Add basic pooling setup

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -16,6 +16,7 @@ using osu.Framework.Bindables;
 using osu.Framework.Caching;
 using osu.Framework.Threading;
 using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Framework.Graphics.Pooling;
 using osu.Framework.Input.Bindings;
 using osu.Framework.Input.Events;
 using osu.Game.Beatmaps;
@@ -136,6 +137,8 @@ namespace osu.Game.Screens.Select
         private IBindable<WeakReference<BeatmapInfo>> itemHidden;
         private IBindable<WeakReference<BeatmapInfo>> itemRestored;
 
+        private readonly DrawablePool<DrawableCarouselBeatmapSet> setPool = new DrawablePool<DrawableCarouselBeatmapSet>(100);
+
         public BeatmapCarousel()
         {
             root = new CarouselRoot(this);
@@ -146,11 +149,15 @@ namespace osu.Game.Screens.Select
                 {
                     Masking = false,
                     RelativeSizeAxes = Axes.Both,
-                    Child = scrollableContent = new Container<DrawableCarouselItem>
+                    Children = new Drawable[]
+                    {
+                        setPool,
+                        scrollableContent = new Container<DrawableCarouselItem>
                         {
                             RelativeSizeAxes = Axes.X,
                         }
                     }
+                }
             };
         }
 
@@ -580,11 +587,13 @@ namespace osu.Game.Screens.Select
                 // Add those items within the previously found index range that should be displayed.
                 for (int i = firstIndex; i < lastIndex; ++i)
                 {
-                    var panel = scrollableContent.FirstOrDefault(c => c.Item == visibleItems[i]);
+                    var item = visibleItems[i];
+
+                    var panel = scrollableContent.FirstOrDefault(c => c.Item == item);
 
                     if (panel == null)
                     {
-                        panel = visibleItems[i].CreateDrawableRepresentation();
+                        panel = setPool.Get(p => p.Item = item);
                         scrollableContent.Add(panel);
                     }
 

osu.Game/Screens/Select/Carousel/CarouselBeatmapSet.cs

@@ -43,8 +43,6 @@ namespace osu.Game.Screens.Select.Carousel
                       .ForEach(AddChild);
         }
 
-        public override DrawableCarouselItem CreateDrawableRepresentation() => new DrawableCarouselBeatmapSet(this);
-
         protected override CarouselItem GetNextToSelect()
         {
             if (LastSelected == null)

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmap.cs

@@ -60,10 +60,12 @@ namespace osu.Game.Screens.Select.Carousel
         private CancellationTokenSource starDifficultyCancellationSource;
 
         public DrawableCarouselBeatmap(CarouselBeatmap panel)
-            : base(panel)
         {
             beatmap = panel.Beatmap;
             Height = HEIGHT;
+
+            // todo: temporary
+            Item = panel;
         }
 
         [BackgroundDependencyLoader(true)]
@@ -79,7 +81,7 @@ namespace osu.Game.Screens.Select.Carousel
             if (manager != null)
                 hideRequested = manager.Hide;
 
-            Children = new Drawable[]
+            Content.Children = new Drawable[]
             {
                 background = new Box
                 {

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmapSet.cs

@@ -45,26 +45,40 @@ namespace osu.Game.Screens.Select.Carousel
 
         public override IEnumerable<DrawableCarouselItem> ChildItems => beatmapContainer?.Children ?? base.ChildItems;
 
-        private readonly BeatmapSetInfo beatmapSet;
+        private BeatmapSetInfo beatmapSet => (Item as CarouselBeatmapSet)?.BeatmapSet;
 
         private Container<DrawableCarouselBeatmap> beatmapContainer;
         private Bindable<CarouselItemState> beatmapSetState;
 
-        public DrawableCarouselBeatmapSet(CarouselBeatmapSet set)
+        [Resolved]
-            : base(set)
+        private BeatmapManager manager { get; set; }
-        {
-            beatmapSet = set.BeatmapSet;
-        }
 
         [BackgroundDependencyLoader(true)]
-        private void load(BeatmapManager manager, BeatmapSetOverlay beatmapOverlay)
+        private void load(BeatmapSetOverlay beatmapOverlay)
         {
             restoreHiddenRequested = s => s.Beatmaps.ForEach(manager.Restore);
 
             if (beatmapOverlay != null)
                 viewDetails = beatmapOverlay.FetchAndShowBeatmapSet;
 
-            Children = new Drawable[]
+            // TODO: temporary. we probably want to *not* inherit DrawableCarouselItem for this class, but only the above header portion.
+            AddRangeInternal(new Drawable[]
+            {
+                beatmapContainer = new Container<DrawableCarouselBeatmap>
+                {
+                    X = 50,
+                    Y = MAX_HEIGHT,
+                    RelativeSizeAxes = Axes.X,
+                    AutoSizeAxes = Axes.Y,
+                },
+            });
+        }
+
+        protected override void UpdateItem()
+        {
+            base.UpdateItem();
+
+            Content.Children = new Drawable[]
             {
                 new DelayedLoadUnloadWrapper(() =>
                     {
@@ -125,17 +139,7 @@ namespace osu.Game.Screens.Select.Carousel
                 }
             };
 
