From 474aa60403eda89401e078fe6e453c2940fad9a4 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Fri, 4 Aug 2017 20:03:33 +0200
Subject: [PATCH] Don't remove pseudoclasses when clearing Classes.

Fixes #1080
---
 src/Avalonia.Base/Collections/AvaloniaList.cs     |  2 +-
 src/Avalonia.Controls/Classes.cs                  | 14 ++++++++++++++
 tests/Avalonia.Controls.UnitTests/ClassesTests.cs | 12 ++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Collections/AvaloniaList.cs b/src/Avalonia.Base/Collections/AvaloniaList.cs
index ace898b55f..a3c3015a38 100644
--- a/src/Avalonia.Base/Collections/AvaloniaList.cs
+++ b/src/Avalonia.Base/Collections/AvaloniaList.cs
@@ -220,7 +220,7 @@ namespace Avalonia.Collections
         /// <summary>
         /// Removes all items from the collection.
         /// </summary>
-        public void Clear()
+        public virtual void Clear()
         {
             if (this.Count > 0)
             {
diff --git a/src/Avalonia.Controls/Classes.cs b/src/Avalonia.Controls/Classes.cs
index 02fd6e63bf..c897e86697 100644
--- a/src/Avalonia.Controls/Classes.cs
+++ b/src/Avalonia.Controls/Classes.cs
@@ -86,6 +86,20 @@ namespace Avalonia.Controls
             base.AddRange(c);
         }
 
+        /// <summary>
+        /// Remvoes all non-pseudoclasses from the collection.
+        /// </summary>
+        public override void Clear()
+        {
+            for (var i = Count - 1; i >= 0; --i)
+            {
+                if (!this[i].StartsWith(":"))
+                {
+                    RemoveAt(i);
+                }
+            }
+        }
+
         /// <summary>
         /// Inserts a style class into the collection.
         /// </summary>
diff --git a/tests/Avalonia.Controls.UnitTests/ClassesTests.cs b/tests/Avalonia.Controls.UnitTests/ClassesTests.cs
index fae97bada7..c9b9d9f82c 100644
--- a/tests/Avalonia.Controls.UnitTests/ClassesTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ClassesTests.cs
@@ -149,5 +149,17 @@ namespace Avalonia.Controls.UnitTests
 
             Assert.Throws<ArgumentException>(() => target.Replace(new[] { ":qux" }));
         }
+
+        [Fact]
+        public void Clear_Should_Not_Remove_Pseudoclasses()
+        {
+            var target = new Classes("foo", "bar");
+
+            ((IPseudoClasses)target).Add(":baz");
+
+            target.Clear();
+
+            Assert.Equal(new[] { ":baz" }, target);
+        }
     }
 }