Delegating Action Result, mvc, code comments suggest edit

In my last post, I walked through a simple example of an ActionResult that you can use to transmit a file to the user’s browser along with a download prompt.

The MVC framework will include several useful action results for common tasks. However, we might not cover all results you might want to return. In this post, I walk through a simple result that will cover all remaining cases. With the DelegatingResult, you simply pass it a delegate. This provides ultimate control. Let’s see it in action.

public ActionResult Hello() {
  return new DelegatingResult(context => {
    context.HttpContext.Response.AddHeader("something", "something");
    context.HttpContext.Response.Write("Hello World!");

Notice that we pass in a lambda to the constructor of the action result. This lambda is a delegate of type Action<ControllerContext>. By doing this, the lines of code within that block (Response.AddHeader and Response.Write) are deferred till later.

Here’s the code for this action result.

public class DelegatingResult : ActionResult {
  public Action<ControllerContext> Command {
    private set;
  public DelegatingResult(Action<ControllerContext> command) {
    this.Command = command;

  public override void ExecuteResult(ControllerContext context) {
    if (context == null) {
      throw new ArgumentNullException("context");

I updated the sample I wrote in my last post to include this demo. Download the source.

Technorati Tags: aspnetmvc,actionresult,lambda

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