Overview

This is an example of embedding Flutter into Xamarin

The reasons are not so important :)

Embed Flutter

The first major step is prepare flutter project to be embedded

Mostly follow the flutter documentation on embedding flutter app into the native project:
https://flutter.dev/docs/development/add-to-app/ios/project-setup

1. Create Flutter module

flutter create --template module flutter_module

2. Export flutter framework

flutter build ios-framework
flutter build aar

Create Xamarin iOS bindings

Mostly follow Xamarin steps for importing native library (framework)

1. Create project

https://docs.microsoft.com/en-us/xamarin/cross-platform/macios/binding/objective-c-libraries

Create Xamarin iOS Binding project

2. Add BOTH frameworks as native libraries

Check folder flutter_module/build/ios/framework/Debug:

• App.framework
• Flutter.framework

3. Bind basic Flutter methods

So far we just need a few method from the Flutter engine:

• FlutterAppDelegate
• FlutterEngine
• FlutterViewController

Add methods one-by-one as they needed rather than exporting all method (using sharpie tool)

Note: there are no methods to bind from App.framework, it just contains the .dart files

Note: it is important to add both frameworks to the single binding project. Create 2 Xamarin bindings projects for every framework does not work for me.

Use in Xamarin iOS project

	public class AppDelegate : FlutterAppDelegate
	{
		public static FlutterEngine FlutterEngine { get; private set; }

		[Export ("application:didFinishLaunchingWithOptions:")]
		public bool FinishedLaunching (UIApplication application, NSDictionary launchOptions)
		{
			FlutterEngine = new FlutterEngine ("My Flutter Engine");
			FlutterEngine.Run ();

			// Override point for customization after application launch.
			// If not required for your application you can safely delete this method
			return true;
		}
	}

// somewhere in the Xamarin app, when want to show a Flutter controlelr
	void ButtonClicked ()
	{
		var vc = new FlutterViewController (AppDelegate.FlutterEngine, null, null);
		PresentViewController (vc, true, null);
	}

Create Xamarin Android bindings

1. Create project

Create Xamarin Android Binding project

2. Add Flutter AAR

Check folder flutter_module/build/host/outputs/repo/com/example/flutter_module/:

• flutter_release/flutter_release-1.0.aar

3. Copy Flutter Dependencies

Ensure flutter build aar has been invoked, as this command will cache the dependencies in the local gradle cache folder.

1. Go to ~/.gradle/caches/modules-2/files-2.1/io.flutter/
2. Copy jar-files from the next folders to the Xamarin.Bindings.Android/Jars:

• arm64_v8a_release
• armeabi_v7a_release
• x86_64_release
• flutter_embedding_release

The files are:

• arm64_v8a_release-1.0.0-540786dd51f112885a89792d678296b95e6622e5.jar
• armeabi_v7a_release-1.0.0-540786dd51f112885a89792d678296b95e6622e5.jar
• x86_64_release-1.0.0-540786dd51f112885a89792d678296b95e6622e5.jar
• flutter_embedding_release-1.0.0-540786dd51f112885a89792d678296b95e6622e5.jar

NOTE: this kind of build will work only on x86_64 emulators and crash on x86 emulators.
To support x86 emulators you need to reference one more library with x86_release flutter support.

4. Adjust library classes visibility

So far we just need a few adjustments to Metadata.xml:

    <attr path="/api/package[@name='io.flutter.embedding.android']/class[@name='FlutterActivityAndFragmentDelegate']" name="visibility">public</attr>
    <remove-node path="/api/package[@name='io.flutter.embedding.engine.dart']/interface[@name='DartExecutor.IsolateServiceIdListener']"/>

Use in Xamarin Android project

1. Ensure to migrate the project to AndroidX. There was a few issues with Android.Support so I've migrated to AndroidX.

2. Though it works in the app with mixed AndroidX and Android.Support

3. Reference FlutterActivity in AndroidManifest.xml

	<application ...>
		<activity android:name="io.flutter.embedding.android.FlutterActivity" android:theme="@style/AppTheme" android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode" android:hardwareAccelerated="true" android:windowSoftInputMode="adjustResize" />
	</application>

Usage

	public class MainActivity : AppCompatActivity
	{
        static FlutterEngine flutterEngine;

		protected override void OnCreate (Bundle savedInstanceState)
		{
			base.OnCreate (savedInstanceState);

			// ...

			// Create Flutter Engine
            if (flutterEngine == null)
            {
				flutterEngine = new FlutterEngine(this);

				flutterEngine.DartExecutor.ExecuteDartEntrypoint(
                    DartEntrypoint.CreateDefault()
                );

				FlutterEngineCache.Instance.Put("my_engine", flutterEngine);
			}
		}
	}

// somewhere in the Xamarin app, when want to show a Flutter controlelr
	void ButtonClicked ()
	{
		StartActivity (FlutterActivity.WithCachedEngine ("my_engine").Build (this));
	}

Known issues

1. Could not make hot reload to work
2. Release iOS framework size is 340mb, DLLs build from that is 170mb (this related to Apple bitcode)

TODO

1. How to debug flutter code run inside Xamarin app?
2. How to make build smooth (1. build flutter, 2. make Xamarin bindings, 3. use as dependency in the app)?
3. How to embed ViewController/Activity into the navigation flow?
4. How to bind data?
5. How to bind commands?