从最近的任务中删除应用程序时，Android 通知被取消

Question

I have an app which fires notification on button click. I have created two notification channels, in one i have set SetOngoing to TRUE while in another i have set it to false. Everything works fine, but once i remove my app from recent tasks, notification of secondary channel remains however those of primary channel gets removed. I want my notification to remain there even if my app has been closed completely. Here is my sample code:

//MainActivity.cs

using Android.App;
using Android.OS;
using Android.Content;
using Android.Provider;

namespace NotificationChannels
{
    [Activity(Label = "NotificationChannels", MainLauncher = true, Icon = "@mipmap/icon", Theme = "@style/Theme.AppTheme")]
    public class MainActivity : Activity
    {
        public static string TAG = typeof(MainActivity).Name;

        public const int NOTI_PRIMARY1 = 1100;
        public const int NOTI_PRIMARY2 = 1101;
        public const int NOTI_SECONDARY1 = 1200;
        public const int NOTI_SECONDARY2 = 1201;

        MainUI ui;

        NotificationHelper notificationHelper;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Main);
            notificationHelper = new NotificationHelper(this);
            ui = new MainUI(FindViewById(Resource.Id.activity_main), this);
        }

        public void SendNotification(int id, string title)
        {
            Notification.Builder nb = null;
            switch (id)
            {
                case NOTI_PRIMARY1:
                    nb = notificationHelper.GetNotification1(title, GetString(Resource.String.primary1_body));
                    break;

                case NOTI_PRIMARY2:
                    nb = notificationHelper.GetNotification1(title, GetString(Resource.String.primary2_body));
                    break;

                case NOTI_SECONDARY1:
                    nb = notificationHelper.GetNotification2(title, GetString(Resource.String.secondary1_body));
                    break;

                case NOTI_SECONDARY2:
                    nb = notificationHelper.GetNotification2(title, GetString(Resource.String.secondary2_body));
                    break;
            }
            if (nb != null)
            {
                notificationHelper.Notify(id, nb);
            }
        }

        public void GoToNotificationSettings()
        {
            var i = new Intent(Settings.ActionAppNotificationSettings);
            i.PutExtra(Settings.ExtraAppPackage, PackageName);
            StartActivity(i);
        }

        public void GoToNotificationSettings(string channel)
        {
            var i = new Intent(Settings.ActionChannelNotificationSettings);
            i.PutExtra(Settings.ExtraAppPackage, PackageName);
            i.PutExtra(Settings.ExtraChannelId, channel);
            StartActivity(i);
        }

    }
}





//MainUI.cs

using Android.Widget;
using Android.Views;
using Android.Util;

namespace NotificationChannels
{
    public class MainUI : Java.Lang.Object, View.IOnClickListener
    {
        MainActivity self;

        public MainUI(View root, MainActivity self)
        {
            this.self = self;

            titlePrimary = (TextView)root.FindViewById(Resource.Id.main_primary_title);
            ((Button)root.FindViewById(Resource.Id.main_primary_send1)).SetOnClickListener(this);
            ((Button)root.FindViewById(Resource.Id.main_primary_send2)).SetOnClickListener(this);
            ((ImageButton)root.FindViewById(Resource.Id.main_primary_config)).SetOnClickListener(this);

            titleSecondary = (TextView)root.FindViewById(Resource.Id.main_secondary_title);
            ((Button)root.FindViewById(Resource.Id.main_secondary_send1)).SetOnClickListener(this);
            ((Button)root.FindViewById(Resource.Id.main_secondary_send2)).SetOnClickListener(this);
            ((ImageButton)root.FindViewById(Resource.Id.main_secondary_config)).SetOnClickListener(this);

            ((Button)root.FindViewById(Resource.Id.btnA)).SetOnClickListener(this);
        }

        TextView titlePrimary;
        string TitlePrimaryText
        {
            get
            {
                if (titlePrimary != null)
                {
                    return titlePrimary.Text;
                }
                return string.Empty;
            }
        }

