Push Notifications in Xamarin Forms

Step by step guide:

1) In your shared project, create an Interface called IPushNotificationRegister

public interface IPushNotificationRegister
{
    void ExtractTokenAndRegister();
}

This interface is used for fetching the push token and then send it to the server. this Token is unique per device.

2) In Your shared proejct, you should invoke ExtractTokenAndRegister (using your favourite IOC, I called it right after login).

Android Implementation:

3) Add Receivers for listening to events received by Google GCM service:

a)

[BroadcastReceiver]
[IntentFilter(new[] { Intent.ActionBootCompleted })]
public class GCMBootReceiver : BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
    {
        MyIntentService.RunIntentInService(context, intent);
        SetResult(Result.Ok, null, null);
    }
}

b)

[assembly: Permission(Name = "@PACKAGE_NAME@.permission.C2D_MESSAGE")]
[assembly: UsesPermission(Name = "android.permission.WAKE_LOCK")]
[assembly: UsesPermission(Name = "@PACKAGE_NAME@.permission.C2D_MESSAGE")]
[assembly: UsesPermission(Name = "com.google.android.c2dm.permission.RECEIVE")]
[assembly: UsesPermission(Name = "android.permission.GET_ACCOUNTS")]
[assembly: UsesPermission(Name = "android.permission.INTERNET")]

namespace Consumer.Mobile.Droid.PushNotification
{
    [BroadcastReceiver(Permission = "com.google.android.c2dm.permission.SEND")]
    [IntentFilter(new string[] { "com.google.android.c2dm.intent.RECEIVE" }, Categories = new string[] { "@PACKAGE_NAME@" })]
    [IntentFilter(new string[] { "com.google.android.c2dm.intent.REGISTRATION" }, Categories = new string[] { "@PACKAGE_NAME@" })]
    [IntentFilter(new string[] { "com.google.android.gcm.intent.RETRY" }, Categories = new string[] { "@PACKAGE_NAME@" })]
    [IntentFilter (new[]{ Intent.ActionBootCompleted }, Categories = new[]{ Intent.CategoryDefault })]
    public class GCMBroadcastReceiver : BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)
        {
            MyIntentService.RunIntentInService(context, intent);
            SetResult(Result.Ok, null, null);
        }
    }
}

c) Add Intent service to process the notification

using Android.App;
using Android.Content;
using Android.Graphics;
using Android.Media;
using Android.OS;
using Android.Support.V4.App;
using Consumer.Mobile.Infra;
using Consumer.Mobile.Services.PushNotification;
using Java.Lang;
using XLabs.Ioc;
using TaskStackBuilder = Android.Support.V4.App.TaskStackBuilder;

namespace Consumer.Mobile.Droid.PushNotification
{
    [Service]
    public class MyIntentService : IntentService
    {
        private readonly ILogger _logger;
        private readonly IPushNotificationService _notificationService;
        private readonly IPushNotificationRegister _pushNotificationRegister;

        public MyIntentService()
        {
            _logger = Resolver.Resolve<ILogger>();
            _notificationService = Resolver.Resolve<IPushNotificationService>();
            _pushNotificationRegister = Resolver.Resolve<IPushNotificationRegister>();
        }

        static PowerManager.WakeLock _sWakeLock;
        static readonly object Lock = new object();


        public static void RunIntentInService(Context context, Intent intent)
        {
            lock (Lock)
            {
                if (_sWakeLock == null)
                {
                    // This is called from BroadcastReceiver, there is no init.
                    var pm = PowerManager.FromContext(context);
                    _sWakeLock = pm.NewWakeLock(
                    WakeLockFlags.Partial, "My WakeLock Tag");
                }
            }

            _sWakeLock.Acquire();
            intent.SetClass(context, typeof(MyIntentService));
            context.StartService(intent);
        }

        protected override void OnHandleIntent(Intent intent)
        {
            try
            {
                Context context = this.ApplicationContext;
                string action = intent.Action;

                if (action.Equals("com.google.android.c2dm.intent.REGISTRATION"))
                {
                    HandleRegistration(context, intent);
                }
                else if (action.Equals("com.google.android.c2dm.intent.RECEIVE"))
                {
                    HandleMessage(context, intent);
                }
            }
            finally
            {
                lock (Lock)
                {
                    //Sanity check for null as this is a public method
                    if (_sWakeLock != null)
                        _sWakeLock.Release();
                }
            }
        }

        private void HandleMessage(Context context, Intent intent)
        {

            Intent resultIntent = new Intent(this, typeof(MainActivity));


            TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);

            var c = Class.FromType(typeof(MainActivity));
            stackBuilder.AddParentStack(c);
            stackBuilder.AddNextIntent(resultIntent);

            string alert = intent.GetStringExtra("Alert");
            int number = intent.GetIntExtra("Badge", 0);

            var imageUrl = intent.GetStringExtra("ImageUrl");
            var title = intent.GetStringExtra("Title");

