Siim Viikman's blog

In ASP.NET MVC, every controller method which is public and not marked with NonAction attribute is considered as an action. And action name is the same as method name. But you can also provide ActionName attribute with specified action name. There is also different attributes to constrain actions to handle only specified HTTP methods (GET, POST, PUT etc). All that information is used when finding which controller method to execute.

So, when technically (in a sense of C#) you can create many method overloads for a controller method, you end up with runtime exception when you don’t further restrain those actions. For example, consider following controller:

public class ProductController : Controller
{
	public ActionResult Edit(int id)
	{
		return View("Edit");
	}

	public ActionResult Edit(int id, ProductItem item)
	{
		return View("EditPost");
	}
}

public class ProductItem
{
	public int Id { get; set; }

	public string Name { get; set; }
}

When executing Edit action, MVC don’t know which method overload to execute, because current route could be handled by both of the Edit methods. But when decorating first method with HttpGet attribute and the second with HttpPost attribute, it works well.

Now, the trouble comes when you execute one of such methods from the view with RenderAtion method. Lets say you have two controllers:

public class ProductController : Controller
{
	public ActionResult Edit(int id)
	{
		return View("Edit");
	}

	[HttpPost]
	public ActionResult Edit(int id, ProductItem item)
	{
		return View("EditPost");
	}
}

public class ProductDetailController : Controller
{
	public ActionResult Edit(int id)
	{
		return View("EditDetail");
	}

	[HttpPost]
	public ActionResult Edit(int id, ProductDetailItem item)
	{
		return View("EditDetailPost");
	}
}

public class ProductDetailItem
{
	public string Type { get; set; }
}

public class ProductItem
{
	public int Id { get; set; }

	public string Name { get; set; }
}

ProductController is used to display product form view. On that form, I also call RenderAction to render Edit method on the ProductDetailController which displays some product sub-detail form. When executing first ProductController.Edit method, all works fine. When I submit product form, then the second Edit method is executed (because it handles POST requests).

At first, it looked like some weird behavior. But after when I gave a thought how MVC resolves which action method to execute, it all works out. It’s because RenderAction uses the same algorithm to resolve actions as a regular action link. So pay attention when using same pattern with controllers and actions.