Mobile App Development for Grocery Delivery

We build mobile apps for grocery delivery — one of the most technically challenging segments. Imagine: a customer opens the app, sees 5,000 products, adds milk to the cart, and a minute later it’s out of stock. How to avoid this? Only real-time inventory synchronization using WebSocket events. A large catalog (thousands of items), real-time stock management, product substitutions, warehouse order picking, last-mile logistics — each of these blocks is a separate system. Our task is to combine them into a single cohesive whole, ensuring stability and speed.

How to Ensure Catalog Performance with Thousands of Items?

The first problem is catalog performance. 5,000+ SKUs, search, filters by categories, promotions, brands. A naive implementation — load everything and filter locally — fails.

The right approach: server-side pagination and filtering. Flutter + Flutter infinite_scroll_pagination: request 20 items, on scroll to the end — next 20. Search is server-side, via PostgreSQL full-text search (tsvector + tsquery) or Elasticsearch for complex queries with typos (fuzzy search via Levenshtein distance).

Caching popular categories in Redis: the main page with promotions and bestsellers updates every 5 minutes, not on every request.

Real-time inventory. An item runs out in the warehouse — it must disappear from the catalog immediately, not by the next sync. Inventory updates via WebSocket or Server-Sent Events (SSE): the client subscribes to a category channel, the server pushes changes.

final wsUrl = Uri.parse('wss://example.com/socket');
final webSocket = await WebSocket.connect(wsUrl);
webSocket.listen((message) {
  // Process inventory event
});

What to Do When an Item Is Out of Stock?

After the order is placed, it goes to the warehouse picker. The picker app is a separate Flutter interface: list of items, barcode scanning for confirmation, marking “out of stock” with substitution suggestion.

Substitutions are a sensitive moment. The picker offers a substitute → the customer receives a push and must confirm or decline. A 5-minute timeout: if no response, an automatic substitution (similar from the same category) is applied or the item is removed from the order with a total recalculation.

This flow requires: WebSocket between the picker app and the customer app, real-time order total recalculation, high-priority push (FCM High Priority, priority: high in payload).

Delivery Slots and Logistics

The customer selects a slot: today 18:00–20:00, tomorrow 10:00–12:00. Available slots are server-side logic: number of active couriers × slot capacity − already booked orders. No hardcoding — dynamic calculation.

Delivery zones: polygons in PostGIS. When entering an address, we check if the point falls within a delivery zone (ST_Contains), and if yes, show available slots for that zone.

Courier tracking — coordinates via WebSocket, marker with animation on flutter_map. Estimated time of arrival via Yandex Routes API taking traffic into account.

Loyalty Program and Personalization

Accumulating points are standard for grocery delivery. But personalization works more effectively: “You usually order milk once a week — it’s probably running out soon.” This is not ML magic, but simple analytics based on order history: purchase frequency × average time between orders = estimated next order date. Push one day before that date.

One-tap cart repopulation: “Repeat last order” — all items in the cart, unavailable ones excluded, the rest with current prices.

Typical Development Mistakes

Implementing the cart only on the client side (SharedPreferences). When logging in from a new device, the cart is lost. The cart should live on the server, synced with the client.

Forgetting about returns. The customer received a spoiled product — there must be a flow in the app: photo + description → return request → decision within 24 hours → refund via YooKassa API.

The cost of developing the client app starts from several million rubles depending on integrations. Support cost after launch is a fixed monthly fee. Up to 40% savings by using Flutter instead of two native teams.

How We Do It: Process and Stack

1. Analytics and prototyping (User Flow, architecture)
2. Design — responsive for iOS and Android
3. Client app development (Flutter)
4. Picker app and courier app development
5. Web admin panel (Laravel)
6. Integrations: 1C, YooKassa, SMS gateways, logistics APIs
7. Testing: unit, widget, integration tests, load testing
8. Deployment to App Store and Google Play, passing moderation
9. Technical documentation, staff training, 2 months of support

Stack

Flutter 3.x + Bloc, Laravel 10 + WebSocket, PostgreSQL + PostGIS + Elasticsearch (for search), Redis, FCM, YooKassa with return support, Yandex MapKit + Yandex Routes API.