            Bitmap bitmap = GetBitmap(imageUrl);

            PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, (int)PendingIntentFlags.UpdateCurrent);

            NotificationCompat.Builder builder = new NotificationCompat.Builder(this)
                .SetAutoCancel(true) // dismiss the notification from the notification area when the user clicks on it
                .SetContentIntent(resultPendingIntent) // start up this activity when the user clicks the intent.
                .SetContentTitle(title) // Set the title
                .SetNumber(number) // Display the count in the Content Info
                .SetSmallIcon(Resource.Drawable.Icon) // This is the icon to display
                .SetLargeIcon(bitmap)
                .SetSound(RingtoneManager.GetDefaultUri(RingtoneType.Notification))
                .SetContentText(alert); // the message to display.

            // Build the notification:
            Notification notification = builder.Build();

            // Get the notification manager:
            NotificationManager notificationManager =
                GetSystemService(Context.NotificationService) as NotificationManager;

            // Publish the notification:
            const int notificationId = 0;
            notificationManager.Notify(notificationId, notification);
        }

        private void HandleRegistration(Context context, Intent intent)
        {
            var token = intent.GetStringExtra("registration_id");
            _logger.Info(this.Class.SimpleName, "Received Token : " + token);

            if (_pushNotificationRegister.ShouldSendToken(token))
            {
                var uid = Android.Provider.Settings.Secure.GetString(MainActivity.Context.ContentResolver, Android.Provider.Settings.Secure.AndroidId);
                _notificationService.AddPushToken(token, DeviceUtils.GetDeviceType(), uid);
            }
        }


        private Bitmap GetBitmap(string url)
        {

            try
            {
                System.Net.WebRequest request =
                    System.Net.WebRequest.Create(url);
                System.Net.WebResponse response = request.GetResponse();
                System.IO.Stream responseStream =
                    response.GetResponseStream();
                return BitmapFactory.DecodeStream(responseStream);


            }
            catch (System.Net.WebException)
            {
                return null;
            }

        }

    }
}

d) Implement the Interface IPushNotificationRegister:

using Android.App;
using Android.Content;
using Consumer.Mobile.Services;
using Consumer.Mobile.Services.PushNotification;
[assembly: Permission(Name = "@PACKAGE_NAME@.permission.C2D_MESSAGE")]
[assembly: UsesPermission(Name = "@PACKAGE_NAME@.permission.C2D_MESSAGE")]

// Gives the app permission to register and receive messages.
[assembly: UsesPermission(Name = "com.google.android.c2dm.permission.RECEIVE")]

// Needed to keep the processor from sleeping when a message arrives
[assembly: UsesPermission(Name = "android.permission.WAKE_LOCK")]
[assembly: UsesPermission(Name = "android.permission.RECEIVE_BOOT_COMPLETED")]
namespace Consumer.Mobile.Droid.PushNotification
{
    public class PushNotificationRegister : IPushNotificationRegister
    {         
        public override void ExtractTokenAndRegister()
        {
            string senders = AndroidConfig.GCMSenderId;
            Intent intent = new Intent("com.google.android.c2dm.intent.REGISTER");
            intent.SetPackage("com.google.android.gsf");
            intent.PutExtra("app", PendingIntent.GetBroadcast(MainActivity.Context, 0, new Intent(), 0));
            intent.PutExtra("sender", senders);
            MainActivity.Context.StartService(intent);
        }


    }
}

iOS implementation:

4) In your AppDelegate , add the following method:

a)

public override void RegisteredForRemoteNotifications(UIApplication application, NSData deviceToken)
{
    var deviceTokenString = deviceToken.ToString().Replace("<","").Replace(">", "").Replace(" ", "");
    var notificationService = Resolver.Resolve<IPushNotificationService>();
    var pushNotificationRegister = Resolver.Resolve<IPushNotificationRegister>();

    if (pushNotificationRegister.ShouldSendToken(deviceTokenString))
    {
        var uid = UIDevice.CurrentDevice.IdentifierForVendor.AsString();
        notificationService.AddPushToken(deviceTokenString, DeviceUtils.GetDeviceType(), uid);
    }
}

b) Implement IPushNotificationRegister :

using Consumer.Mobile.Services;
using Consumer.Mobile.Services.PushNotification;
using UIKit;

namespace Consumer.Mobile.iOS.PushNotification
{
    public class iOSPushNotificationRegister : IPushNotificationRegister
    {
        public override void ExtractTokenAndRegister()
        {
            const UIRemoteNotificationType notificationTypes = UIRemoteNotificationType.Alert | UIRemoteNotificationType.Badge | UIRemoteNotificationType.Sound;
            UIApplication.SharedApplication.RegisterForRemoteNotificationTypes(notificationTypes);
        }
    }
}

Regarding WP, I didn't implemented it.