ASP.NET MVC

ASP.NET MVC: Pass parameters when redirecting from one action to another

In ASP.NET MVC, it’s common to have a situation where you post to one controller action and then redirect to another controller action. Let’s say that you want to pass values from the first controller method to the other. The problem is that in out-of-the-box ASP.NET MVC, there is no way to redirect to another action and pass a parameter into the action that you are redirecting to. Here is one way you can get around this problem:

public class AccountController : Controller
{
    [AcceptGet]
    public ActionResult Index(IndexViewModel model)
    {
        model.Message = (string) TempData["Message"];

        return View(model);
    }

    [AcceptPost]
    public ActionResult Save(SaveUpdateModel model)
    {
        // save the information
        TempData["Message"] = model.Message;
        return RedirectToAction("Index");
    }
}

The reason that you would do a redirect in this case is so that (a) you can reuse the code in the Index method and (b) you are redirecting to a GET operation, so if the user clicks Refresh in their browser, it won’t try to re-post the previous page.

I don’t really like how that code works, for various reasons:

  • I’m using hardcoded strings (“Index” and “Message”). These might not get caught by refactoring tools if I want to change names, and I don’t get compile time checking on them.
  • In the Index() method, I have to grab the value out of TempData. That works fine if you’re being redirected from the Save() action, but what if I’m being redirected from another action? What if I’m not being redirected from anywhere and the user is accessing the action directly? Ideally, when the Index() method is called, it should have everything that it needs in its parameters at the beginning of the method.

Personally, I don’t like to see TempData or ViewData anywhere in my controller methods. Don’t get me wrong, I need them and I’m going to use them, but I want it all done under the covers. I favor the “One Model In, One Model Out” pattern, where each controller action method takes in one model parameter (or none) and returns another model. Doing it this way allows me to avoid the use of magic strings and hashtables. I want my code to look like this:

[PassParametersDuringRedirect]
public class AccountController : Controller
{
    [AcceptGet]
    public ActionResult Index(IndexPresentationModel model)
    {
        return View(model);
    }

    [AcceptPost]
    public ActionResult Save(SaveUpdateModel model)
    {
        // save the information

        var presentationModel = new IndexPresentationModel();

        presentationModel.Message = model.Message;

        return this.RedirectToAction(c => c.Index(presentationModel));
    }
}

This code does exactly what I want. Now…

  • I don’t have any magic strings.
  • Everything is strongly typed.
  • The parameter passed to the Index() method will always be complete. I don’t have to load anything out of TempData to get it to work.

One thing I love about ASP.NET MVC is that it is very extensible, so you can usually make it do what you want. This is the purpose of the MVCContrib project — people extending ASP.NET MVC to make it even better.

You may notice that in the code snippet above, I decorated my controller class with the [PassParametersDuringRedirect] attribute. Now, any parameters that I pass into RedirectToAction() will get passed into the action that I redirected to.

One slight problem… this new version of RedirectToAction() is an extension method on the Controller class, which means to call it, you would have to write “this.RedirectToAction()”. If you don’t want to have to write “this.” every time, you can just create a base controller class that has this method:

protected RedirectToRouteResult RedirectToAction(Expression> action) 
    where T : Controller
{
    return ControllerExtensions.RedirectToAction(this, action);
}
April 6, 2009by Jon Kruger