Failed to post notification on created channel on Android TV

Question

I need an app to create Notifications, which should be there after the app is closed, for another app should read them after some time passes.

I followed a tutorial: https://www.youtube.com/watch?v=UqR7YinI7k4

And later, found out, that I need another implementation, due to higher SDK version.

I came to find this answer, which states, that I need to use a NotificationChannel, to do this:

Failed to post notification on channel "null" Target Api is 26

But, I still got stuck, here is my code:

 protected override void OnCreate(Bundle savedInstanceState)
 {
    base.OnCreate(savedInstanceState);
    Xamarin.Essentials.Platform.Init(this, savedInstanceState);
    // Set our view from the "main" layout resource
    SetContentView(Resource.Layout.activity_main);

    var btnSend = FindViewById<Button>(Resource.Id.btnSend);

    btnSend.Click += (s, e) =>
    {
        Bundle valueSend = new Bundle();
        valueSend.PutString("sendContent", "STF content");

        Intent intent = new Intent(this, typeof(SecondActivity));
        intent.PutExtras(valueSend);
        int NOTIFICATION_ID = 234;
        NotificationManager notificationManager = (NotificationManager)this.GetSystemService(Context.NotificationService);

        string CHANNEL_ID = "my_channel_01";
        string name = "my_channel";
        string Description = "This is my channel";

        NotificationChannel mChannel = new NotificationChannel(CHANNEL_ID, name, NotificationManager.ImportanceHigh);
        mChannel.Description = Description;
        mChannel.EnableLights(true);


        Android.Support.V4.App.TaskStackBuilder stackBuilder = Android.Support.V4.App.TaskStackBuilder.Create(this);
            stackBuilder.AddParentStack(Java.Lang.Class.FromType(typeof(SecondActivity)));
        stackBuilder.AddNextIntent(intent);

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

        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, CHANNEL_ID)
            .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("Notifications") // Set the title
            .SetSmallIcon(Resource.Drawable.navigation_empty_icon)
            .SetContentText("STF Content text"); // the message to display.

        notificationManager.Notify(NOTIFICATION_ID, builder.Build());

    };

Once, I press the button, a toast pops up, which states:

And, unfortunately, I have no idea what to do next, can you help me?

Thank you for your time.

Edit1: Found this in log:

E NotificationService: No Channel found for 
pkg=com.companyname.notifications_app, channelId=my_channel_01, id=234, 
tag=null, opPkg=com.companyname.notifications_app, callingUid=10069, 
userId=0, incomingUserId=0, notificationUid=10069, 
notification=Notification(channel=my_channel_01 pri=0 contentView=null 
vibrate=null sound=null defaults=0x0 flags=0x10 color=0x00000000 vis=PRIVATE)

Edit2: Once I press the button, the following error shows up:

TVNotifService: skipped notification 
StatusBarNotification(pkg=com.companyname.notifications_app 
user=UserHandle{0} id=234 tag=null 
key=0|com.companyname.notifications_app|234|null|10069: 
Notification(channel=my_channel_01 pri=0 contentView=null vibrate=null 
sound=null defaults=0x0 flags=0x10 color=0x00000000 vis=PRIVATE)) userId: 0

Edit3: In the end, the code is working on mobile phones, and for it to be working on Android TVs, the app should be whitelisted on the system.

Answer 1

Ok, you create notification channel, set its values, but I don't see notificationManager.createNotificationChannel(mChannel);
So it's like notificationManager doesn't have NotificationChannel attached.

We do it like this:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel notificationChannel = createChannels(); // here I just create channel and return it
            NotificationManager notificationManager = NotificationHelper.getNotificationManager(context);  // same with NotificationManager
            notificationManager.createNotificationChannel(notificationChannel);  //here I "set" channel for manager
            notificationManager.notify(NotificationHelper.ALARM_TYPE_RTC, repeatedNotification);

        } else {
            NotificationHelper.getNotificationManager(context).notify(NotificationHelper.ALARM_TYPE_RTC, repeatedNotification);
        }

getNotificationManager():

public static NotificationManager getNotificationManager(Context context) {
        return (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    }

createChannels():

@RequiresApi(api = Build.VERSION_CODES.O)
    private NotificationChannel createChannels() {
        NotificationChannel nChannel = new NotificationChannel(
                CHANNEL_ID,
                CHANNEL_NAME,
                NotificationManager.IMPORTANCE_HIGH);
        nChannel.setDescription("MY channel");
        nChannel.enableLights(true);
        nChannel.enableVibration(true);
        nChannel.setLightColor(Color.MAGENTA);
        nChannel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);

        return nChannel;
    }