[iOS] Keep our native property listener around the same time we keep our proxy, check if we are KVO compliant before adding observer (#403)

2 files changed, 27 insertions, 3 deletions

diff --git a/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs b/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
index eab88e81..4c3eed98 100644
--- a/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
+++ b/Xamarin.Forms.Platform.iOS/Extensions/UIViewExtensions.cs
@@ -37,9 +37,31 @@ namespace Xamarin.Forms.Platform.iOS
 			}
 
 			NativeViewPropertyListener nativePropertyListener = null;
-			if (bindingBase.Mode == BindingMode.TwoWay) {
+			if (bindingBase.Mode == BindingMode.TwoWay)
+			{
 				nativePropertyListener = new NativeViewPropertyListener(propertyName);
-				view.AddObserver(nativePropertyListener, propertyName, 0, IntPtr.Zero);
+				try
+				{
+					//TODO: We need to figure a way to map the value back to the real objectiveC property.
+					//the X.IOS camelcase property name won't work
+					var key = new Foundation.NSString(propertyName.ToLower());
+					var valueKey = view.ValueForKey(key);
+					if (valueKey != null)
+					{
+						view.AddObserver(nativePropertyListener, key, Foundation.NSKeyValueObservingOptions.New, IntPtr.Zero);
+					}
+				}
+				catch (Foundation.MonoTouchException ex)
+				{
+					nativePropertyListener = null;
+					if (ex.Name == "NSUnknownKeyException")
+					{
+						System.Diagnostics.Debug.WriteLine("KVO not supported, try specify a UpdateSourceEventName instead.");
+						return;
+					}
+					throw ex;
+				}
+
 			}
 
 			NativeBindingHelpers.SetBinding(view, propertyName, bindingBase, nativePropertyListener);
diff --git a/Xamarin.Forms.Platform.iOS/NativeViewPropertyListener.cs b/Xamarin.Forms.Platform.iOS/NativeViewPropertyListener.cs
index 2d872af2..4e6601ef 100644
--- a/Xamarin.Forms.Platform.iOS/NativeViewPropertyListener.cs
+++ b/Xamarin.Forms.Platform.iOS/NativeViewPropertyListener.cs
@@ -17,8 +17,10 @@ namespace Xamarin.Forms.Platform.iOS
 
 		public override void ObserveValue(NSString keyPath, NSObject ofObject, NSDictionary change, IntPtr context)
 		{
-			if (keyPath == TargetProperty)
+			if (keyPath.ToString().Equals(TargetProperty, StringComparison.InvariantCultureIgnoreCase))
 				PropertyChanged?.Invoke(ofObject, new PropertyChangedEventArgs(TargetProperty));
+			else
+				base.ObserveValue(keyPath, ofObject, change, context);
 		}
 	}
 }