Deep Linking for iOS & Android: Universal, App, Deferred

A user taps a link, goes to the store, installs the app, and lands exactly on the needed screen. Without this, up to 30% of traffic from ad campaigns is lost. Poorly implemented deep linking costs businesses millions in lost conversions annually. Our team, with 10+ years of iOS and Android experience, delivers a turnkey solution in 2–4 weeks.

Three Types of Deep Links: What to Choose?

Custom URL Scheme is the simplest but least reliable. If the app is not installed, the browser shows an error. Multiple apps can register the same scheme — unpredictable which opens. It is only suitable for internal scenarios.

Universal Links (iOS) / App Links (Android) are HTTP/HTTPS links that the system intercepts and opens in the app instead of the browser. If the app is not installed, it falls back to the browser. Reliable, verified, proper fallback. This is the standard for production.

Deferred Deep Links preserve context even if the app is not installed. The user taps → App Store → install → open → correct screen. Implemented via Branch.io, Adjust, or AppsFlyer (Firebase Dynamic Links is no longer supported).

How to Set Up Universal Links on iOS?

A file apple-app-site-association (AASA) is required on the server:

{
  "applinks": {
    "apps": [],
    "details": [
      {
        "appIDs": ["TEAMID.com.company.app"],
        "components": [
          { "/": "/product/*", "comment": "Product pages" },
          { "/": "/profile/*" },
          { "/": "/order/*" },
          { "/": "/promo/*", "?": { "ref": "?" } }
        ]
      }
    ]
  }
}

The AASA must be served with Content-Type: application/json, no redirects, status 200. Apple CDN caches it for up to 48 hours. On iOS 16+, there is a developer mode to speed up updates in debug. In Info.plist, specify domains under com.apple.developer.associated-domains, and handle NSUserActivity in SceneDelegate. More at Apple Documentation.

App Links on Android: Step‑by‑Step Setup

File assetlinks.json on the server:

[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "com.company.app",
    "sha256_cert_fingerprints": ["AA:BB:CC:..."]
  }
}]

SHA256 fingerprint from keystore: keytool -list -v -keystore release.jks. Debug and release fingerprints are different — add both to the production assetlinks.json or use different domains.

In AndroidManifest.xml:

<activity android:name=".MainActivity">
    <intent-filter android:autoVerify="true">
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data
            android:scheme="https"
            android:host="yourdomain.com"
            android:pathPrefix="/product/" />
    </intent-filter>
</activity>

android:autoVerify="true" triggers verification on install. To check: adb shell pm get-app-links com.company.app. If STATE_APPROVED — everything works.

Client‑Side Router: Centralized Handling

No more scattered if (url.contains("product")) throughout the code. A single router with a pending deep links queue in case navigation is not yet initialized.

// Android
class DeepLinkRouter {
    fun handle(intent: Intent, navController: NavController) {
        val uri = intent.data ?: return
        val path = uri.path ?: return

        val route = when {
            path.matches(Regex("/product/(\\d+)")) -> Route.ProductDetail(uri.lastPathSegment ?: return)
            path.matches(Regex("/order/(\\w+)")) -> Route.OrderDetail(uri.lastPathSegment ?: return)
            path == "/profile" -> Route.Profile
            path.startsWith("/promo/") -> {
                val ref = uri.getQueryParameter("ref")
                Route.Promo(uri.lastPathSegment ?: return, ref)
            }
            else -> { openInBrowser(uri); return }
        }
        navController.navigate(route)
    }
}

// iOS
final class DeepLinkRouter {
    func handle(url: URL) {
        guard let components = URLComponents(url: url, resolvingAgainstBaseURL: false) else { return }
        let pathComponents = components.path.split(separator: "/").map(String.init)

        switch pathComponents.first {
        case "product" where pathComponents.count == 2:
            navigationManager.push(.productDetail(id: pathComponents[1]))
        case "order" where pathComponents.count == 2:
            navigationManager.push(.orderDetail(id: pathComponents[1]))
        case "profile":
            navigationManager.push(.profile)
        default:
            UIApplication.shared.open(url)
        }
    }
}

Why Deferred Deep Links Are Critical for Ads?

A regular Universal Link loses context if the app is not installed. Deferred Deep Link remembers parameters (e.g., product id) and passes them after installation. This increases ad conversion by 20–40%. At an average cost per lead of $10, proper deep linking saves up to $3,000 per month on 10,000 installs. For implementation, we use Branch.io or Adjust — they provide SDKs and dashboards for tracking.

What Stages Does Deep Linking Implementation Include?

• Audit of current navigation and URL scheme.
• Design of a router with a pending deep links queue.
• Setup of AASA (iOS) and assetlinks.json (Android).
• Integration of Universal Links / App Links + code handling.
• Connection of Deferred Deep Links via selected SDK.
• Testing on physical devices (iOS and Android).
• Documentation for maintenance and access.
• 30‑day warranty after delivery.

Order a navigation audit — we'll assess the implementation complexity in 2 days.

What Deep Linking Mistakes Are Most Common?

• Redirect to CDN breaks App Links. If the domain redirects to www, AASA is needed on both.
• Wrong Content-Type. AASA must be only application/json.
• Missing onNewIntent handling on Android. Deep link on warm start is ignored.
• Navigation before NavController is ready. Use a queue.

Comparison of Deferred Deep Link Providers

Timeline and Cost

Implementation of Universal Links + App Links + router + deferred deep links takes 2 to 4 weeks. The cost is calculated individually after assessing the scope of work. Contact us for a consultation and preliminary estimate.

Deep link is a fundamental concept without which modern mobile apps cannot be imagined. We'll help you implement it correctly and hassle‑free.

