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68357
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2008-09-16T00:54:28.360
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2008-09-16T00:54:28.360
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So you need a thing that can create instances of an unknown type that implements an interface. You've got basically three options: a factory object, a Type object, or a delegate. Here's the givens: <pre><code>public interface IInterface { void DoSomething(); } public class Foo : IInterface { public void DoSomething() { /* whatever */ } } </code></pre> Using Type is pretty ugly, but makes sense in some scenarios: <pre><code>public IInterface CreateUsingType(Type thingThatCreates) { ConstructorInfo constructor = thingThatCreates.GetConstructor(Type.EmptyTypes); return (IInterface)constructor.Invoke(new object[0]); } public void Test() { IInterface thing = CreateUsingType(typeof(Foo)); } </code></pre> The biggest problem with it, is that at compile time, you have no guarantee that Foo actually has a default constructor. Also, reflection is a bit slow if this happens to be performance critical code. The most common solution is to use a factory: <pre><code>public interface IFactory { IInterface Create(); } public class Factory<T> where T : IInterface, new() { public IInterface Create() { return new T(); } } public IInterface CreateUsingFactory(IFactory factory) { return factory.Create(); } public void Test() { IInterface thing = CreateUsingFactory(new Factory<Foo>()); } </code></pre> In the above, IFactory is what really matters. Factory is just a convenience class for classes that do provide a default constructor. This is the simplest and often best solution. The third currently-uncommon-but-likely-to-become-more-common solution is using a delegate: <pre><code>public IInterface CreateUsingDelegate(Func<IInterface> createCallback) { return createCallback(); } public void Test() { IInterface thing = CreateUsingDelegate(() => new Foo()); } </code></pre> The advantage here is that the code is short and simple, can work with any method of construction, and (with closures) lets you easily pass along additional data needed to construct the objects.
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1. POHow can you require a constructor with no parameters for types implementing an interface?
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