Add support for providing system file selector on iOS

osu.Framework.iOS/IOSFileSelector.cs

@@ -0,0 +1,71 @@
+// 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.IO;
+using System.Runtime.Versioning;
+using Foundation;
+using osu.Framework.Platform;
+using UIKit;
+using UniformTypeIdentifiers;
+
+namespace osu.Framework.iOS
+{
+    [SupportedOSPlatform("ios14.0")]
+    public class IOSFileSelector : UIDocumentPickerDelegate, ISystemFileSelector
+    {
+        public event Action<FileInfo>? Selected;
+
+        private readonly UIWindow window;
+
+        private readonly UIDocumentPickerViewController viewController;
+
+        public IOSFileSelector(UIWindow window, string[] allowedExtensions)
+        {
+            this.window = window;
+
+            UTType[] utTypes;
+
+            if (allowedExtensions.Length == 0)
+                utTypes = new[] { UTTypes.Data };
+            else
+            {
+                utTypes = new UTType[allowedExtensions.Length];
+
+                for (int i = 0; i < allowedExtensions.Length; i++)
+                {
+                    string extension = allowedExtensions[i];
+
+                    var type = UTType.CreateFromExtension(extension.Replace(".", string.Empty));
+                    if (type == null)
+                        throw new InvalidOperationException($"System failed to recognise extension \"{extension}\" when preparing the file selector.\n");
+
+                    utTypes[i] = type;
+                }
+            }
+
+            // files must be provided as copies, as they may be originally located in places that cannot be accessed freely (aka. iCloud Drive).
+            // we can acquire access to those files via startAccessingSecurityScopedResource but we must know when the game has finished using them.
+            // todo: refactor FileSelector/DirectorySelector to be aware when the game finished using a file/directory.
+            viewController = new UIDocumentPickerViewController(utTypes, true);
+            viewController.Delegate = this;
+        }
+
+        public void Present()
+        {
+            UIApplication.SharedApplication.InvokeOnMainThread(() =>
+            {
+                window.RootViewController!.PresentViewController(viewController, true, null);
+            });
+        }
+
+        public override void DidPickDocument(UIDocumentPickerViewController controller, NSUrl url)
+            => Selected?.Invoke(new FileInfo(url.Path!));
+
+        protected override void Dispose(bool disposing)
+        {
+            viewController.Dispose();
+            base.Dispose(disposing);
+        }
+    }
+}

osu.Framework.iOS/IOSGameHost.cs

@@ -23,6 +23,8 @@ namespace osu.Framework.iOS
 {
     public class IOSGameHost : SDLGameHost
     {
+        private IOSWindow iosWindow => (IOSWindow)Window;
+
         public IOSGameHost()
             : base(string.Empty)
         {
@@ -76,6 +78,23 @@ namespace osu.Framework.iOS
         public override VideoDecoder CreateVideoDecoder(Stream stream)
             => new IOSVideoDecoder(Renderer, stream);
 
+        public override ISystemFileSelector? CreateSystemFileSelector(string[] allowedExtensions)
+        {
+            IOSFileSelector? selector = null;
+
+            UIApplication.SharedApplication.InvokeOnMainThread(() =>
+            {
+                // creating UIDocumentPickerViewController programmatically is only supported on iOS 14.0+.
+                // on lower versions, return null and fall back to our normal file selector display.
+                if (!OperatingSystem.IsIOSVersionAtLeast(14))
+                    return;
+
+                selector = new IOSFileSelector(iosWindow.UIWindow, allowedExtensions);
+            });
+
+            return selector;
+        }
+
         public override IEnumerable<KeyBinding> PlatformKeyBindings => MacOSGameHost.KeyBindings;
     }
 }

osu.Framework.iOS/IOSWindow.cs

@@ -18,7 +18,9 @@ namespace osu.Framework.iOS
 {
     internal class IOSWindow : SDL3MobileWindow
     {
-        private UIWindow? window;
+        private UIWindow? uiWindow;
+
+        public UIWindow UIWindow => uiWindow!;
 
         public override Size Size
         {
@@ -27,7 +29,7 @@ namespace osu.Framework.iOS
             {
                 base.Size = value;
 
-                if (window != null)
+                if (uiWindow != null)
                     updateSafeArea();
             }
         }
@@ -43,7 +45,7 @@ namespace osu.Framework.iOS
 
             base.Create();
 
-            window = Runtime.GetNSObject<UIWindow>(WindowHandle);
+            uiWindow = Runtime.GetNSObject<UIWindow>(WindowHandle)!;
             updateSafeArea();
         }
 
@@ -73,14 +75,14 @@ namespace osu.Framework.iOS
 
         private void updateSafeArea()
         {
-            Debug.Assert(window != null);
+            Debug.Assert(uiWindow != null);
 
             SafeAreaPadding.Value = new MarginPadding
             {
-                Top = (float)window.SafeAreaInsets.Top * Scale,
-                Left = (float)window.SafeAreaInsets.Left * Scale,
-                Bottom = (float)window.SafeAreaInsets.Bottom * Scale,
-                Right = (float)window.SafeAreaInsets.Right * Scale,
+                Top = (float)uiWindow.SafeAreaInsets.Top * Scale,
+                Left = (float)uiWindow.SafeAreaInsets.Left * Scale,
+                Bottom = (float)uiWindow.SafeAreaInsets.Bottom * Scale,
+                Right = (float)uiWindow.SafeAreaInsets.Right * Scale,
             };
         }
     }