How to Start Integrating API into a Mobile App?

The request goes out, the response doesn't come, timeout — 30 seconds. The user stares at the spinner. No network — mobile card in the subway. Or the network is there, but the server returns 200 with an HTML error page instead of JSON — and the app crashes on JSONDecoder.decode(). We see such cases on every second project. So integrating API into a mobile app is not just calling an endpoint, but designing a reliable network layer: error handling, caching, offline mode, certificate pinning. Order an audit of your current network layer — we will evaluate the project in 1 day. Our team guarantees a thorough analysis and provides a detailed roadmap.

Standard libraries like URLSession and OkHttp provide basic HTTP clients, but for production you need retries with exponential backoff, status code validation, typed deserialization, and network state monitoring. Without this, the app loses data and users. We have been doing mobile development for 5 years and implemented more than 30 projects with API integration on iOS, Android, and Flutter — from startups to enterprise solutions.

How to Choose a Protocol for API Integration?

REST remains the standard for most projects. But when a profile screen needs 5 fields out of 40, GraphQL eliminates over-fetching and reduces traffic by 30–60%. gRPC is justified for thousands of requests per minute (trading, IoT) — binary serialization is 3–5 times faster than JSON. WebSocket is the only choice for real-time without polling (messages, notifications).

Practical example: For a fintech app, we replaced REST (40 fields) with GraphQL — response size dropped from 12 KB to 2.5 KB, screen render time decreased by 70%. Traffic savings were significant. Our certified iOS and Android developers have deep experience with all these protocols — you can rely on proven solutions.

How to Ensure Reliable Connection and Offline-First?

Users lose network in the subway, elevator, tunnel. A mobile app must work without internet — at least in read-only mode. We implement the offline-first pattern:

1. On screen open, first show data from the local cache (Core Data / Room).
2. Simultaneously perform a network request, update UI after response.
3. If network is unavailable — show cached data and a 'no connection' label.
4. When network is restored, automatically synchronize changes.

For HTTP response caching we use URLCache (iOS) and OkHttp Cache (Android) with Cache-Control support. For structured data — SwiftData / Room. NWPathMonitor / ConnectivityManager.NetworkCallback monitor network state and trigger updates.

REST and Client Library Selection

Alamofire (iOS) — de facto standard for Swift projects. On top of URLSession it adds request chaining, response validation, automatic retry, certificate pinning via ServerTrustManager. AF.request() with .validate() returns an error for any status code outside 200–299. Without .validate(), Alamofire considers 404 and 500 as successful responses. With Swift Concurrency — async version via serializingDecodable.

Retrofit (Android) — annotation-based HTTP client on top of OkHttp. An interface with annotations compiles into implementation. @GET, @POST, @Path, @Query, @Body — declarative API description. OkHttp under the hood: connection pooling, transparent gzip, HTTP/2 multiplex. HttpLoggingInterceptor — logging in debug builds. Authenticator — automatic token refresh on 401.

Ktor (KMM/Flutter) — multiplatform HTTP client. On iOS it works via Darwin engine (URLSession), on Android — via OkHttp. Single code for both platforms with KMM architecture.

GraphQL: When REST Falls Short

REST returns a fixed structure. A profile screen needs name, avatar, email — the server sends 40 fields. Over-fetching. GraphQL solves this: the client requests exactly the needed fields. This is critical for mobile where traffic and parsing time are real constraints. Apollo iOS and Apollo Kotlin generate typed classes from schema: schema.graphql + query files → strict types at compile time. Subscriptions via WebSocket — real-time without polling. Limitation: GraphQL is harder to cache at the HTTP level. Apollo uses a normalized in-memory cache InMemoryNormalizedCache — requests with overlapping data update the cache without duplication.

WebSocket: Real-Time Without Extra Traffic

Polling (setInterval every 5 seconds) — battery and traffic waste. WebSocket is a persistent bidirectional connection. iOS: URLSessionWebSocketTask (native, iOS 13+). Android: OkHttp WebSocket. Mandatory reconnect handling: on onFailure — exponential backoff (1s → 2s → 4s → 8s → max 60s). Socket.IO is an overlay with automatic reconnect, but for new projects native WebSocket is preferable (fewer dependencies).

gRPC: For High-Load Services

gRPC with protobuf — binary serialization: smaller size, faster parsing. grpc-swift for iOS, grpc-kotlin for Android. The protobuf schema compiles to typed classes. Streaming (server-side, client-side, bidirectional) is a native feature. Application threshold: high request frequency (trading, IoT) or critical latency. For regular CRUD, REST is simpler to debug and monitor.

Certificate Pinning and Security

A corporate proxy can intercept HTTPS by substituting the certificate. Certificate pinning prevents this: the app accepts only a specific certificate or public key. Alamofire: ServerTrustManager with PinnedCertificatesTrustEvaluator. OkHttp: CertificatePinner with SHA-256 hash. Apple's App Transport Security documentation recommends pinning certificates for sensitive data. Operational complexity: on certificate rotation, older app versions stop working. Solution — pinning to the CA public key or support multiple pins with a grace period.

What Is Included in the Work

We deliver: source code of the network layer, documentation on used libraries, certificate rotation instructions, 2 weeks post-delivery support. Our experience guarantees that the solution will be stable and maintainable.

Timeline and Cost

Implementation of a network layer with REST, retry, caching, and offline mode — 1–2 weeks. Adding GraphQL or WebSocket — another 1–2 weeks. gRPC — 2–3 weeks, including code generation. The cost is calculated individually after analyzing the API and offline behavior requirements. We will evaluate the project in 1 day — contact us for a consultation. Get a reliable API integration with guaranteed quality.