Native Bindings (#278)

* [C, I, A, W] Support Native Bindings

* fix tabs

3 files changed, 202 insertions, 1 deletions

diff --git a/Xamarin.Forms.Core/Binding.cs b/Xamarin.Forms.Core/Binding.cs
index 5fa1dd65..b3baa0df 100644
--- a/Xamarin.Forms.Core/Binding.cs
+++ b/Xamarin.Forms.Core/Binding.cs
@@ -17,6 +17,7 @@ namespace Xamarin.Forms
 		BindingExpression _expression;
 		string _path;
 		object _source;
+		string _updateSourceEventName;
 
 		public Binding()
 		{
@@ -81,6 +82,14 @@ namespace Xamarin.Forms
 			}
 		}
 
+		internal string UpdateSourceEventName {
+			get { return _updateSourceEventName; }
+			set {
+				ThrowIfApplied();
+				_updateSourceEventName = value;
+			}
+		}
+
 		public static Binding Create<TSource>(Expression<Func<TSource, object>> propertyGetter, BindingMode mode = BindingMode.Default, IValueConverter converter = null, object converterParameter = null,
 											  string stringFormat = null)
 		{
@@ -115,7 +124,7 @@ namespace Xamarin.Forms
 
 		internal override BindingBase Clone()
 		{
-			return new Binding(Path, Mode) { Converter = Converter, ConverterParameter = ConverterParameter, StringFormat = StringFormat, Source = Source };
+			return new Binding(Path, Mode) { Converter = Converter, ConverterParameter = ConverterParameter, StringFormat = StringFormat, Source = Source, UpdateSourceEventName = UpdateSourceEventName };
 		}
 
