From 24c5519e7199f9b7631c25d7b75876ee69669aec Mon Sep 17 00:00:00 2001
From: Dariusz Komosinski <darek.komosinski@gmail.com>
Date: Sat, 7 Dec 2019 18:31:19 +0100
Subject: [PATCH] Use CondtionalWeakTable to avoid FocusManager becoming a GC
 root for all focus scopes.

---
 src/Avalonia.Input/FocusManager.cs | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/Avalonia.Input/FocusManager.cs b/src/Avalonia.Input/FocusManager.cs
index 77902a7390..a9ce8ee494 100644
--- a/src/Avalonia.Input/FocusManager.cs
+++ b/src/Avalonia.Input/FocusManager.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using Avalonia.Interactivity;
 using Avalonia.VisualTree;
 
@@ -17,8 +18,8 @@ namespace Avalonia.Input
         /// <summary>
         /// The focus scopes in which the focus is currently defined.
         /// </summary>
-        private readonly Dictionary<IFocusScope, IInputElement> _focusScopes =
-            new Dictionary<IFocusScope, IInputElement>();
+        private readonly ConditionalWeakTable<IFocusScope, IInputElement> _focusScopes =
+            new ConditionalWeakTable<IFocusScope, IInputElement>();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FocusManager"/> class.
@@ -110,7 +111,18 @@ namespace Avalonia.Input
         {
             Contract.Requires<ArgumentNullException>(scope != null);
 
-            _focusScopes[scope] = element;
+            if (_focusScopes.TryGetValue(scope, out IInputElement existingElement))
+            {
+                if (element != existingElement)
+                {
+                    _focusScopes.Remove(scope);
+                    _focusScopes.Add(scope, element);
+                }
+            }
+            else
+            {
+                _focusScopes.Add(scope, element);
+            }
 
             if (Scope == scope)
             {