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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011 CPOL
This article will present two alternatives to Lazy.
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Properties
Settings.settings
Pfz
Caching
Collections
DataTypes
DynamicObjects
Internal
Extensions
Factoring
Pfz.csproj.user
Pfz.Phone.csproj.user
Pfz.ruleset
Pfz.Silverlight.csproj.user
Pfz.snk
Pfz.suo
PhoneSpecific
Properties
Remoting
Instructions
Internal
Serializers
Udp
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Disposers
Unsafe
using System;
using System.Reflection;
using Pfz.Extensions;
using System.Collections.Generic;
using System.Diagnostics;

namespace Pfz.Factoring
{
	/// <summary>
	/// Class that deals with the creation of the appropriate factory for the given factoryResultType (or base factory type).
	/// </summary>
	public static class Factories
	{
		/// <summary>
		/// Creates a new factory prepared to create instances of the given factoryResultType.
		/// </summary>
		public static IFactories Get(Type factoryResultType)
		{
			if (factoryResultType == null)
				throw new ArgumentNullException("factoryResultType");

			Type type = typeof(Factories<>).MakeGenericType(factoryResultType);
			var field = type.GetField("Instance");
			object result = field.GetValue(null);
			return (IFactories)result;
		}
	}

	/// <summary>
	/// Class that manages the factories. In it, you can register the types that will be returned for given data-types, or create specialized 
	/// factories for datat-types.
	/// </summary>
	/// <typeparam name="T">The type of the objects that will be created by this factory.</typeparam>
	public static class Factories<T>
	{
		#region Instance
			/// <summary>
			/// Gets an Instance for this Factory. Useful only if you want to use this by interfaces.
			/// </summary>
			public static IFactories<T> Instance = new FactoryInstance();

			private sealed class FactoryInstance:
				IFactories<T>
			{
				public IFactory<T> TryCreateFactory(Type dataType)
				{
					return Factories<T>.TryCreateFactory(dataType);
				}

				public IFactory<T> CreateFactory(Type dataType)
				{
					return Factories<T>.CreateFactory(dataType);
				}

				public IFactory<T> TryCreateFactory<DataType>()
				{
					return Factories<T>.TryCreateFactory<DataType>();
				}

				public IFactory<T> CreateFactory<DataType>()
				{
					return Factories<T>.CreateFactory<DataType>();
				}

				IFactory IFactories.TryCreateFactory(Type dataType)
				{
					return Factories<T>.TryCreateFactory(dataType);
				}

				IFactory IFactories.CreateFactory(Type dataType)
				{
					return Factories<T>.CreateFactory(dataType);
				}

				IFactory IFactories.TryCreateFactory<DataType>()
				{
					return Factories<T>.TryCreateFactory<DataType>();
				}

				IFactory IFactories.CreateFactory<DataType>()
				{
					return Factories<T>.CreateFactory<DataType>();
				}
			}
		#endregion

		private static TypeDictionary<KeyValuePair<Type, ConstructorInfo>> _dictionary = new TypeDictionary<KeyValuePair<Type, ConstructorInfo>>();
		static Factories()
		{
			if (!typeof(T).ContainsCustomAttribute<FactoryBaseAttribute>())
				throw new ArgumentException("Factories<T> can only accept [FactoryBase] interfaces as generic argument.", typeof(T).FullName);

			#if WINDOWS_PHONE
			#else
			var entryAssembly = Assembly.GetEntryAssembly();
			if (entryAssembly != null)
			{
				var referencedAssemblies = entryAssembly.GetReferencedAssemblies();
				foreach(var referencedAssembly in referencedAssemblies)
					Assembly.Load(referencedAssembly);
			}
			#endif

			foreach(var assembly in AppDomain.CurrentDomain.GetAssemblies())
			{
				foreach(var type in assembly.GetTypes())
				{
					var attributes = type.GetCustomAttributes<AutoRegisterInFactoryAttributeBase>();
					foreach(var attribute in attributes)
						if (attribute.BaseFactoryType == typeof(T))
							Register(type, attribute.DataType, attribute.CanBeUsedForSubDataTypes);
				}
			}
		}


