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2012-09-09T12:34:35.540
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Use the following code to create a delegate, which is late bound in the type parameter. See also <a href="http://msdn.microsoft.com/en-us/library/b8ytshk6.aspx" rel="nofollow">How to: Examine and Instantiate Generic Types with Reflection</a>. <pre><code>abstract class ActionHelper { protected abstract Delegate CreateActionImpl(); // A subclass with a static type parameter private class ActionHelper<T> : ActionHelper { protected override Delegate CreateActionImpl() { // create an Action<T> and downcast return new Action<T>(obj => Console.WriteLine("Called = " + (object)obj)); } } public static Delegate CreateAction(Type type) { // create the type-specific type of the helper var helperType = typeof(ActionHelper<>).MakeGenericType(type); // create an instance of the helper // and upcast to base class var helper = (ActionHelper)Activator.CreateInstance(helperType); // call base method return helper.CreateActionImpl(); } } // Usage // Note: The "var" is always "Delegate" var @delegate = ActionHelper.CreateAction(anyTypeAtRuntime); </code></pre> That said, I don't recommend using this method. Instead, use <pre><code>Action<object> action = obj => Console.WriteLine("Called = " + obj); </code></pre> It offers <ul> <li>The same functionality. Your original code <code>"Called = " + obj"</code> calls <code>.ToString()</code> on the parameter. So does the above.</li> <li>No performance difference. If the <code>obj</code> parameter is a value type, both variants perform a boxing operation. The boxing in the first is not obvious, but <code>"Called = " + obj"</code> boxes value types.</li> <li>Shorter and less error-prone.</li> </ul>
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1. POHow can I dynamically create an Action<T> at runtime?
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1. CO"No performance difference" To what? you haven't provided any code that actually dynamically creates a delegate. You conveniently provide an abstract class with an abstract method `CreateActionImpl` but don't provide an implementation--the only method that would actually dynamically create the action.
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2. CO@Peter I've explained the performance implications in the paragraph following the claim. Also, the OP wanted _just the type parameter_ of the delegate late bound. Which the code does without Reflection.Emit.
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