SetterValueProvider.cs

using System.Collections.Generic;

using Mono.Cecil;
using Mono.Cecil.Cil;

using Xamarin.Forms.Xaml;
using Xamarin.Forms.Build.Tasks;
using System.Xml;

namespace Xamarin.Forms.Core.XamlC
{
	class SetterValueProvider : ICompiledValueProvider
	{
		public IEnumerable<Instruction> ProvideValue(VariableDefinitionReference vardefref, ModuleDefinition module, BaseNode node, ILContext context)
		{
			INode valueNode = null;
			if (!((IElementNode)node).Properties.TryGetValue(new XmlName("", "Value"), out valueNode) &&
			    !((IElementNode)node).Properties.TryGetValue(new XmlName(XamlParser.XFUri, "Value"), out valueNode) &&
				((IElementNode)node).CollectionItems.Count == 1)
				valueNode = ((IElementNode)node).CollectionItems[0];

			var bpNode = ((ValueNode)((IElementNode)node).Properties[new XmlName("", "Property")]);
			var bpRef = (new BindablePropertyConverter()).GetBindablePropertyFieldReference((string)bpNode.Value, module, bpNode);

			if (SetterValueIsCollection(bpRef, module, node, context))
				yield break;

			if (valueNode == null)
				throw new XamlParseException("Missing Value for Setter", (IXmlLineInfo)node);

			//if it's an elementNode, there's probably no need to convert it
			if (valueNode is IElementNode)
				yield break;

			var value = ((string)((ValueNode)valueNode).Value);
			var setterType = ("Xamarin.Forms.Core", "Xamarin.Forms", "Setter");

			//push the setter
			foreach (var instruction in vardefref.VariableDefinition.LoadAs(module.GetTypeDefinition(setterType), module))
				yield return instruction;

			//push the value
			foreach (var instruction in ((ValueNode)valueNode).PushConvertedValue(context, bpRef, valueNode.PushServiceProvider(context, bpRef: bpRef), boxValueTypes: true, unboxValueTypes: false))
				yield return instruction;

			//set the value
			yield return Instruction.Create(OpCodes.Callvirt, module.ImportPropertySetterReference(setterType, propertyName: "Value"));
		}

		static bool SetterValueIsCollection(FieldReference bindablePropertyReference, ModuleDefinition module, BaseNode node, ILContext context)
		{
			var items = (node as IElementNode)?.CollectionItems;

			if (items == null || items.Count <= 0)
				return false;

			// Is this a generic type ?
			var generic = bindablePropertyReference.GetBindablePropertyType(node, module) as GenericInstanceType;

			// With a single generic argument?
			if (generic?.GenericArguments.Count != 1)
				return false;

			// Is the generic argument assignable from this value?
			var genericType = generic.GenericArguments[0];

			if (!(items[0] is IElementNode firstItem))
				return false;

			return context.Variables[firstItem].VariableType.InheritsFromOrImplements(genericType);
		}
	}
}