Split out IPostNotifications into an interface

osu.Game/Collections/CollectionManager.cs

@@ -14,6 +14,7 @@ using osu.Framework.Graphics;
 using osu.Framework.Logging;
 using osu.Framework.Platform;
 using osu.Game.Beatmaps;
+using osu.Game.Database;
 using osu.Game.IO;
 using osu.Game.IO.Legacy;
 using osu.Game.Overlays.Notifications;
@@ -27,7 +28,7 @@ namespace osu.Game.Collections
     /// This is currently reading and writing from the osu-stable file format. This is a temporary arrangement until we refactor the
     /// database backing the game. Going forward writing should be done in a similar way to other model stores.
     /// </remarks>
-    public class CollectionManager : Component
+    public class CollectionManager : Component, IPostNotifications
     {
         /// <summary>
         /// Database version in stable-compatible YYYYMMDD format.
@@ -106,9 +107,6 @@ namespace osu.Game.Collections
             backgroundSave();
         });
 
-        /// <summary>
-        /// Set an endpoint for notifications to be posted to.
-        /// </summary>
         public Action<Notification> PostNotification { protected get; set; }
 
         /// <summary>

osu.Game/Database/ArchiveModelManager.cs

@@ -57,9 +57,6 @@ namespace osu.Game.Database
         /// </summary>
         private static readonly ThreadedTaskScheduler import_scheduler_low_priority = new ThreadedTaskScheduler(import_queue_request_concurrency, nameof(ArchiveModelManager<TModel, TFileModel>));
 
-        /// <summary>
-        /// Set an endpoint for notifications to be posted to.
-        /// </summary>
         public Action<Notification> PostNotification { protected get; set; }
 
         /// <summary>

osu.Game/Database/IModelManager.cs

@@ -17,7 +17,7 @@ namespace osu.Game.Database
     /// Represents a model manager that publishes events when <typeparamref name="TModel"/>s are added or removed.
     /// </summary>
     /// <typeparam name="TModel">The model type.</typeparam>
-    public interface IModelManager<TModel>
+    public interface IModelManager<TModel> : IPostNotifications
         where TModel : class
     {
         /// <summary>

osu.Game/Database/IPostNotifications.cs

@@ -0,0 +1,16 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Game.Overlays.Notifications;
+
+namespace osu.Game.Database
+{
+    public interface IPostNotifications
+    {
+        /// <summary>
+        /// And action which will be fired when a notification should be presented to the user.
+        /// </summary>
+        public Action<Notification> PostNotification { set; }
+    }
+}