Ported IElementFactory from UWP/WinUI.

src/Avalonia.Controls/Repeater/IElementFactory.cs

@@ -0,0 +1,66 @@
+using Avalonia.Controls.Templates;
+
+namespace Avalonia.Controls
+{
+    /// <summary>
+    /// Represents the optional arguments to use when calling an implementation of the
+    /// <see cref="IElementFactory"/>'s <see cref="IElementFactory.GetElement"/> method.
+    /// </summary>
+    public class ElementFactoryGetArgs
+    {
+        /// <summary>
+        /// Gets or sets the data item for which an appropriate element tree should be realized
+        /// when calling <see cref="IElementFactory.GetElement"/>.
+        /// </summary>
+        public object Data { get; set; }
+
+        /// <summary>
+        /// Gets or sets the <see cref="IControl"/> that is expected to be the parent of the
+        /// realized element from <see cref="IElementFactory.GetElement"/>.
+        /// </summary>
+        public IControl Parent { get; set; }
+
+        /// <summary>
+        /// Gets or sets the index of the item that should be realized.
+        /// </summary>
+        public int Index { get; set; }
+    }
+
+    /// <summary>
+    /// Represents the optional arguments to use when calling an implementation of the
+    /// <see cref="IElementFactory"/>'s <see cref="IElementFactory.GetElement"/> method.
+    /// </summary>
+    public class ElementFactoryRecycleArgs
+    {
+        /// <summary>
+        /// Gets or sets the <see cref="IControl"/> to recycle when calling 
+        /// <see cref="IElementFactory.RecycleElement"/>.
+        /// </summary>
+        public IControl Element { get; set; }
+
+        /// <summary>
+        /// Gets or sets the <see cref="IControl"/> that is expected to be the parent of the
+        /// realized element from <see cref="IElementFactory.GetElement"/>.
+        /// </summary>
+        public IControl Parent { get; set; }
+    }
+
+    /// <summary>
+    /// A data template that supports creating and recyling elements for an <see cref="ItemsRepeater"/>.
+    /// </summary>
+    public interface IElementFactory : IDataTemplate
+    {
+        /// <summary>
+        /// Gets an <see cref="IControl"/>.
+        /// </summary>
+        /// <param name="args">The element args.</param>
+        public IControl GetElement(ElementFactoryGetArgs args);
+
+        /// <summary>
+        /// Recycles an <see cref="IControl"/> that was previously retrieved using
+        /// <see cref="GetElement"/>.
+        /// </summary>
+        /// <param name="args">The recycle args.</param>
+        public void RecycleElement(ElementFactoryRecycleArgs args);
+    }
+}

src/Avalonia.Controls/Repeater/ItemTemplateWrapper.cs

@@ -7,13 +7,27 @@ using Avalonia.Controls.Templates;
 
 namespace Avalonia.Controls
 {
-    internal class ItemTemplateWrapper
+    internal class ItemTemplateWrapper : IElementFactory
     {
         private readonly IDataTemplate _dataTemplate;
 
         public ItemTemplateWrapper(IDataTemplate dataTemplate) => _dataTemplate = dataTemplate;
 
-        public IControl GetElement(IControl parent, object data)
+        public bool SupportsRecycling => false;
+        public IControl Build(object param) => GetElement(null, param);
+        public bool Match(object data) => _dataTemplate.Match(data);
+
+        public IControl GetElement(ElementFactoryGetArgs args)
+        {
+            return GetElement(args.Parent, args.Data);
+        }
+
+        public void RecycleElement(ElementFactoryRecycleArgs args)
+        {
+            RecycleElement(args.Parent, args.Element);
+        }
+
+        private IControl GetElement(IControl parent, object data)
         {
             var selectedTemplate = _dataTemplate;
             var recyclePool = RecyclePool.GetPoolInstance(selectedTemplate);
@@ -37,7 +51,7 @@ namespace Avalonia.Controls
             return element;
         }
 
-        public void RecycleElement(IControl parent, IControl element)
+        private void RecycleElement(IControl parent, IControl element)
         {
             var selectedTemplate = _dataTemplate;
             var recyclePool = RecyclePool.GetPoolInstance(selectedTemplate);

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -141,7 +141,7 @@ namespace Avalonia.Controls
         /// </summary>
         public ItemsSourceView ItemsSourceView { get; private set; }
 
-        internal ItemTemplateWrapper ItemTemplateShim { get; set; }
+        internal IElementFactory ItemTemplateShim { get; set; }
         internal Point LayoutOrigin { get; set; }
         internal object LayoutState { get; set; }
         internal IControl MadeAnchor => _viewportManager.MadeAnchor;
@@ -664,7 +664,7 @@ namespace Avalonia.Controls
                 }
             }
 
-            ItemTemplateShim = new ItemTemplateWrapper(newValue);
+            ItemTemplateShim = newValue as IElementFactory ?? new ItemTemplateWrapper(newValue);
 
             InvalidateMeasure();
         }

src/Avalonia.Controls/Repeater/ViewManager.cs

@@ -6,11 +6,9 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Specialized;
-using System.Linq;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Interactivity;
-using Avalonia.Layout;
 using Avalonia.Logging;
 using Avalonia.VisualTree;
 
@@ -26,6 +24,8 @@ namespace Avalonia.Controls
         private readonly UniqueIdElementPool _resetPool;
         private IControl _lastFocusedElement;
         private bool _isDataSourceStableResetPending;
+        private ElementFactoryGetArgs _elementFactoryGetArgs;
+        private ElementFactoryRecycleArgs _elementFactoryRecycleArgs;
         private int _firstRealizedElementIndexHeldByLayout = FirstRealizedElementIndexDefault;
         private int _lastRealizedElementIndexHeldByLayout = LastRealizedElementIndexDefault;
         private bool _eventsSubscribed;
@@ -134,7 +134,14 @@ namespace Avalonia.Controls
 
             if (_owner.ItemTemplateShim != null)
             {
-                _owner.ItemTemplateShim.RecycleElement(_owner, element);
+                var context = _elementFactoryRecycleArgs ??= new ElementFactoryRecycleArgs();
+                context.Element = element;
+                context.Parent = _owner;
+
+                _owner.ItemTemplateShim.RecycleElement(context);
+
+                context.Element = null;
+                context.Parent = null;
             }
             else
             {
@@ -579,7 +586,7 @@ namespace Avalonia.Controls
             var data = _owner.ItemsSourceView.GetAt(index);
             var providedElementFactory = _owner.ItemTemplateShim;
 
-            ItemTemplateWrapper GetElementFactory()
+            IElementFactory GetElementFactory()
             {
                 if (providedElementFactory == null)
                 {
@@ -602,7 +609,20 @@ namespace Avalonia.Controls
                 }
 
                 var elementFactory = GetElementFactory();
-                return elementFactory.GetElement(_owner, data);
+                var args = _elementFactoryGetArgs ??= new ElementFactoryGetArgs();
+
+                try
+                {
+                    args.Data = data;
+                    args.Parent = _owner;
+                    args.Index = index;
+                    return elementFactory.GetElement(args);
+                }
+                finally
+                {
+                    args.Data = null;
+                    args.Parent = null;
+                }
             }
 
             var element = GetElement();
@@ -732,6 +752,7 @@ namespace Avalonia.Controls
             {
                 _owner.GotFocus += OnFocusChanged;
                 _owner.LostFocus += OnFocusChanged;
+                _eventsSubscribed = true;
             }
         }