 		internal override object GetSourceValue(object value, Type targetPropertyType)
diff --git a/Xamarin.Forms.Core/NativeBindingHelpers.cs b/Xamarin.Forms.Core/NativeBindingHelpers.cs
new file mode 100644
index 00000000..c732efd5
--- /dev/null
+++ b/Xamarin.Forms.Core/NativeBindingHelpers.cs
@@ -0,0 +1,191 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using Xamarin.Forms.Internals;
+
+using static System.String;
+
+namespace Xamarin.Forms
+{
+	static class NativeBindingHelpers
+	{
+		public static void SetBinding<TNativeView>(TNativeView target, string targetProperty, BindingBase bindingBase, string updateSourceEventName=null) where TNativeView : class
+		{
+			var binding = bindingBase as Binding;
+			//This will allow setting bindings from Xaml by reusing the MarkupExtension
+			if (IsNullOrEmpty(updateSourceEventName) && binding != null && !IsNullOrEmpty(binding.UpdateSourceEventName))
+				updateSourceEventName = binding.UpdateSourceEventName;
+			INotifyPropertyChanged eventWrapper = null;
+			if (!IsNullOrEmpty(updateSourceEventName))
+				eventWrapper = new EventWrapper(target, targetProperty, updateSourceEventName);
+
+			SetBinding(target, targetProperty, bindingBase, eventWrapper);
+		}
+
+		internal static void SetBinding<TNativeView>(TNativeView target, string targetProperty, BindingBase bindingBase, INotifyPropertyChanged propertyChanged) where TNativeView : class
+		{
+			if (target == null)
+				throw new ArgumentNullException(nameof(target));
+			if (IsNullOrEmpty(targetProperty))
+				throw new ArgumentNullException(nameof(targetProperty));
+
+			var binding = bindingBase as Binding;
+			var proxy = BindableObjectProxy<TNativeView>.BindableObjectProxies.GetValue(target, (TNativeView key) => new BindableObjectProxy<TNativeView>(key));
+			BindableProperty bindableProperty = null;
+			propertyChanged = propertyChanged ?? target as INotifyPropertyChanged;
+			bindableProperty = CreateBindableProperty<TNativeView>(targetProperty);
+			if (binding != null && binding.Mode != BindingMode.OneWay && propertyChanged != null)
+				propertyChanged.PropertyChanged += (sender, e) => {
+					if (e.PropertyName != targetProperty)
+						return;
+				SetValueFromNative<TNativeView>(sender as TNativeView, targetProperty, bindableProperty);
+			};
+
+			if (binding != null && binding.Mode != BindingMode.OneWay)
+				SetValueFromNative(target, targetProperty, bindableProperty);
+
+			proxy.SetBinding(bindableProperty, bindingBase);
+		}
+
+		static BindableProperty CreateBindableProperty<TNativeView>(string targetProperty) where TNativeView : class
+		{
+			return BindableProperty.Create(
+					targetProperty,
+					typeof(object),
+					typeof(BindableObjectProxy<TNativeView>),
+					defaultBindingMode: BindingMode.Default,
+					propertyChanged: (bindable, oldValue, newValue) => {
+						TNativeView nativeView;
+						if ((bindable as BindableObjectProxy<TNativeView>).TargetReference.TryGetTarget(out nativeView))
+							SetNativeValue(nativeView, targetProperty, newValue);
+				}
+			);
+		}
+
+		static void SetNativeValue<TNativeView>(TNativeView target, string targetProperty, object newValue) where TNativeView : class
+		{
+			var mi = target.GetType().GetProperty(targetProperty)?.SetMethod;
+			if (mi == null)
+				throw new InvalidOperationException(Format("Native Binding on {0}.{1} failed due to missing or inaccessible property", target.GetType(), targetProperty));
+			mi.Invoke(target, new[] { newValue });
+		}
+
+		static void SetValueFromNative<TNativeView>(TNativeView target, string targetProperty, BindableProperty bindableProperty) where TNativeView : class
+		{
+			BindableObjectProxy<TNativeView> proxy;
+			if (!BindableObjectProxy<TNativeView>.BindableObjectProxies.TryGetValue(target, out proxy))
+				return;
+			SetValueFromRenderer(proxy, bindableProperty, target.GetType().GetProperty(targetProperty)?.GetMethod.Invoke(target, new object [] { }));
+		}
+
+		static void SetValueFromRenderer(BindableObject bindable, BindableProperty property, object value)
+		{
+			bindable.SetValueCore(property, value);
+		}
+
+		public static void SetBinding<TNativeView>(TNativeView target, BindableProperty targetProperty, BindingBase binding) where TNativeView : class
+		{
+			if (target == null)
+				throw new ArgumentNullException(nameof(target));
+			if (targetProperty == null)
+				throw new ArgumentNullException(nameof(targetProperty));
+			if (binding == null)
+				throw new ArgumentNullException(nameof(binding));
+			
+			var proxy = BindableObjectProxy<TNativeView>.BindableObjectProxies.GetValue(target, (TNativeView key) => new BindableObjectProxy<TNativeView>(key));
