Xamarin Forms - Processing a Notification Click - xamarin

Question

I have a Xamarin Forms application which raises an Android Notification but I'm having trouble creating a simple page that will interact with the user when they click the Notification.
I understand that in Xamarin.Forms there is only 1 activity and so the pending Intent must be to that mainActivity
I have set the LaunchMode to SingleTop and and Intent Filter to match the Intent name used in the pendingIntent
Now when I click the Notification I do get routed to the OnResume of the MainActivity but I don't understand how to:
1) Recognise that I am in this activity because of the notification click - I tried adding an Extra to the pending Intent but it is not there when I inspect this.Intent.Extras
2) Even if I know that I'm in the activity due to the notification click, how do I launch a specific page from the Activity. I'm new to Xamarin but I can't see how to navigate to a Content Page or access the Navigation Stack.
This must be a really common use case but I can't find anything relevant.

Answer 1

Ensure the you have set LaunchMode.SingleTop on your MainActivity:
LaunchMode.SingleTop
[Activity(~~~, LaunchMode = LaunchMode.SingleTop, ~~~]
public class MainActivity
{
~~~~
In your MainActivity (the FormsAppCompatActivity subclass) add a OnNewIntent override:
OnNewIntent:
protected override void OnNewIntent(Intent intent)
{
base.OnNewIntent(intent);
NotificationClickedOn(intent);
}
Now you can check the intent.Action / intent.HasExtra to determine if it is your notification that was send and thus process it. With Xamarin.Forms the easiest would be to use MessagingCenter to send a message that is subscribed to within your .NetStd/PCL Xamarin.Forms code base.
NotificationClickedOn:
void NotificationClickedOn(Intent intent)
{
if (intent.Action == "ASushiNotification" && intent.HasExtra("MessageFromSushiHangover"))
{
/// Do something now that you know the user clicked on the notification...
var notificationMessage = intent.Extras.GetString("MessageFromSushiHangover");
var winnerToast = Toast.MakeText(this, $"{notificationMessage}.\n\n🍣 Please send 2 BitCoins to SushiHangover to process your winning ticket! 🍣", ToastLength.Long);
winnerToast.SetGravity(Android.Views.GravityFlags.Center, 0, 0);
winnerToast.Show();
}
}
Send notification example:
void SendNotifacation()
{
var title = "Winner, Winner, Chicken Dinner";
var message = "You just won a million StackOverflow reputation points";
var intent = new Intent(BaseContext, typeof(MainActivity));
intent.SetAction("ASushiNotification");
intent.PutExtra("MessageFromSushiHangover", message);
var pending = PendingIntent.GetActivity(BaseContext, 0, intent, PendingIntentFlags.CancelCurrent);
using (var notificationManager = NotificationManager.FromContext(BaseContext))
{
Notification notification;
if (Android.OS.Build.VERSION.SdkInt < Android.OS.BuildVersionCodes.O)
{
#pragma warning disable CS0618 // Type or member is obsolete
notification = new Notification.Builder(BaseContext)
.SetContentTitle(title)
.SetContentText(message)
.SetAutoCancel(true)
.SetSmallIcon(Resource.Drawable.icon)
.SetDefaults(NotificationDefaults.All)
.SetContentIntent(pending)
.Build();
#pragma warning restore CS0618 // Type or member is obsolete
}
else
{
var myUrgentChannel = BaseContext.PackageName;
const string channelName = "Messages from SushiHangover";
NotificationChannel channel;
channel = notificationManager.GetNotificationChannel(myUrgentChannel);
if (channel == null)
{
channel = new NotificationChannel(myUrgentChannel, channelName, NotificationImportance.High);
channel.EnableVibration(true);
channel.EnableLights(true);
channel.SetSound(
RingtoneManager.GetDefaultUri(RingtoneType.Notification),
new AudioAttributes.Builder().SetUsage(AudioUsageKind.Notification).Build()
);
channel.LockscreenVisibility = NotificationVisibility.Public;
notificationManager.CreateNotificationChannel(channel);
}
channel?.Dispose();
notification = new Notification.Builder(BaseContext)
.SetChannelId(myUrgentChannel)
.SetContentTitle(title)
.SetContentText(message)
.SetAutoCancel(true)
.SetSmallIcon(Resource.Drawable.icon)
.SetContentIntent(pending)
.Build();
}
notificationManager.Notify(1331, notification);
notification.Dispose();
}
}