1 files changed, 111 insertions, 0 deletions
diff --git a/Xamarin.Forms.Core/BindingBase.cs b/Xamarin.Forms.Core/BindingBase.cs
new file mode 100644
index 00000000..0810cbcf
--- /dev/null
+++ b/Xamarin.Forms.Core/BindingBase.cs
@@ -0,0 +1,111 @@
+using System;
+using System.Collections;
+using System.Runtime.CompilerServices;
+
+namespace Xamarin.Forms
+{
+	public abstract class BindingBase
+	{
+		static readonly ConditionalWeakTable<IEnumerable, CollectionSynchronizationContext> SynchronizedCollections = new ConditionalWeakTable<IEnumerable, CollectionSynchronizationContext>();
+
+		BindingMode _mode = BindingMode.Default;
+		string _stringFormat;
+
+		internal BindingBase()
+		{
+		}
+
+		public BindingMode Mode
+		{
+			get { return _mode; }
+			set
+			{
+				if (value != BindingMode.Default && value != BindingMode.OneWay && value != BindingMode.OneWayToSource && value != BindingMode.TwoWay)
+					throw new ArgumentException("mode is not a valid BindingMode", "mode");
+
+				ThrowIfApplied();
+
+				_mode = value;
+			}
+		}
+
+		public string StringFormat
+		{
+			get { return _stringFormat; }
+			set
+			{
+				ThrowIfApplied();
+
+				_stringFormat = value;
+			}
+		}
+
+		internal bool AllowChaining { get; set; }
+
+		internal object Context { get; set; }
+
+		internal bool IsApplied { get; private set; }
+
+		public static void DisableCollectionSynchronization(IEnumerable collection)
+		{
+			if (collection == null)
+				throw new ArgumentNullException("collection");
+
+			SynchronizedCollections.Remove(collection);
+		}
+
+		public static void EnableCollectionSynchronization(IEnumerable collection, object context, CollectionSynchronizationCallback callback)
+		{
+			if (collection == null)
+				throw new ArgumentNullException("collection");
+			if (callback == null)
+				throw new ArgumentNullException("callback");
+
+			SynchronizedCollections.Add(collection, new CollectionSynchronizationContext(context, callback));
+		}
+
+		protected void ThrowIfApplied()
+		{
+			if (IsApplied)
+				throw new InvalidOperationException("Can not change a binding while it's applied");
+		}
+
+		internal virtual void Apply(bool fromTarget)
+		{
+			IsApplied = true;
+		}
+
+		internal virtual void Apply(object context, BindableObject bindObj, BindableProperty targetProperty)
+		{
+			IsApplied = true;
+		}
+
+		internal abstract BindingBase Clone();
+
+		internal virtual object GetSourceValue(object value, Type targetPropertyType)
+		{
+			if (StringFormat != null)
+				return string.Format(StringFormat, value);
+
+			return value;
+		}
+
+		internal virtual object GetTargetValue(object value, Type sourcePropertyType)
+		{
+			return value;
+		}
+
+		internal static bool TryGetSynchronizedCollection(IEnumerable collection, out CollectionSynchronizationContext synchronizationContext)
+		{
+			if (collection == null)
+				throw new ArgumentNullException("collection");
+
+			return SynchronizedCollections.TryGetValue(collection, out synchronizationContext);
+		}
+
+		internal virtual void Unapply()
+		{
+			IsApplied = false;
+		}
+	}
+}
+\ No newline at end of file