        TextView titleSecondary;
        string TitleSecondaryText
        {
            get
            {
                if (titlePrimary != null)
                {
                    return titleSecondary.Text;
                }
                return "";
            }
        }

        public void OnClick(View view)
        {
            switch (view.Id)
            {
                case Resource.Id.main_primary_send1:
                    self.SendNotification(MainActivity.NOTI_PRIMARY1, TitlePrimaryText);
                    break;
                case Resource.Id.main_primary_send2:
                    self.SendNotification(MainActivity.NOTI_PRIMARY2, TitlePrimaryText);
                    break;
                case Resource.Id.main_primary_config:
                    self.GoToNotificationSettings(NotificationHelper.PRIMARY_CHANNEL);
                    break;

                case Resource.Id.main_secondary_send1:
                    self.SendNotification(MainActivity.NOTI_SECONDARY1, TitleSecondaryText);
                    break;
                case Resource.Id.main_secondary_send2:
                    self.SendNotification(MainActivity.NOTI_SECONDARY2, TitleSecondaryText);
                    break;
                case Resource.Id.main_secondary_config:
                    self.GoToNotificationSettings(NotificationHelper.SECONDARY_CHANNEL);
                    break;
                case Resource.Id.btnA:
                    self.GoToNotificationSettings();
                    break;
                default:
                    Log.Error(MainActivity.TAG, "Unknown click event.");
                    break;
            }
        }
    }
}





//NotificationHelper.cs


using System;
using Android.App;
using Android.Content;
using Android.Graphics;

namespace NotificationChannels
{
    public class NotificationHelper : ContextWrapper
    {
        public const string PRIMARY_CHANNEL = "default";
        public const string SECONDARY_CHANNEL = "second";

        NotificationManager manager;
        NotificationManager Manager
        {
            get
            {
                if (manager == null)
                {
                    manager = (NotificationManager)GetSystemService(NotificationService);
                }
                return manager;
            }
        }

        int SmallIcon => Android.Resource.Drawable.StatNotifyChat;

        public NotificationHelper(Context context) : base(context)
        {
            var chan1 = new NotificationChannel(PRIMARY_CHANNEL,
                    GetString(Resource.String.noti_channel_default), NotificationImportance.Default);
            chan1.LightColor = Color.Green;
            chan1.LockscreenVisibility = NotificationVisibility.Private;
            Manager.CreateNotificationChannel(chan1);

            var chan2 = new NotificationChannel(SECONDARY_CHANNEL,
                    GetString(Resource.String.noti_channel_second), NotificationImportance.High);
            chan2.LightColor = Color.Blue;
            chan2.LockscreenVisibility = NotificationVisibility.Public;
            Manager.CreateNotificationChannel(chan2);
        }

        public Notification.Builder GetNotification1(String title, String body)
        {
            return new Notification.Builder(ApplicationContext, PRIMARY_CHANNEL)
                     .SetContentTitle(title)
                     .SetContentText(body)
                     .SetSmallIcon(SmallIcon)
                     .SetAutoCancel(false)
                     .SetOngoing(true);
        }

        public Notification.Builder GetNotification2(String title, String body)
        {
            return new Notification.Builder(ApplicationContext, SECONDARY_CHANNEL)
                     .SetContentTitle(title)
                     .SetContentText(body)
                     .SetSmallIcon(SmallIcon)
                     .SetAutoCancel(false);
        }

        public void Notify(int id, Notification.Builder notification)
        {
            Manager.Notify(id, notification.Build());
        }

    }
}

Answer 1

That would be the expected behavior. An ongoing notification serves the purpose of letting the user know the application is currently performing some important task.

An ongoing notification cannot be dismissed by the user and needs to be handled by the application. If the application is closed then the ongoing notification would also be dismissed.

So if you need the notification to remain:

1. Start a foreground service - Then similar to a music application the notification will not be dismissed even if the application is swiped away from the recents screen
2. When the application is closing you could send another notification which is not an ongoing notification. You would have to do this in the OnDestroy() method of either an Activity or the Application object