From 1f46076f16deb2e0a60146b41b3fa01586b6c0d6 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Thu, 9 Jan 2020 10:35:15 +0100
Subject: [PATCH] Use NonVirtualizingLayoutContext.

- Add and use `NonVirtualizingLayoutContext` in `NonVirtualizingLayout`
- Return -1 instead of throwing if element is not a child of `ItemsRepeater`

Ported from https://github.com/microsoft/microsoft-ui-xaml/commit/22adf4dc624baf339a1da3f9c7d83e125f2f1b01
---
 src/Avalonia.Controls/Repeater/ViewManager.cs       |  3 ++-
 src/Avalonia.Layout/NonVirtualizingLayout.cs        |  8 ++++----
 src/Avalonia.Layout/NonVirtualizingLayoutContext.cs | 11 +++++++++++
 3 files changed, 17 insertions(+), 5 deletions(-)
 create mode 100644 src/Avalonia.Layout/NonVirtualizingLayoutContext.cs

diff --git a/src/Avalonia.Controls/Repeater/ViewManager.cs b/src/Avalonia.Controls/Repeater/ViewManager.cs
index f4588787e8..d670aa077c 100644
--- a/src/Avalonia.Controls/Repeater/ViewManager.cs
+++ b/src/Avalonia.Controls/Repeater/ViewManager.cs
@@ -200,7 +200,8 @@ namespace Avalonia.Controls
         {
             if (virtInfo == null)
             {
-                throw new ArgumentException("Element is not a child of this ItemsRepeater.");
+                //Element is not a child of this ItemsRepeater.
+                return -1;
             }
 
             return virtInfo.IsRealized || virtInfo.IsInUniqueIdResetPool ? virtInfo.Index : -1;
diff --git a/src/Avalonia.Layout/NonVirtualizingLayout.cs b/src/Avalonia.Layout/NonVirtualizingLayout.cs
index fba91e66c7..3917830eb7 100644
--- a/src/Avalonia.Layout/NonVirtualizingLayout.cs
+++ b/src/Avalonia.Layout/NonVirtualizingLayout.cs
@@ -32,7 +32,7 @@ namespace Avalonia.Layout
         /// <inheritdoc/>
         public sealed override Size Measure(LayoutContext context, Size availableSize)
         {
-            return MeasureOverride((VirtualizingLayoutContext)context, availableSize);
+            return MeasureOverride((NonVirtualizingLayoutContext)context, availableSize);
         }
 
         /// <inheritdoc/>
@@ -49,7 +49,7 @@ namespace Avalonia.Layout
         /// The context object that facilitates communication between the layout and its host
         /// container.
         /// </param>
-        protected virtual void InitializeForContextCore(VirtualizingLayoutContext context)
+        protected virtual void InitializeForContextCore(LayoutContext context)
         {
         }
 
@@ -61,7 +61,7 @@ namespace Avalonia.Layout
         /// The context object that facilitates communication between the layout and its host
         /// container.
         /// </param>
-        protected virtual void UninitializeForContextCore(VirtualizingLayoutContext context)
+        protected virtual void UninitializeForContextCore(LayoutContext context)
         {
         }
 
@@ -83,7 +83,7 @@ namespace Avalonia.Layout
         /// of the allocated sizes for child objects or based on other considerations such as a
         /// fixed container size.
         /// </returns>
-        protected abstract Size MeasureOverride(VirtualizingLayoutContext context, Size availableSize);
+        protected abstract Size MeasureOverride(NonVirtualizingLayoutContext context, Size availableSize);
 
         /// <summary>
         /// When implemented in a derived class, provides the behavior for the "Arrange" pass of
diff --git a/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs b/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs
new file mode 100644
index 0000000000..201ffa7d36
--- /dev/null
+++ b/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs
@@ -0,0 +1,11 @@
+// This source file is adapted from the WinUI project.
+// (https://github.com/microsoft/microsoft-ui-xaml)
+//
+// Licensed to The Avalonia Project under MIT License, courtesy of The .NET Foundation.
+
+namespace Avalonia.Layout
+{
+    public abstract class NonVirtualizingLayoutContext : LayoutContext
+    {
+    }
+}