1 files changed, 127 insertions, 0 deletions
diff --git a/Xamarin.Forms.Core/Interactivity/AttachedCollection.cs b/Xamarin.Forms.Core/Interactivity/AttachedCollection.cs
new file mode 100644
index 00000000..6aff5147
--- /dev/null
+++ b/Xamarin.Forms.Core/Interactivity/AttachedCollection.cs
@@ -0,0 +1,127 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+
+namespace Xamarin.Forms
+{
+	internal class AttachedCollection<T> : ObservableCollection<T>, ICollection<T>, IAttachedObject where T : BindableObject, IAttachedObject
+	{
+		readonly List<WeakReference> _associatedObjects = new List<WeakReference>();
+
+		public AttachedCollection()
+		{
+		}
+
+		public AttachedCollection(IEnumerable<T> collection) : base(collection)
+		{
+		}
+
+		public AttachedCollection(IList<T> list) : base(list)
+		{
+		}
+
+		public void AttachTo(BindableObject bindable)
+		{
+			if (bindable == null)
+				throw new ArgumentNullException("bindable");
+			OnAttachedTo(bindable);
+		}
+
+		public void DetachFrom(BindableObject bindable)
+		{
+			OnDetachingFrom(bindable);
+		}
+
+		protected override void ClearItems()
+		{
+			foreach (WeakReference weakbindable in _associatedObjects)
+			{
+				foreach (T item in this)
+				{
+					var bindable = weakbindable.Target as BindableObject;
+					if (bindable == null)
+						continue;
+					item.DetachFrom(bindable);
+				}
+			}
+			base.ClearItems();
+		}
+
+		protected override void InsertItem(int index, T item)
+		{
+			base.InsertItem(index, item);
+			foreach (WeakReference weakbindable in _associatedObjects)
+			{
+				var bindable = weakbindable.Target as BindableObject;
+				if (bindable == null)
+					continue;
+				item.AttachTo(bindable);
+			}
+		}
+
+		protected virtual void OnAttachedTo(BindableObject bindable)
+		{
+			lock(_associatedObjects)
+			{
+				_associatedObjects.Add(new WeakReference(bindable));
+			}
+			foreach (T item in this)
+				item.AttachTo(bindable);
+		}
+
+		protected virtual void OnDetachingFrom(BindableObject bindable)
+		{
+			foreach (T item in this)
+				item.DetachFrom(bindable);
+			lock(_associatedObjects)
+			{
+				for (var i = 0; i < _associatedObjects.Count; i++)
+				{
+					object target = _associatedObjects[i].Target;
+
+					if (target == null || target == bindable)
+					{
+						_associatedObjects.RemoveAt(i);
+						i--;
+					}
+				}
+			}
+		}
+
+		protected override void RemoveItem(int index)
+		{
+			T item = this[index];
+			foreach (WeakReference weakbindable in _associatedObjects)
+			{
+				var bindable = weakbindable.Target as BindableObject;
+				if (bindable == null)
+					continue;
+				item.DetachFrom(bindable);
+			}
+
+			base.RemoveItem(index);
+		}
+
+		protected override void SetItem(int index, T item)
+		{
+			T old = this[index];
+			foreach (WeakReference weakbindable in _associatedObjects)
+			{
+				var bindable = weakbindable.Target as BindableObject;
+				if (bindable == null)
+					continue;
+				old.DetachFrom(bindable);
+			}
+
+			base.SetItem(index, item);
+
+			foreach (WeakReference weakbindable in _associatedObjects)
+			{
+				var bindable = weakbindable.Target as BindableObject;
+				if (bindable == null)
+					continue;
+				item.AttachTo(bindable);
+			}
+		}
+	}
+}
+\ No newline at end of file