: String) {
        print("Payment success: \(transactionId)")
    }

    func paymentDidFail(error: Error) {
        print("Payment failed: \(error.localizedDescription)")
    }
}

Key Differences:

• SDK is reusable — no tight coupling.
• Communication happens via delegates/protocols.
• SDK logic is independent of app-specific UI.

2. Integration & Distribution

Offer multiple integration methods:

• Swift Package Manager (SPM)
• CocoaPods
• XCFramework for manual installation

👉 Always provide a clear installation guide with step-by-step instructions and code samples. Keep your SDK lightweight, avoiding large binaries or unnecessary dependencies.

3. Compatibility

• Define minimum iOS deployment target (e.g., iOS 12+).
• Support multiple architectures (arm64, simulator slices).
• Provide Objective-C interoperability if you want wider adoption.

4. Security

• Never store sensitive data in plain text.
• Use Keychain for secrets.
• Validate server communication (SSL Pinning recommended).
• Hide internal logic — only expose safe APIs.
• Consider code obfuscation for sensitive SDKs.

Example: Code Obfuscation

Without obfuscation, binaries can be reverse-engineered:

func verifyPaymentToken(token: String) -> Bool

After obfuscation (using tools like SwiftShield):

func a1B2c3(token: String) -> Bool

This makes reverse-engineering much harder.

5. Performance

• Keep memory usage minimal.
• Run heavy operations off the main thread.
• Profile with Instruments before release.
• Avoid blocking the UI loop.

6. Error Handling

• Use enums for clear error codes:

enum SDKError: Error {
    case networkFailure
    case invalidResponse
}

enum SDKError: Error {
    case networkFailure
    case invalidResponse
}

• Provide developer-friendly error messages.
• Avoid force-unwrapping (!).

7. Documentation

Every SDK should include:

• README with setup and usage guide
• API Reference with /// doc comments
• Inline code comments
• Example project to demonstrate real-world usage

8. Testing

• Unit Tests for all public methods.
• Integration Tests with real app flows.
• CI/CD pipelines to test across devices & iOS versions.
• Ensure backward compatibility on updates.

9. Analytics & Logging

• Provide optional logging for debugging.
• Use log levels (info, debug, error).
• Make analytics opt-in only (respect privacy).

10. Maintenance & Upgrades

Always have a deprecation strategy:

@available(*, deprecated, message: "Use processPayment(_:) instead.")
func oldProcessPayment(_ payment: Payment) {
    processPayment(payment) // Call new implementation
}

@available(*, deprecated, message: "Use processPayment(_:) instead.")
func oldProcessPayment(_ payment: Payment) {
    processPayment(payment) // Call new implementation
}

• Communicate deprecation in release notes & docs.
• Give developers a migration window.
• Remove old APIs only in a major release (semantic versioning).

Final Thoughts

Building an iOS SDK is about more than just code — it’s about building trust with developers.

Keep your SDK modular, secure, and easy to integrate. Write great docs, test it well, and think of it as a product experience. If you do, developers will love adopting it, and your SDK will stand the test of time.