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copied!<p>Easy (and with three different GOF design patterns).</p> <p>Since we can't do anything with the components, we'll have to use the bridge pattern. </p> <p>Let's define handlers:</p> <pre><code>public interface IHandlerOf<T> where T : Component { void DoWork(T component); } </code></pre> <p>So now we can create a handler type for each component type that we want to handle. A DB component handler would look like this:</p> <pre><code>public class DbComponentHandler : IHandlerOf<DbComponent> { public void DoWork(DbComponent component) { // do db specific information here } } </code></pre> <p>But since we don't really want to keep track of all handlers we'll want to create a class that does it for us. We ultimately want to invoke the code just as in your example: </p> <pre><code>foreach (Component component in ComponentList) { handler.DoWork(component); } </code></pre> <p>But let's make it a bit cooler:</p> <pre><code>//maps handlers to components var service = new ComponentService(); // register all handlers in the current assembly service.Register(Assembly.GetExecutingAssembly()); // fake a component var dbComponent = new DbComponent(); // the cool part, the invoker doesn't have to know // about the handlers = facade pattern service.Invoke(dbComponent); </code></pre> <p>The service with makes it possible looks like this:</p> <pre><code>public class ComponentService { private readonly Dictionary<Type, IHandlerInvoker> _handlers = new Dictionary<Type, IHandlerInvoker>(); public void Register(Assembly assembly) { foreach (var type in assembly.GetTypes()) { if (type.IsInterface) continue; foreach (var interfaceType in type.GetInterfaces()) { if (!interfaceType.IsGenericType || interfaceType.GetGenericTypeDefinition() != typeof(IHandlerOf<>)) continue; var componentType = interfaceType.GetGenericArguments()[0]; var instance = Activator.CreateInstance(type); var method = instance.GetType().GetMethod("DoWork", new[] { componentType }); _handlers[componentType] = new ReflectionInvoker(instance, method); } } } public void Register<T>(IHandlerOf<T> handler) where T : Component { _handlers[typeof (T)] = new DirectInvoker<T>(handler); } #region Nested type: DirectInvoker private class DirectInvoker<T> : IHandlerInvoker where T : Component { private readonly IHandlerOf<T> _handler; public DirectInvoker(IHandlerOf<T> handler) { _handler = handler; } #region IHandlerInvoker Members public void Invoke(Component component) { _handler.DoWork((T) component); } #endregion } #endregion #region Nested type: IHandlerInvoker private interface IHandlerInvoker { void Invoke(Component component); } #endregion #region Nested type: ReflectionInvoker private class ReflectionInvoker : IHandlerInvoker { private readonly object _instance; private readonly MethodInfo _method; public ReflectionInvoker(object instance, MethodInfo method) { _instance = instance; _method = method; } #region IHandlerInvoker Members public void Invoke(Component component) { _method.Invoke(_instance, new object[] {component}); } #endregion } #endregion public void Invoke(Component component) { IHandlerInvoker invoker; if (!_handlers.TryGetValue(component.GetType(), out invoker)) throw new NotSupportedException("Failed to find a handler for " + component.GetType()); invoker.Invoke(component); } } </code></pre> <p>Do note that the interface (<code>IHandlerOf<T></code>) is generic which means that we can't store it directly in a Dictionary. Hence we use the Adapter pattern to store all handlers.</p> <hr> <p>Full example:</p> <pre><code>public interface IHandlerOf<in T> where T : Component { void DoWork(T component); } public class ComponentService { private readonly Dictionary<Type, IHandlerInvoker> _handlers = new Dictionary<Type, IHandlerInvoker>(); public void Register(Assembly assembly) { foreach (var type in assembly.GetTypes()) { if (type.IsInterface) continue; foreach (var interfaceType in type.GetInterfaces()) { if (!interfaceType.IsGenericType || interfaceType.GetGenericTypeDefinition() != typeof(IHandlerOf<>)) continue; var componentType = interfaceType.GetGenericArguments()[0]; var instance = Activator.CreateInstance(type); var method = instance.GetType().GetMethod("DoWork", new[] { componentType }); _handlers[componentType] = new ReflectionInvoker(instance, method); } } } public void Register<T>(IHandlerOf<T> handler) where T : Component { _handlers[typeof (T)] = new DirectInvoker<T>(handler); } #region Nested type: DirectInvoker private class DirectInvoker<T> : IHandlerInvoker where T : Component { private readonly IHandlerOf<T> _handler; public DirectInvoker(IHandlerOf<T> handler) { _handler = handler; } #region IHandlerInvoker Members public void Invoke(Component component) { _handler.DoWork((T) component); } #endregion } #endregion #region Nested type: IHandlerInvoker private interface IHandlerInvoker { void Invoke(Component component); } #endregion #region Nested type: ReflectionInvoker private class ReflectionInvoker : IHandlerInvoker { private readonly object _instance; private readonly MethodInfo _method; public ReflectionInvoker(object instance, MethodInfo method) { _instance = instance; _method = method; } #region IHandlerInvoker Members public void Invoke(Component component) { _method.Invoke(_instance, new object[] {component}); } #endregion } #endregion public void Invoke(Component component) { IHandlerInvoker invoker; if (!_handlers.TryGetValue(component.GetType(), out invoker)) throw new NotSupportedException("Failed to find a handler for " + component.GetType()); invoker.Invoke(component); } } public class DbComponent : Component { } public class DbComponentHandler : IHandlerOf<DbComponent> { public void DoWork(DbComponent component) { // do db specific information here Console.WriteLine("some work done!"); } } internal class Program { private static void Main(string[] args) { var service = new ComponentService(); service.Register(Assembly.GetExecutingAssembly()); var dbComponent = new DbComponent(); service.Invoke(dbComponent); } } </code></pre>

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