The full development cycle of a grocery delivery app from scratch is 28 to 40 weeks depending on the volume of integrations and scalability requirements. We have 7+ years of experience in mobile development and have delivered over 15 projects in the delivery sector. We guarantee stability and support after launch.

We will evaluate your project for free — contact us for a consultation. Order development and we will prepare a commercial proposal.

How to choose cross-platform development: Flutter, React Native, or KMM?

We often work with startups that need two apps—iOS and Android—with a budget for one team. Or corporations that want to release an internal tool in three months on both platforms. Cross-platform development solves a specific economic problem: one codebase instead of two. The question is not 'cross-platform or native'—it's 'which tool for which task.'

Each framework dictates its own stack and imposes limitations. An incorrect choice leads to rewriting the project in six months—we've seen it many times with clients who came to us after a failed first attempt. Therefore, before starting, we conduct an audit of technical requirements and team expertise. With 8+ years of cross-platform experience and 50+ delivered apps, we know the pitfalls firsthand.

The three main players now: Flutter, React Native, and Kotlin Multiplatform Mobile. They solve different problems and are poorly compared head-on. Below, we'll break down how to choose the best option for your project.

How do we choose the technology? 4 steps

1. Requirements analysis — list of native APIs, need for offline work, branded UI or standard.
2. Team assessment — expertise in Dart, JavaScript/Kotlin, availability of an iOS developer.
3. Proof-of-concept — implement a critical scenario on the chosen stack in 2–3 days.
4. Final decision — based on performance benchmarks and maintenance cost.

Case from our practice: a fintech startup needed an MVP on both platforms in 10 weeks. Their team had deep React experience, so we selected React Native. The app passed App Store and Google Play review on the first submission, and they launched on schedule. That choice saved 4 weeks compared to training for Flutter.

Comparison of Flutter and React Native: under the hood

Rendering model

Flutter renders UI independently via the Impeller engine (replaced Skia starting with version 3.10). The platform only provides a canvas—Flutter draws every pixel itself. This means:

• Pixel-perfect on all platforms. The same widget looks identical on iOS and Android—good for branded apps, bad if you need a 'native' look on each platform.
• No dependency on OS version. Material 3 in Flutter works the same on Android 8 and Android 14. System Android components are not involved.
• Platform channels for native code. Access to camera, Bluetooth, NFC—via MethodChannel or EventChannel. flutter_camera, flutter_blue_plus are wrappers over platform channels.

React Native uses native platform components. <View> on iOS is UIView. <Text> is UILabel. This means:

• Native look and feel without extra effort.
• New Architecture (Fabric + TurboModules) with JSI removed the JSON bridge between JS and native code. Synchronous calls work without serialization. This is critical for animations and gestures.
• React Native Reanimated 3 runs worklets on the UI thread—animations at 60/120 fps without blocking the JS thread.

Performance in practice

For most business apps, the performance difference between Flutter and React Native New Architecture is imperceptible. The difference appears in edge cases.

Flutter is slower when interacting with platform APIs via platform channels—each call is asynchronous, with data serialization overhead. google_maps_flutter renders the map via PlatformView—a native UIView/View embedded in the Flutter tree. Before Impeller, this caused performance issues (Hybrid Composition vs Virtual Display). With Impeller, Flutter renders UI 2–3x faster on low-end devices compared to Skia, and PlatformView performance improved by 40%.

React Native is slower in scenarios with heavy JS logic on the main thread. Parsing large JSON, complex computations—these block the JS thread and appear as UI freezes. Solution: Hermes (JS engine optimized for RN) + offloading computations to a native module or react-native-workers. With Hermes, cold start time is reduced by 30–40% compared to JavaScriptCore—that's 2x improvement on older devices.

Ecosystem and maturity

Dart is a barrier to entry for teams with a JS/TS background. It's possible to learn basic Dart in a week, but shifting your mindset to Flutter widgets and widget tree takes longer.

TypeScript in React Native is the de facto standard. A team with React experience becomes productive faster.

When to choose Flutter?

