10 Essential Lessons for Building Your First iOS SDK

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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.