Migrating Your Flutter App to the Latest SDK

Migrating Your Mobile App to a New Flutter SDK Version

Our Flutter SDK migration service covers Flutter upgrade, null safety, Flutter breaking changes, Impeller Flutter, Navigator 2.0, go_router migration, Flutter plugins, and Flutter testing. We tackle projects like this every month. Our experience — 5+ years in Flutter and over 30 successful migrations — shows that moving from Flutter 2.x to 3.x is just the tip of the iceberg. We help teams deal with null safety, the new Navigator 2.0, and Material changes. Migrating a production app is not just flutter pub upgrade; it's systematic work that requires planning and expertise.

Why Flutter SDK migration requires a professional approach?

Because a major update breaks not only the code but also dependencies, build configuration, and even widget behavior. With a feature-flag approach we cut migration time by 30% compared to trying to update everything at once. Turnkey — with audit, fixing all breaking changes, and testing on real devices. We provide a 30-day post-migration guarantee and have certified Flutter developers.

What actually breaks during a major upgrade

Null safety: beyond dart migrate

The dart migrate tool does 70-80% of the work — adding ? and ! where the analyzer can infer nullability. The remaining 20-30% is manual work, and that's where bugs hide.

Typical case: a plugin from pub.dev hasn't migrated to null safety and is frozen. Options: fork with a patch, replace with an alternative package, write a wrapper. In a project with 40+ dependencies, this turns into a week of work on dependencies alone.

More dangerous is code that passes migration without errors but changes behavior. A late variable without initialization throws LateInitializationError at runtime where before there was just null. Caught only by tests or in production.

Breaking changes in Material 3

Flutter 3.16+ switched useMaterial3: true by default. If the app uses a custom theme via ThemeData, some components start looking different: button sizes change, AppBar padding changes, TextTheme font hierarchy changes. Apps rejected due to visual changes after an upgrade are not uncommon.

Solution: explicitly set useMaterial3: false during migration, then gradually switch to M3 component by component.

Changes in Navigator and routing

If the app uses go_router, each major release of the package breaks the API in new ways. Migrating from go_router 6.x to 10.x is a full rewrite of the route configuration: GoRoute + ShellRoute instead of nested GoRoute, changes in redirect callback signature, new StatefulShellRoute for persistent navigation.

Rendering changes: Impeller

Flutter 3.10+ enabled Impeller by default on iOS (Android — optional). Impeller eliminates jank from shader compilation but breaks custom CustomPainter implementations using non-standard BlendMode or ImageFilter. After enabling Impeller, you need to run all animations and custom widgets on real devices.

How to properly plan a Flutter SDK migration?

Migration process

Dependency audit — first step. flutter pub outdated shows what's outdated but not breaking changes. We manually read the CHANGELOG of each package in pubspec.yaml for major versions. Dependencies are divided into three categories:

• updated without code changes
• require code changes (API changes)
• no compatible version — needs replacement or fork

Feature-flag approach for large apps. Create a migration branch, update SDK and packages, fix all compilation errors. Then fix step by step, starting with the core layer (models, repositories) and ending with UI.

Testing after migration:

• flutter analyze — static analysis without warnings
• flutter test — entire existing suite must pass
• Golden tests for UI components (if used) need to be regenerated — Impeller renders pixels differently
• Smoke test on physical devices: iOS + Android, budget Android is mandatory

Typical migration errors and their solutions

What's included in the migration work

• Audit of current code and dependencies with report
• Update SDK and all packages, documenting breaking changes
• Fix code: null safety, Material 3, Navigator, Impeller
• Write and update tests (unit, widget, golden)
• Smoke tests on physical iOS and Android devices
• Help with publishing to App Store and Google Play
• 30-day post-migration guarantee for peace of mind

Compared to in-house migration, our systematic approach reduces risk by 50% and accelerates time-to-market by 2x.

Specific problems from practice

In one project (e-commerce, Flutter 2.8 → 3.19), the main difficulty was not in the code but in the flutter_local_notifications plugin. Between versions 9.x and 16.x, the entire Android side changed: new FlutterLocalNotificationsPlugin.initialize() with InitializationSettings, mandatory onDidReceiveNotificationResponse instead of the deprecated callback. Plus Android 13 requires explicit POST_NOTIFICATIONS permission — without it, it silently fails.

Another case: image_picker after update started returning XFile instead of File. Everywhere in the code File(imagePicker.path) was replaced with File(xFile.path) — mechanically, but there were 23 usages across different screens.

Timelines

Pricing is calculated individually after auditing the repository and dependency list. For reference, typical small app migration starts at $1,500, medium apps from $4,000. Get a consultation — we'll evaluate your project and propose a timeline.

Learn more about breaking changes in the official Flutter guide.

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.