		/// <summary>
		/// Registers a type to be created for the given datatype.
		/// </summary>
		public static void Register(Type typeToCreate, Type dataType, bool canCreateForSubDataTypes=false)
		{
			if (typeToCreate == null)
				throw new ArgumentNullException("typeToCreate");

			if (dataType == null)
				throw new ArgumentNullException("dataType");

			if (!typeof(T).IsAssignableFrom(typeToCreate))
				throw new ArgumentException(typeToCreate.FullName + " must implement " + typeof(T).FullName + ".", "typeToCreate");

			var constructor = typeToCreate.GetConstructor(Type.EmptyTypes);
			if (constructor == null)
				throw new ArgumentException(typeToCreate.FullName + " does not have a public default constructor.");

			var pair = new KeyValuePair<Type, ConstructorInfo>(dataType, constructor);
			_dictionary.Set(dataType, pair, canCreateForSubDataTypes);
		}

		/// <summary>
		/// Tries to register a factory for the given dataType.
		/// This will not unregister editors for parent dataTypes capable of editing sub-types.
		/// </summary>
		public static bool Unregister(Type dataType)
		{
			return _dictionary.Remove(dataType);
		}

		/// <summary>
		/// Gets a value indicating if a factory for the given dataType can be created.
		/// </summary>
		public static bool CanCreate(Type dataType)
		{
			var constructorPair = _dictionary.FindUpOrDefault(dataType);
			return constructorPair.Value != null;
		}

		/// <summary>
		/// Tries to create a factory for the given dataType.
		/// </summary>
		public static Factory<T, DataType> TryCreateFactory<DataType>()
		{
			var constructorPair = _dictionary.FindUpOrDefault(typeof(DataType));
			var constructor = constructorPair.Value;
			if (constructor == null)
				return null;

			var realType = constructor.DeclaringType;
			if (realType.ContainsGenericParameters)
				constructor = realType.MakeGenericType(typeof(DataType)).GetConstructor(Type.EmptyTypes);

			return new Factory<T, DataType>(constructor, constructorPair.Key);
		}

		private static readonly MethodInfo _method = ReflectionHelper.GetMethod(() => TryCreateFactory<int>()).GetGenericMethodDefinition();
		/// <summary>
		/// Tries to create a factory for the given dataType.
		/// </summary>
		public static IFactory<T> TryCreateFactory(Type dataType)
		{
			if (dataType == null)
				throw new ArgumentNullException("dataType");

			var method = _method.MakeGenericMethod(dataType);
			object result = method.Invoke(null, null);
			return (IFactory<T>)result;
		}

		/// <summary>
		/// Create a factory for the given dataType or throws an exception.
		/// </summary>
		public static Factory<T, DataType> CreateFactory<DataType>()
		{
			var result = TryCreateFactory<DataType>();

			if (result == null)
				throw new ArgumentException("Can't find a factory for the given data-type.");

			return result;
		}

		/// <summary>
		/// Create a factory for the given dataType or throws an exception.
		/// </summary>
		public static IFactory<T> CreateFactory(Type dataType)
		{
			var result = TryCreateFactory(dataType);

			if (result == null)
				throw new ArgumentException("Can't find a factory for the given data-type.");

			return result;
		}
	}
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Paulo Zemek
Engineer Microsoft Corporation
United States United States
I started to program computers when I was 11 years old, as a hobbist, programming in AMOS Basic and Blitz Basic for Amiga.
At 12 I had my first try with assembler, but it was too difficult at the time. Then, in the same year, I learned C and, after learning C, I was finally able to learn assembler (for Motorola 680x0).
Not sure, but probably between 12 and 13, I started to learn C++. I always programmed "in an object oriented way", but using function pointers instead of virtual methods.
 
At 15 I started to learn Pascal at school and to use Delphi. At 16 I started my first internship (using Delphi). At 18 I started to work professionally using C++ and since then I've developed my programming skills as a professional developer in C++ and C#, generally creating libraries that help other developers do they work easier, faster and with less errors.
 
Now I just started working as a Senior Software Engineer at Microsoft.
 
Want more info or simply want to contact me?
Take a look at: http://paulozemek.azurewebsites.net/
Or e-mail me at: paulozemek@outlook.com
 
Codeproject MVP 2012
Microsoft MVP 2013-2014

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