inlay

An opinionated Flutter add-to-app framework providing type-safe navigation and cross-platform state sharing for apps that embed Flutter inside a native iOS or Android host.

Why

Integrating Flutter into an existing native app is painful:

• Navigation - There are no official guidelines for seamless navigation between native and Flutter screens. The typical approach is raw MethodChannel calls with arbitrary strings, which is error-prone and not type-safe.
• State - There is no standard way to share data between native code and Flutter, especially when multiple Flutter screens (engines) are involved.

inlay solves both problems with a code-generation-driven, type-safe approach. Engine management (based on FlutterEngineGroup) is handled for you behind the scenes.

Features

• Navigation - Type-safe routing between native and Flutter screens (in both directions), with code-generated route classes for Dart, Swift, and Kotlin. Screens can return a typed result to their caller (declare result: on the route).
• Shared State - A key-value storage layer that stays in sync across all Flutter engines and native code. Changes made anywhere are automatically broadcast to all other consumers.
• Engine Management - The framework creates and destroys Flutter engines automatically. You never interact with FlutterEngineGroup directly (unless you want to).
• Theme & Locale Propagation - InlayAppearance lets the host drive dark mode and an in-app language override across every Flutter engine, live.
• Dialogs & Sheets - Flutter dialogs and bottom sheets rendered in transparent native containers over native screens, with go_router, auto_route, and imperative integrations.
• Native Embeddings - UIKit push/present, SwiftUI (InlayFlutterView, .inlayDialog), Android Activities and Fragments; Jetpack Compose via the optional inlay_compose package.

Quick Start

Route and store classes are generated from annotated Dart schemas by inlay_gen.

1. Define routes (Dart)

// A Flutter screen - navigable from native or from other Flutter screens
@InlayFlutterRoute('/sounds-notifications/:contactId')
class SoundsNotificationsPage {
  const SoundsNotificationsPage({required this.contactId});
  final String contactId;
}

// A Flutter dialog - rendered by Flutter over a native screen
@InlayFlutterDialog('/confirm-delete/:itemId')
class ConfirmDeleteDialog {
  const ConfirmDeleteDialog({required this.itemId});
  final String itemId;
}

// A native screen - navigable from Flutter
@InlayNativeRoute()
class NativeEditProfilePage {
  const NativeEditProfilePage({required this.contactId});
  final String contactId;
}

Run code generation to produce type-safe route classes for Dart, Swift, and Kotlin.

2. Navigate

From Dart (Flutter):

// Open a Flutter screen (creates a new native container with a Flutter engine)
await InlayNavigator.instance.push(
  SoundsNotificationsPage(contactId: 'abc-123'),
);

// Open a native screen from Flutter
await InlayNavigator.instance.push(
  NativeEditProfilePage(contactId: 'abc-123').toNativeRoute(),
);

From Swift (iOS):

InlayNavigator.shared.push(
  from: viewController,
  route: SoundsNotificationsPage(contactId: "abc-123"),
  animated: true
)

From Kotlin (Android):

InlayNavigator.push(context, SoundsNotificationsPage(contactId = "abc-123"))

3. Share state

Define a store (Dart):

@InlayStore(key: 'sounds_notifications')
class SoundsNotificationsStore {
  const SoundsNotificationsStore({
    @InlayStoreKey() required this.contactId,
    this.mute = false,
    this.sound = 'Default',
  });

  final String contactId;
  final bool mute;
  final String sound;
}

Read and write from native - Swift:

let scope = KeyValueStorageImpl.shared.createScope()
let store = SoundsNotificationsStore(storage: scope, contactId: "abc-123")

store.mute = true

scope.startObserving { entries in
    if store.containsChanges(in: entries) {
        // reload from store typed properties
    }
}

Read and write from native - Kotlin:

val scope = KeyValueStorageImpl.createScope()
val store = SoundsNotificationsStore(scope, contactId = "abc-123")

store.mute = true

scope.startObserving { entries ->
    if (store.containsChanges(entries)) {
        // reload from store typed properties
    }
}

On the Flutter side, the generated store can be used directly or combined with the optional InlayCubit helper.

Documentation

• Navigation - Route definitions, dialogs & bottom sheets, cross-boundary navigation, go_router & auto_route integration
• State Management - Stores, native access, optional Cubit integration, cross-engine sync
• Testing - Widget-testing screens that navigate and use stores, via package:inlay/testing.dart fakes
• Example apps - A complete Flutter module plus native iOS and Android host apps exercising every feature

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🛠️ Maintained by LeanCode

This package is built with 💙 by LeanCode. We are top-tier experts focused on Flutter Enterprise solutions.

Why LeanCode?

• Creators of Patrol – the next-gen testing framework for Flutter.

• Production-Ready – We use this package in apps with millions of users.

• Full-Cycle Product Development – We take your product from scratch to long-term maintenance.