Add a basic file selector with extension filtering support

osu.Game/Graphics/UserInterfaceV2/FileSelector.cs

@@ -0,0 +1,68 @@
+// 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 System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using osu.Framework.Allocation;
+using osu.Framework.Bindables;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Input.Events;
+
+namespace osu.Game.Graphics.UserInterfaceV2
+{
+    public class FileSelector : DirectorySelector
+    {
+        private readonly string[] validFileExtensions;
+
+        [Cached]
+        public readonly Bindable<FileInfo> CurrentFile = new Bindable<FileInfo>();
+
+        public FileSelector(string initialPath = null, string[] validFileExtensions = null)
+            : base(initialPath)
+        {
+            this.validFileExtensions = validFileExtensions ?? Array.Empty<string>();
+        }
+
+        protected override IEnumerable<DisplayPiece> GetEntriesForPath(DirectoryInfo path)
+        {
+            foreach (var dir in base.GetEntriesForPath(path))
+                yield return dir;
+
+            IEnumerable<FileInfo> files = path.GetFiles();
+
+            if (validFileExtensions.Length > 0)
+                files = files.Where(f => validFileExtensions.Contains(f.Extension));
+
+            foreach (var file in files.OrderBy(d => d.Name))
+            {
+                if ((file.Attributes & FileAttributes.Hidden) == 0)
+                    yield return new FilePiece(file);
+            }
+        }
+
+        protected class FilePiece : DisplayPiece
+        {
+            private readonly FileInfo file;
+
+            [Resolved]
+            private Bindable<FileInfo> currentFile { get; set; }
+
+            public FilePiece(FileInfo file)
+            {
+                this.file = file;
+            }
+
+            protected override bool OnClick(ClickEvent e)
+            {
+                currentFile.Value = file;
+                return true;
+            }
+
+            protected override string FallbackName => file.Name;
+
+            protected override IconUsage? Icon => FontAwesome.Regular.FileAudio;
+        }
+    }
+}