From 20e2e12dce2f81b92e8682f128cd81e08469f485 Mon Sep 17 00:00:00 2001
From: Stephane Delcroix <stephane@delcroix.org>
Date: Tue, 6 Dec 2016 13:15:32 +0100
Subject: [PATCH] [C] detach Behaviors and Triggers on VE finalization (#555)

* [C] detach Behaviors and Triggers on VE finalization

* update docs
---
 Xamarin.Forms.Core.UnitTests/BehaviorTest.cs       | 42 +++++++++++++++++++++-
 Xamarin.Forms.Core/BindableObject.cs               |  8 +++++
 Xamarin.Forms.Core/VisualElement.cs                | 13 +++++++
 .../Xamarin.Forms/VisualElement.xml                | 16 +++++++++
 4 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/Xamarin.Forms.Core.UnitTests/BehaviorTest.cs b/Xamarin.Forms.Core.UnitTests/BehaviorTest.cs
index 78e0cfb..9021738 100644
--- a/Xamarin.Forms.Core.UnitTests/BehaviorTest.cs
+++ b/Xamarin.Forms.Core.UnitTests/BehaviorTest.cs
@@ -3,8 +3,9 @@ using NUnit.Framework;
 
 namespace Xamarin.Forms.Core.UnitTests
 {
-	internal class MockBehavior<T> : Behavior<T> where T:BindableObject
+	class MockBehavior<T> : Behavior<T> where T:BindableObject
 	{
+		public static int AttachCount { get; set; }
 		public bool attached;
 		public bool detached;
 
@@ -12,11 +13,13 @@ namespace Xamarin.Forms.Core.UnitTests
 		{
 			base.OnAttachedTo (bindable);
 			attached = true;
+			AttachCount++;
 			AssociatedObject = bindable;
 		}
 
 		protected override void OnDetachingFrom (BindableObject bindable)
 		{
+			AttachCount--;
 			detached = true;
 			base.OnDetachingFrom (bindable);
 			AssociatedObject = null;
@@ -106,5 +109,42 @@ namespace Xamarin.Forms.Core.UnitTests
 			collection.Remove (behavior);
 			Assert.Null (behavior.AssociatedObject);
 		}
+
+		[Test]
+		//https://bugzilla.xamarin.com/show_bug.cgi?id=44074
+		public void TestBehaviorsAreDetachedBeforeGarbageCollection()
+		{
+			WeakReference weakBindable = null;
+
+			var attachCount = MockBehavior<VisualElement>.AttachCount;
+
+			int i = 0;
+			Action create = null;
+			create = () =>
+			{
+				if (i++ < 1024)
+				{
+					create();
+					return;
+				}
+
+				var bindable = new MockBindable
+				{
+					Behaviors = {
+						new MockBehavior<VisualElement> ()
+					}
+				};
+				weakBindable = new WeakReference(bindable);
+			};
+
+			create();
+
+			GC.Collect();
+			GC.WaitForPendingFinalizers();
+			GC.Collect();
+
+			Assert.False(weakBindable.IsAlive);
+			Assert.AreEqual(attachCount, MockBehavior<VisualElement>.AttachCount);
+		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/BindableObject.cs b/Xamarin.Forms.Core/BindableObject.cs
index 217f4a9..b5e4145 100644
--- a/Xamarin.Forms.Core/BindableObject.cs
+++ b/Xamarin.Forms.Core/BindableObject.cs
@@ -163,6 +163,14 @@ namespace Xamarin.Forms
 			return bpcontext != null && bpcontext.Binding != null;
 		}
 
+		internal bool GetIsDefault(BindableProperty targetProperty)
+		{
+			if (targetProperty == null)
+				throw new ArgumentNullException(nameof(targetProperty));
+
+			return GetContext(targetProperty) == null;
+		}
+
 		internal object[] GetValues(BindableProperty property0, BindableProperty property1)
 		{
 			var values = new object[2];
diff --git a/Xamarin.Forms.Core/VisualElement.cs b/Xamarin.Forms.Core/VisualElement.cs
index 053ddb0..cff1eb1 100644
--- a/Xamarin.Forms.Core/VisualElement.cs
+++ b/Xamarin.Forms.Core/VisualElement.cs
@@ -781,5 +781,18 @@ namespace Xamarin.Forms
 
 			public bool Result { get; set; }
 		}
+
+		~VisualElement()
+		{
+			if (!GetIsDefault(BehaviorsProperty)) {
+				var behaviors = GetValue(BehaviorsProperty) as AttachedCollection<Behavior>;
+				behaviors.DetachFrom(this);
+			}
+
+			if (!GetIsDefault(TriggersProperty)) {
+				var triggers = GetValue(TriggersProperty) as AttachedCollection<Trigger>;
+				triggers.DetachFrom(this);
+			}
+		}
 	}
 }
\ No newline at end of file
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms/VisualElement.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms/VisualElement.xml
index 426d8c6..9b28bf0 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms/VisualElement.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms/VisualElement.xml
@@ -290,6 +290,22 @@
         </remarks>
       </Docs>
     </Member>
+    <Member MemberName="Finalize">
+      <MemberSignature Language="C#" Value="~VisualElement ();" />
+      <MemberSignature Language="ILAsm" Value=".method familyhidebysig virtual instance void Finalize() cil managed" />
+      <MemberType>Method</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>System.Void</ReturnType>
+      </ReturnValue>
+      <Parameters />
+      <Docs>
+        <summary>To be added.</summary>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
     <Member MemberName="Focus">
       <MemberSignature Language="C#" Value="public bool Focus ();" />
       <MemberSignature Language="ILAsm" Value=".method public hidebysig instance bool Focus() cil managed" />
-- 
2.7.4