-            // TODO: temporary. we probably want to *not* inherit DrawableCarouselItem for this class, but only the above header portion.
+            beatmapContainer.Clear();
-            AddRangeInternal(new Drawable[]
-            {
-                beatmapContainer = new Container<DrawableCarouselBeatmap>
-                {
-                    X = 50,
-                    Y = MAX_HEIGHT,
-                    RelativeSizeAxes = Axes.X,
-                    AutoSizeAxes = Axes.Y,
-                },
-            });
 
             beatmapSetState = Item.State.GetBoundCopy();
             beatmapSetState.BindValueChanged(setSelected, true);
@@ -153,11 +157,16 @@ namespace osu.Game.Screens.Select.Carousel
 
                     float yPos = 0;
 
-                    foreach (var item in ((CarouselBeatmapSet)Item).Beatmaps.Select(b => b.CreateDrawableRepresentation()).OfType<DrawableCarouselBeatmap>())
+                    var carouselBeatmapSet = (CarouselBeatmapSet)Item;
+
+                    foreach (var item in carouselBeatmapSet.Children)
                     {
-                        item.Y = yPos;
+                        var beatmapPanel = item.CreateDrawableRepresentation();
-                        beatmapContainer.Add(item);
+
-                        yPos += item.Item.TotalHeight;
+                        beatmapPanel.Y = yPos;
+                        yPos += item.TotalHeight;
+
+                        beatmapContainer.Add((DrawableCarouselBeatmap)beatmapPanel);
                     }
 
                     break;

osu.Game/Screens/Select/Carousel/DrawableCarouselItem.cs

@@ -2,14 +2,17 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
+using osu.Framework.Bindables;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Effects;
+using osu.Framework.Graphics.Pooling;
 using osu.Framework.Graphics.Shapes;
 using osu.Framework.Input.Events;
 using osu.Framework.Utils;
@@ -19,15 +22,32 @@ using osuTK.Graphics;
 
 namespace osu.Game.Screens.Select.Carousel
 {
-    public abstract class DrawableCarouselItem : Container
+    public abstract class DrawableCarouselItem : PoolableDrawable
     {
         public const float MAX_HEIGHT = 80;
 
-        public override bool RemoveWhenNotAlive => false;
+        public override bool IsPresent => base.IsPresent || Item?.Visible == true;
 
-        public override bool IsPresent => base.IsPresent || Item.Visible;
+        public CarouselItem Item
+        {
+            get => item;
+            set
+            {
+                if (item == value)
+                    return;
 
-        public readonly CarouselItem Item;
+                if (item != null)
+                {
+                    Item.Filtered.ValueChanged -= onStateChange;
+                    Item.State.ValueChanged -= onStateChange;
+                }
+
+                item = value;
+
+                if (IsLoaded)
+                    UpdateItem();
+            }
+        }
 
         public virtual IEnumerable<DrawableCarouselItem> ChildItems => Enumerable.Empty<DrawableCarouselItem>();
 
@@ -37,12 +57,10 @@ namespace osu.Game.Screens.Select.Carousel
 
         private readonly Box hoverLayer;
 
-        protected override Container<Drawable> Content => nestedContainer;
+        protected Container<Drawable> Content => nestedContainer;
 
-        protected DrawableCarouselItem(CarouselItem item)
+        protected DrawableCarouselItem()
         {
-            Item = item;
-
             Height = MAX_HEIGHT;
             RelativeSizeAxes = Axes.X;
             Alpha = 0;
@@ -70,6 +88,7 @@ namespace osu.Game.Screens.Select.Carousel
         }
 
         private SampleChannel sampleHover;
+        private CarouselItem item;
 
         [BackgroundDependencyLoader]
         private void load(AudioManager audio, OsuColour colours)
@@ -98,14 +117,27 @@ namespace osu.Game.Screens.Select.Carousel
         {
             base.LoadComplete();
 
-            ApplyState();
+            UpdateItem();
-            Item.Filtered.ValueChanged += _ => Schedule(ApplyState);
-            Item.State.ValueChanged += _ => Schedule(ApplyState);
         }
 
+        protected virtual void UpdateItem()
+        {
+            if (item == null)
+                return;
+
+            ApplyState();
+
+            Item.Filtered.ValueChanged += onStateChange;
+            Item.State.ValueChanged += onStateChange;
+        }
+
+        private void onStateChange(ValueChangedEvent<CarouselItemState> obj) => Schedule(ApplyState);
+
+        private void onStateChange(ValueChangedEvent<bool> _) => Schedule(ApplyState);
+
         protected virtual void ApplyState()
         {
-            if (!IsLoaded) return;
+            Debug.Assert(Item != null);
 
             switch (Item.State.Value)
             {
@@ -126,6 +158,8 @@ namespace osu.Game.Screens.Select.Carousel
 
         protected virtual void Selected()
         {
+            Debug.Assert(Item != null);
+
             Item.State.Value = CarouselItemState.Selected;
 
             BorderContainer.BorderThickness = 2.5f;