Style.cs

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Reflection;
using System.Runtime.CompilerServices;
using Xamarin.Forms.Xaml;

namespace Xamarin.Forms.StyleSheets
{
	sealed class Style
	{
		Style()
		{
		}

		public IDictionary<string, string> Declarations { get; set; } = new Dictionary<string, string>();
		Dictionary<KeyValuePair<string, string>, object> convertedValues = new Dictionary<KeyValuePair<string, string>, object>();

		public static Style Parse(CssReader reader, char stopChar = '\0')
		{
			Style style = new Style();
			string propertyName = null, propertyValue = null;

			int p;
			reader.SkipWhiteSpaces();
			bool readingName = true;
			while ((p = reader.Peek()) > 0) {
				switch (unchecked((char)p)) {
				case ':':
					reader.Read();
					readingName = false;
					reader.SkipWhiteSpaces();
					break;
				case ';':
					reader.Read();
					if (!string.IsNullOrEmpty(propertyName) && !string.IsNullOrEmpty(propertyValue))
						style.Declarations.Add(propertyName, propertyValue);
					propertyName = propertyValue = null;
					readingName = true;
					reader.SkipWhiteSpaces();
					break;
				default:
					if ((char)p == stopChar)
						return style;

					if (readingName) {
						propertyName = reader.ReadIdent();
						if (propertyName == null)
							throw new Exception();
					} else 
						propertyValue = reader.ReadUntil(stopChar, ';', ':');
					break;
				}
			}
			return style;
		}

		public void Apply(VisualElement styleable)
		{
			if (styleable == null)
				throw new ArgumentNullException(nameof(styleable));

			foreach (var decl in Declarations) {
				var property = ((IStylable)styleable).GetProperty(decl.Key);
				if (property == null)
					continue;
				if (string.Equals(decl.Value, "none", StringComparison.OrdinalIgnoreCase))
					styleable.ClearValue(property, fromStyle: true);
				else {
					object value;
					if (!convertedValues.TryGetValue(decl, out value))
						convertedValues[decl] = (value = Convert(styleable, decl.Value, property));
					styleable.SetValue(property, value, fromStyle: true);
				}
			}

			foreach (var child in styleable.LogicalChildrenInternal) {
				var ve = child as VisualElement;
				if (ve == null)
					continue;
				Apply(ve);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		static object Convert(object target, object value, BindableProperty property)
		{
			Func<MemberInfo> minforetriever = () =>    property.DeclaringType.GetRuntimeProperty(property.PropertyName) as MemberInfo
													?? property.DeclaringType.GetRuntimeMethod("Get" + property.PropertyName, new[] { typeof(BindableObject) }) as MemberInfo;
			var serviceProvider = new StyleSheetServiceProvider(target, property);
			return value.ConvertTo(property.ReturnType, minforetriever, serviceProvider);
		}

		public void UnApply(IStylable styleable)
		{
			throw new NotImplementedException();
		}
	}
}