Nuclex.Support/Source/Plugins/FactoryEmployer.cs

117 lines
4.3 KiB
C#

#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2008 Nuclex Development Labs
This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.
You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion
using System;
using System.Collections.Generic;
namespace Nuclex.Support.Plugins {
/// <summary>Abstract factory</summary>
/// <typeparam name="T">Interface or base class of the product of the factory</typeparam>
public interface IFactory<T> {
/// <summary>The concrete type as implemented by the factory instance</summary>
Type ConcreteType { get; }
/// <summary>Creates a new instance of the type to which the factory is specialized</summary>
/// <returns>The newly created instance</returns>
T CreateInstance();
}
/// <summary>Employer to create factories of suiting types found in plugins</summary>
/// <typeparam name="T">Interface or base class that the types need to implement</typeparam>
/// <remarks>
/// <para>
/// This employer will not directly instanciate any compatible types found in
/// plugin assemblies, but generated runtime-factories of these types, enabling the
/// user to decide when and how many instances of a type will be created.
/// </para>
/// <para>
/// This approach has the advantage that it enables even assemblies that were not
/// intended to be plugins can be loaded as plugins, without risking an instanciation
/// or complex and possibly heavy-weight types. The disadvantage is that the
/// runtime-factory can not provide decent informationa about the plugin type like
/// a human-readable name, capabilities or an icon.
/// </para>
/// </remarks>
public class FactoryEmployer<T> : Employer {
#region class Factory
/// <summary>Concrete factory for the types in a plugin assembly</summary>
private class Factory : IFactory<T> {
/// <summary>Initializes a factory and configures it for the specified product</summary>
/// <param name="type">Type of which the factory creates instances</param>
public Factory(Type type) {
this.concreteType = type;
}
/// <summary>The concrete type as produced by the factory</summary>
public Type ConcreteType {
get { return this.concreteType; }
}
/// <summary>Create a new instance of the type that the factory is configured to</summary>
/// <returns>The newly created instance</returns>
public T CreateInstance() {
return (T)Activator.CreateInstance(this.concreteType);
}
/// <summary>Concrete product which the factory instance creates</summary>
private Type concreteType;
}
#endregion // class Factory
/// <summary>Initializes a new FactoryEmployer</summary>
public FactoryEmployer() {
this.employedFactories = new List<IFactory<T>>();
}
/// <summary>List of all factories that the instance employer has created</summary>
public List<IFactory<T>> Factories {
get { return this.employedFactories; }
}
/// <summary>Determines whether the type suites the employer's requirements</summary>
/// <param name="type">Type which will be assessed</param>
/// <returns>True if the type can be employed</returns>
public override bool CanEmploy(Type type) {
return
PluginHelper.HasDefaultConstructor(type) &&
typeof(T).IsAssignableFrom(type);
}
/// <summary>Employs the specified plugin type</summary>
/// <param name="type">Type to be employed</param>
public override void Employ(Type type) {
this.employedFactories.Add(new Factory(type));
}
/// <summary>All factories that the instance employer has created</summary>
private List<IFactory<T>> employedFactories;
}
} // namespace Nuclex.Support.Plugins