+			proxy.BindingsBackpack.Add(new KeyValuePair<BindableProperty, BindingBase>(targetProperty, binding));
+		}
+
+		public static void SetValue<TNativeView>(TNativeView target, BindableProperty targetProperty, object value) where TNativeView : class
+		{
+			if (target == null)
+				throw new ArgumentNullException(nameof(target));
+			if (targetProperty == null)
+				throw new ArgumentNullException(nameof(targetProperty));
+
+			var proxy = BindableObjectProxy<TNativeView>.BindableObjectProxies.GetValue(target, (TNativeView key) => new BindableObjectProxy<TNativeView>(key));
+			proxy.ValuesBackpack.Add(new KeyValuePair<BindableProperty, object>(targetProperty, value));
+		}
+
+		public static void SetBindingContext<TNativeView>(TNativeView target, object bindingContext, Func<TNativeView, IEnumerable<TNativeView>> getChild = null) where TNativeView : class
+		{
+			if (target == null)
+				throw new ArgumentNullException(nameof(target));
+
+			var proxy = BindableObjectProxy<TNativeView>.BindableObjectProxies.GetValue(target, (TNativeView key) => new BindableObjectProxy<TNativeView>(key));
+			proxy.BindingContext = bindingContext;
+			if (getChild == null)
+				return;
+			var children = getChild(target);
+			if (children == null)
+				return;
+			foreach (var child in children)
+				if (child != null)
+					SetBindingContext(child, bindingContext, getChild);
+		}
+
+		internal static void TransferBindablePropertiesToWrapper<TNativeView, TNativeWrapper>(TNativeView nativeView, TNativeWrapper wrapper)
+			where TNativeView : class
+			where TNativeWrapper : View
+		{
+			BindableObjectProxy<TNativeView> proxy;
+			if (!BindableObjectProxy<TNativeView>.BindableObjectProxies.TryGetValue(nativeView, out proxy))
+				return;
+			proxy.TransferAttachedPropertiesTo(wrapper);
+		}
+
+		class EventWrapper : INotifyPropertyChanged
+		{
+			string TargetProperty { get; set; }
+			static readonly MethodInfo s_handlerinfo = typeof(EventWrapper).GetRuntimeMethods().Single(mi => mi.Name == "OnPropertyChanged" && mi.IsPublic == false);
+
+			public EventWrapper(object target, string targetProperty, string updateSourceEventName)
+			{
+				TargetProperty = targetProperty;
+				Delegate handlerDelegate = null;
+				EventInfo updateSourceEvent=null;
+				try {
+					updateSourceEvent = target.GetType().GetRuntimeEvent(updateSourceEventName);
+					handlerDelegate = s_handlerinfo.CreateDelegate(updateSourceEvent.EventHandlerType, this);
+				} catch (Exception){
+					throw new ArgumentException(Format("No declared or accessible event {0} on {1}",updateSourceEventName,target.GetType()), nameof(updateSourceEventName));
+				}
+				if (updateSourceEvent != null && handlerDelegate != null)
+					updateSourceEvent.AddEventHandler(target, handlerDelegate);
+			}
+
+			[Preserve]
+			void OnPropertyChanged(object sender, EventArgs e)
+			{
+				PropertyChanged?.Invoke(sender, new PropertyChangedEventArgs(TargetProperty));
+			}
+
+			public event PropertyChangedEventHandler PropertyChanged;
+		}
+
+		//This needs to be internal for testing purposes
+		internal class BindableObjectProxy<TNativeView> : BindableObject where TNativeView : class
+		{
+			public static ConditionalWeakTable<TNativeView, BindableObjectProxy<TNativeView>> BindableObjectProxies { get; } = new ConditionalWeakTable<TNativeView, BindableObjectProxy<TNativeView>>();
+			public WeakReference<TNativeView> TargetReference { get; set; }
+			public IList<KeyValuePair<BindableProperty, BindingBase>> BindingsBackpack { get; } = new List<KeyValuePair<BindableProperty, BindingBase>>();
+			public IList<KeyValuePair<BindableProperty, object>> ValuesBackpack { get; } = new List<KeyValuePair<BindableProperty, object>>();
+
+			public BindableObjectProxy(TNativeView target)
+			{
+				TargetReference = new WeakReference<TNativeView>(target);
+			}
+
+			public void TransferAttachedPropertiesTo(View wrapper)
+			{
+				foreach (var kvp in BindingsBackpack)
+					wrapper.SetBinding(kvp.Key, kvp.Value);
+				foreach (var kvp in ValuesBackpack)
+					wrapper.SetValue(kvp.Key, kvp.Value);
+			}
+		}
+	}
+}
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj b/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
index 4fa202aa..9e961521 100644
--- a/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
+++ b/Xamarin.Forms.Core/Xamarin.Forms.Core.csproj
@@ -432,6 +432,7 @@
     <Compile Include="IAppIndexingProvider.cs" />
     <Compile Include="ListStringTypeConverter.cs" />
     <Compile Include="PoppedToRootEventArgs.cs" />
+    <Compile Include="NativeBindingHelpers.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
   <ItemGroup>