Expose a way of knowing when carousel's displayed items are updated

osu.Game.Tests/Visual/SongSelectV2/BeatmapCarouselTestScene.cs

@@ -49,6 +49,8 @@ namespace osu.Game.Tests.Visual.SongSelectV2
 
         private int beatmapCount;
 
+        protected int NewItemsPresentedInvocationCount;
+
         protected BeatmapCarouselTestScene()
         {
             store = new TestBeatmapStore
@@ -65,6 +67,8 @@ namespace osu.Game.Tests.Visual.SongSelectV2
         {
             AddStep("create components", () =>
             {
+                NewItemsPresentedInvocationCount = 0;
+
                 Box topBox;
                 Children = new Drawable[]
                 {
@@ -98,6 +102,7 @@ namespace osu.Game.Tests.Visual.SongSelectV2
                             {
                                 Carousel = new BeatmapCarousel
                                 {
+                                    NewItemsPresented = () => NewItemsPresentedInvocationCount++,
                                     BleedTop = 50,
                                     BleedBottom = 50,
                                     Anchor = Anchor.Centre,

osu.Game.Tests/Visual/SongSelectV2/TestSceneBeatmapCarouselFiltering.cs

@@ -34,9 +34,13 @@ namespace osu.Game.Tests.Visual.SongSelectV2
             AddBeatmaps(10, 3);
             WaitForDrawablePanels();
 
+            AddAssert("invocation count correct", () => NewItemsPresentedInvocationCount, () => Is.EqualTo(1));
+
             ApplyToFilter("filter", c => c.SearchText = BeatmapSets[2].Metadata.Title);
             WaitForFiltering();
 
+            AddAssert("invocation count correct", () => NewItemsPresentedInvocationCount, () => Is.EqualTo(2));
+
             CheckDisplayedBeatmapSetsCount(1);
             CheckDisplayedBeatmapsCount(3);
 
@@ -54,6 +58,8 @@ namespace osu.Game.Tests.Visual.SongSelectV2
             ApplyToFilter("remove filter", c => c.SearchText = string.Empty);
             WaitForFiltering();
 
+            AddAssert("invocation count correct", () => NewItemsPresentedInvocationCount, () => Is.EqualTo(3));
+
             CheckDisplayedBeatmapSetsCount(10);
             CheckDisplayedBeatmapsCount(30);
         }

osu.Game/Graphics/Carousel/Carousel.cs

@@ -35,6 +35,11 @@ namespace osu.Game.Graphics.Carousel
     {
         #region Properties and methods for external usage
 
+        /// <summary>
+        /// Called after a filter operation or change in items results in the visible carousel items changing.
+        /// </summary>
+        public Action? NewItemsPresented { private get; init; }
+
         /// <summary>
         /// Height of the area above the carousel that should be treated as visible due to transparency of elements in front of it.
         /// </summary>
@@ -304,6 +309,8 @@ namespace osu.Game.Graphics.Carousel
                 HandleItemSelected(currentSelection.Model);
 
                 refreshAfterSelection();
+
+                NewItemsPresented?.Invoke();
             });
 
             void log(string text) => Logger.Log($"Carousel[op {cts.GetHashCode().ToString()}] {stopwatch.ElapsedMilliseconds} ms: {text}");