Split OnlinePlayComposite to remove if-statement

osu.Game/Screens/OnlinePlay/Multiplayer/Match/BeatmapSelectionControl.cs

@@ -11,7 +11,7 @@ using osu.Game.Screens.OnlinePlay.Match.Components;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
 {
-    public class BeatmapSelectionControl : OnlinePlayComposite
+    public class BeatmapSelectionControl : RoomSubScreenComposite
     {
         [Resolved]
         private MultiplayerMatchSubScreen matchSubScreen { get; set; }

osu.Game/Screens/OnlinePlay/OnlinePlayComposite.cs

@@ -2,9 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using System.Collections.Specialized;
 using System.Linq;
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics.Containers;
@@ -14,6 +12,9 @@ using osu.Game.Users;
 
 namespace osu.Game.Screens.OnlinePlay
 {
+    /// <summary>
+    /// A <see cref="CompositeDrawable"/> that exposes bindables for <see cref="Room"/> properties.
+    /// </summary>
     public class OnlinePlayComposite : CompositeDrawable
     {
         [Resolved(typeof(Room))]
@@ -62,41 +63,18 @@ namespace osu.Game.Screens.OnlinePlay
         /// The currently selected item in the <see cref="RoomSubScreen"/>, or the first item from <see cref="Playlist"/>
         /// if this <see cref="OnlinePlayComposite"/> is not within a <see cref="RoomSubScreen"/>.
         /// </summary>
-        protected IBindable<PlaylistItem> SelectedItem => selectedItem;
+        protected readonly Bindable<PlaylistItem> SelectedItem = new Bindable<PlaylistItem>();
-
-        private readonly Bindable<PlaylistItem> selectedItem = new Bindable<PlaylistItem>();
-
-        [CanBeNull]
-        [Resolved(CanBeNull = true)]
-        private IBindable<PlaylistItem> subScreenSelectedItem { get; set; }
 
         protected override void LoadComplete()
         {
             base.LoadComplete();
 
-            if (subScreenSelectedItem != null)
+            Playlist.BindCollectionChanged((_, __) => UpdateSelectedItem(), true);
-                subScreenSelectedItem.BindValueChanged(onSelectedItemChanged, true);
-            else
-                Playlist.BindCollectionChanged(onPlaylistChanged, true);
         }
 
-        /// <summary>
+        protected virtual void UpdateSelectedItem()
-        /// Invoked when the selected item from within a <see cref="RoomSubScreen"/> changes.
-        /// Does not occur when this <see cref="OnlinePlayComposite"/> is outside a <see cref="RoomSubScreen"/>.
-        /// </summary>
-        private void onSelectedItemChanged(ValueChangedEvent<PlaylistItem> item)
         {
-            // If the room hasn't been created yet, fall-back to the first item from the playlist.
+            SelectedItem.Value = Playlist.FirstOrDefault();
-            selectedItem.Value = RoomID.Value == null ? Playlist.FirstOrDefault() : item.NewValue;
-        }
-
-        /// <summary>
-        /// Invoked when the playlist changes.
-        /// Does not occur when this <see cref="OnlinePlayComposite"/> is inside a <see cref="RoomSubScreen"/>.
-        /// </summary>
-        private void onPlaylistChanged(object sender, NotifyCollectionChangedEventArgs e)
-        {
-            selectedItem.Value = Playlist.FirstOrDefault();
         }
     }
 }

osu.Game/Screens/OnlinePlay/RoomSubScreenComposite.cs

@@ -0,0 +1,38 @@
+// 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 osu.Framework.Allocation;
+using osu.Framework.Bindables;
+using osu.Game.Online.Rooms;
+using osu.Game.Screens.OnlinePlay.Match;
+
+namespace osu.Game.Screens.OnlinePlay
+{
+    /// <summary>
+    /// An <see cref="OnlinePlayComposite"/> with additional logic tracking the currently-selected <see cref="PlaylistItem"/> inside a <see cref="RoomSubScreen"/>.
+    /// </summary>
+    public class RoomSubScreenComposite : OnlinePlayComposite
+    {
+        [Resolved]
+        private IBindable<PlaylistItem> subScreenSelectedItem { get; set; }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            subScreenSelectedItem.BindValueChanged(_ => UpdateSelectedItem(), true);
+        }
+
+        protected override void UpdateSelectedItem()
+        {
+            if (RoomID.Value == null)
+            {
+                // If the room hasn't been created yet, fall-back to the base logic.
+                base.UpdateSelectedItem();
+                return;
+            }
+
+            SelectedItem.Value = subScreenSelectedItem.Value;
+        }
+    }
+}