Minimal FCM Push Messaging for .NET MAUI (RC3)

README

* Setup Firebase project like normal and add google-services.json (make sure Build action is set to GoogleServicesJson)
* Nugets required for MAUI project file: (later versions don't work)

    <ItemGroup Condition="'$(TargetFramework)' == 'net6.0-android'">
        <PackageReference Include="Xamarin.Firebase.Iid" Version="121.1.0" />
        <PackageReference Include="Xamarin.Firebase.Messaging" Version="122.0.0" />
        <PackageReference Include="Xamarin.Google.Dagger" Version="2.39.1" />
        <PackageReference Include="Xamarin.GooglePlayServices.Base" Version="117.6.0.5" />
    </ItemGroup>
    
* Also add the receiver configuration to the app manifest's application node:

		<receiver
			android:name="com.google.firebase.iid.FirebaseInstanceIdInternalReceiver"
			android:exported="false" />
		<receiver
			android:name="com.google.firebase.iid.FirebaseInstanceIdReceiver"
			android:exported="true"
			android:permission="com.google.android.c2dm.permission.SEND">
			<intent-filter>
				<action android:name="com.google.android.c2dm.intent.RECEIVE" />
				<action android:name="com.google.android.c2dm.intent.REGISTRATION" />
				<category android:name="${applicationId}" />
			</intent-filter>
		</receiver>

FCMService.cs

using Android.App;
using Android.Content;
using AndroidX.Core.App;
using Firebase.Messaging;

namespace FCMApp.Android;

[Service(Exported = false)]
[IntentFilter(new[] { "com.google.firebase.MESSAGING_EVENT" })]
public class FCMService : FirebaseMessagingService
{
    public override void OnMessageReceived(RemoteMessage message)
    {
        RemoteMessage.Notification notification = message.GetNotification();

        IDictionary<string, string> data = message.Data;
        string body = "";
        string title = "";

        if (data != null && data.ContainsKey("body") && data.ContainsKey("title"))
        {
            body = data["body"];
            title = data["title"];
        }
        else if (notification != null)
        {
            body = message.GetNotification().Body;
            title = message.GetNotification().Title;
        }
        if (!string.IsNullOrEmpty(body) && !string.IsNullOrEmpty(title))
        {
            // TODO: Manage this message (we get here only when app is in foreground)
        }
    }

}

IMessagingService.cs

namespace FCMApp;

public interface IMessagingService
{
    string GetToken();
    bool IsMessagingAvailable();
    void SetNewTokenCallback(Action<string> token_callback);
}
    

MainActivity.cs

using Android.App;
using Android.Content.PM;
using Android.OS;
using Android.Util;

namespace FCMApp;

[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
public class MainActivity : MauiAppCompatActivity
{
    static readonly string TAG = "MainActivity";
    public static readonly string CHANNEL_ID = "main_channel";
    public static readonly int NOTIFICATION_ID = 100;

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

        // handle incoming intent extras (when clicking on a push notification)
        if (Intent.Extras != null)
        {
            foreach (var key in Intent.Extras.KeySet())
            {
                var value = Intent.Extras.GetString(key);
                Log.Debug(TAG, "Key: {0} Value: {1}", key, value);
            }
        }
        CreateNotificationChannel();
    }
    
    void CreateNotificationChannel()
    {
        // notification channel mandatory only from API 26
        if (Build.VERSION.SdkInt < BuildVersionCodes.O)
            return;

        NotificationManager mgr = (NotificationManager)GetSystemService(NotificationService);
        mgr.CreateNotificationChannel(
            new NotificationChannel(CHANNEL_ID, "FCM Notifications", NotificationImportance.Default)
            {
                Description = "Firebase Cloud Messages appear in this channel"
            });
    }
}

MessagingService.Android.cs

using Android.Gms.Common;
using Android.Gms.Tasks;
using Firebase.Iid;

namespace FCMApp;

public partial class MessagingService
{
    public partial bool IsMessagingAvailable() => GoogleApiAvailability.Instance.IsGooglePlayServicesAvailable(Android.App.Application.Context) == ConnectionResult.Success;
    public partial string GetToken() => FirebaseInstanceId.Instance.Token;
    public partial void SetNewTokenCallback(Action<string> token_callback)
    {
        if (token_callback == null)
            throw new InvalidOperationException("Callback cannot be null");
        
        if (GetToken() != null)
            token_callback(GetToken());
        else
            FirebaseInstanceId.Instance.GetInstanceId().AddOnSuccessListener(new OnTokenListener((token) => token_callback(token)));
    }
}

public class OnTokenListener : Java.Lang.Object, IOnSuccessListener
{
    Action<string> _callback;
    public OnTokenListener(Action<string> success_callback) => _callback = success_callback;
    public void OnSuccess(Java.Lang.Object result) => _callback?.Invoke(FirebaseInstanceId.Instance.Token);
}

MessagingService.cs

namespace FCMApp;

public partial class MessagingService : IMessagingService
{
    public partial string GetToken();
    public partial bool IsMessagingAvailable();
    public partial void SetNewTokenCallback(Action<string> token_callback);
}

Thanks for sharing, however methods are not hitting, could you please share working example code?