flutter-embedding-native-views

Integrating Platform Views and Web Content

Contents

• Platform Views Architecture
• Web Embedding Architecture
• Workflow: Implementing Android Platform Views
• Workflow: Implementing iOS Platform Views
• Workflow: Embedding Flutter in Web Applications
• Examples

Platform Views Architecture

Platform Views allow embedding native views (Android, iOS, macOS) directly into a Flutter application, enabling the application of transforms, clips, and opacity from Dart.

Android Implementations (API 23+)

Choose the appropriate implementation based on your performance and fidelity requirements:

• Hybrid Composition: Renders Flutter content into a texture and uses SurfaceFlinger to compose both.
  • Pros: Best performance and fidelity for Android views.
  • Cons: Lowers overall application FPS. Certain Flutter widget transformations will not work.
• Texture Layer (Texture Layer Hybrid Composition): Renders Platform Views into a texture. Flutter draws them via the texture and renders its own content directly into a Surface.
  • Pros: Best performance for Flutter rendering. All transformations work correctly.
  • Cons: Quick scrolling (e.g., WebViews) can be janky. SurfaceView is problematic (breaks accessibility). Text magnifiers break unless Flutter is rendered into a TextureView.

iOS & macOS Implementations

• iOS: Uses Hybrid Composition exclusively. The native UIView is appended to the view hierarchy.
  • Limitations: ShaderMask and ColorFiltered widgets are not supported. BackdropFilter has composition limitations.
• macOS: Uses Hybrid Composition (NSView).
  • Limitations: Not fully functional in current releases (e.g., gesture support is unavailable).

Performance Mitigation

Mitigate performance drops during complex Dart animations by rendering a screenshot of the native view as a placeholder texture while the animation runs.

Web Embedding Architecture

Embed Flutter into existing web applications (Vanilla JS, React, Angular, etc.) using either Full Page mode or Embedded (Multi-view) mode.

• Full Page Mode: Flutter takes over the entire browser window. Use an iframe if you need to constrain the Flutter app without modifying the Flutter bootstrap process.
• Embedded Mode (Multi-view): Render Flutter into specific HTML elements (divs). Requires multiViewEnabled: true during engine initialization.
  • Manage views from JavaScript using app.addView() and app.removeView().
  • In Dart, replace runApp with runWidget.
  • Manage the dynamic list of views using WidgetsBinding.instance.platformDispatcher.views and render them using ViewCollection and View widgets.

Workflow: Implementing Android Platform Views

Follow this sequential workflow to implement a Platform View on Android.

Task Progress:

• 1. Determine the composition mode (Hybrid vs. Texture Layer).
• 2. Implement the Dart widget.
• 3. Implement the native Android View and Factory.
• 4. Register the Platform View in the Android host.
• 5. Run validator -> review rendering -> fix manual invalidation issues.

1. Dart Implementation

If using Hybrid Composition, use PlatformViewLink, AndroidViewSurface, and PlatformViewsService.initSurfaceAndroidView. If using Texture Layer, use the AndroidView widget.

2. Native Implementation

Create a class implementing io.flutter.plugin.platform.PlatformView that returns your native android.view.View. Create a factory extending PlatformViewFactory to instantiate your view.

3. Registration

Register the factory in your MainActivity.kt (or plugin) using flutterEngine.platformViewsController.registry.registerViewFactory.

Note: If your native view uses SurfaceView or SurfaceTexture, manually call invalidate on the View or its parent when content changes, as they do not invalidate themselves automatically.

Workflow: Implementing iOS Platform Views

Follow this sequential workflow to implement a Platform View on iOS.

Task Progress:

• 1. Implement the Dart widget using UiKitView.
• 2. Implement the native iOS View (FlutterPlatformView) and Factory (FlutterPlatformViewFactory).
• 3. Register the Platform View in AppDelegate.swift or the plugin registrar.
• 4. Run validator -> review composition limitations -> fix unsupported filters.

Workflow: Embedding Flutter in Web Applications

Follow this sequential workflow to embed Flutter into an existing web DOM.

Task Progress:

• 1. Update flutter_bootstrap.js to enable multi-view.
• 2. Update main.dart to use runWidget and ViewCollection.
• 3. Implement JavaScript logic to add/remove host elements.
• 4. Run validator -> review view constraints -> fix CSS conflicts.

1. JavaScript Configuration

In flutter_bootstrap.js, initialize the engine with multiViewEnabled: true. Use the returned app object to add views: app.addView({ hostElement: document.getElementById('my-div') }).

2. Dart Configuration

Replace runApp() with runWidget(). Create a root widget that listens to WidgetsBindingObserver.didChangeMetrics. Map over WidgetsBinding.instance.platformDispatcher.views to create a View widget for each attached FlutterView, and wrap them all in a ViewCollection.

Examples

Example: Android Texture Layer (Dart)

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

class NativeAndroidView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    const String viewType = 'my_native_view';
    final Map<String, dynamic> creationParams = <String, dynamic>{};

    return AndroidView(
      viewType: viewType,
      layoutDirection: TextDirection.ltr,
      creationParams: creationParams,
      creationParamsCodec: const StandardMessageCodec(),
    );
  }
}

Example: Web Multi-View Initialization (JavaScript)

_flutter.loader.load({
  onEntrypointLoaded: async function(engineInitializer) {
    let engine = await engineInitializer.initializeEngine({
      multiViewEnabled: true,
    });
    let app = await engine.runApp();
    
    // Add a view to a specific DOM element
    let viewId = app.addView({
      hostElement: document.querySelector('#flutter-host-container'),
      initialData: { customData: 'Hello from JS' }
    });
  }
});

Example: Web Multi-View Root Widget (Dart)

import 'dart:ui' show FlutterView;
import 'package:flutter/widgets.dart';

void main() {
  runWidget(MultiViewApp(viewBuilder: (context) => const MyEmbeddedWidget()));
}

class MultiViewApp extends StatefulWidget {
  final WidgetBuilder viewBuilder;
  const MultiViewApp({super.key, required this.viewBuilder});

  @override
  State<MultiViewApp> createState() => _MultiViewAppState();
}

class _MultiViewAppState extends State<MultiViewApp> with WidgetsBindingObserver {
  Map<Object, Widget> _views = {};

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    _updateViews();
  }

  @override
  void didChangeMetrics() => _updateViews();

  void _updateViews() {
    final newViews = <Object, Widget>{};
    for (final FlutterView view in WidgetsBinding.instance.platformDispatcher.views) {
      newViews[view.viewId] = _views[view.viewId] ?? View(
        view: view,
        child: Builder(builder: widget.viewBuilder),
      );
    }
    setState(() => _views = newViews);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return ViewCollection(views: _views.values.toList(growable: false));
  }
}