• Need a unified branded UI on all platforms (iOS, Android, Web, Desktop).
• Team is ready for Dart.
• Lots of custom animation and custom UI—Flutter is more predictable.
• The app is not tied to specific native APIs.

When to choose React Native?

• Team has React/TypeScript expertise.
• Need native look and feel.
• Heavy use of native components (Maps, Camera with native capabilities).
• Sharing code with React web via monorepo.

Kotlin Multiplatform Mobile: a different story

KMM solves not a UI problem, but the problem of business logic duplication. The concept: write business logic, networking, caching, validation once in Kotlin. iOS receives a .framework via Kotlin/Native, Android uses the library directly. UI on each platform is native.

// Shared Kotlin code — works on iOS and Android
class UserRepository(
    private val httpClient: HttpClient, // Ktor
    private val database: AppDatabase   // SQLDelight
) {
    suspend fun getUser(id: String): User {
        return database.userQueries.selectById(id).executeAsOneOrNull()
            ?: httpClient.get("$BASE_URL/users/$id").body<User>().also {
                database.userQueries.insert(it)
            }
    }
}

Ktor — HTTP client for KMM (works on iOS via Darwin engine, on Android via OkHttp). SQLDelight generates a typesafe Kotlin API for SQLite, works on both platforms.

Real limitations of KMM

Coroutines on iOS: suspend functions from shared code are called through automatically generated wrappers. SKIE (Swift/Kotlin Interface Enhancer) from Touchlab significantly improves the Swift interface: async/await instead of callbacks, AsyncStream for Flow. Without SKIE, working with coroutines from Swift is inconvenient.

Compose Multiplatform: JetBrains is developing Compose for iOS — UI in Compose works on iOS via Metal. This blurs the line with Flutter: one Compose code for both platforms. Status today: Beta, with early adopters in production (Touchlab, JetBrains own products), but stability is lower than Flutter.

Complexity of iOS integration: XCFramework from KMM module is added to an Xcode project. SPM integration exists and works. But iOS developers must understand the Kotlin API and memory management rules via Kotlin/Native (ARC + Kotlin GC work together, which is not always obvious).

When KMM is justified

The company already has mature iOS and Android teams that duplicate business logic. Switching everything to Flutter or React Native is too radical. KMM allows starting small: extract networking and models into shared code, keep UI native. Gradual migration without rewriting everything.

Typical mistakes in technology selection

Choosing Flutter "because it's a single codebase" for an app heavily reliant on native APIs (custom camera, BLE, background processing). Implementing these via platform channels adds complexity that eats up the development speed advantage.

React Native without understanding the JS thread. Heavy operations on the JS thread cause visible freezes. This is solvable, but requires understanding the architecture—otherwise the app will perform worse than native.

KMM without an iOS developer on the team. Shared Kotlin code requires an iOS engineer who integrates the framework into Xcode, writes SwiftUI on top of KMM APIs, and debugs Kotlin/Native crashes.

What is the development process and timeline?

A cross-platform project goes through the same stages as a native one: requirements audit → stack selection → design → development → testing on real devices of both platforms → publication in App Store and Google Play → support.

Testing on real devices is not optional. An emulator does not reproduce memory issues on budget Android phones and does not show differences in gesture behavior on iOS. We test 40+ scenarios on at least 5 real devices covering both OS versions.

Budget savings compared to two native teams can be up to 40–50%. The cost is calculated individually after analyzing the stack and requirements.

What's included in our work

• Technical audit and stack selection for your project.
• Architecture design (clean architecture, MVVM, BLoC/Redux).
• UI development according to design mockups for both platforms.
• Integration of native modules (camera, geolocation, push notifications).
• CI/CD setup (GitHub Actions, Codemagic).
• Testing on real devices (iOS/Android) — at least 40 scenarios.
• Preparation and publication in App Store and Google Play following guidelines (App Store Review, Google Play Policy).
• Technical support for 3 months after launch.
• Handover of source code, documentation, and access — all turnkey.

We'll evaluate your project in one day—get a consultation on stack selection. Order turnkey development and receive a cross-platform app within the agreed timeline, backed by our experience and guaranteed milestones.