RenderAction RenderPartial

From what I have understood there is a big difference between the Html.RenderPartial included in the ASP.NET MVC release and the HTML.RenderAction in the Microsoft.Web.Mvc.ViewExtensions included in MVC Futures.

On my application I have many pages composed from many "widgets" (sort of) each having its own specific function.

It seemed to me more reasonable to use the RenderAction method as each widget would have a dedicated controller responsible for getting different data and rendering a dedicated view (as opposed to having only one controller and a unique view model to pass to RenderPartial helper to render views).

From the tests I have done having a form that points to a Create action method in a controller like:

 <% using (Html.BeginForm("Create", "Message", FormMethod.Post, 
     new { id = "messageCreateForm" })) {%>

and calling it with

 <% Html.RenderPartial("MessageForm",new MessageDTO()); %>

will render correcly a:

<form id="messageCreateForm" method="post" action="/Message/Create">

but with the same equivalent with RenderAction (so using a MessageForm action method on the controller to render the view) would not render correcly so:

 <% Html.RenderAction<MessageController>(m => m.MessageForm()); %>

will render in:

<form id="messageCreateForm" method="post" action="">

Note that the action is empty.

Is this the correct way to use the RenderAction helper and is it correct to use it in cases like that?

UPDATE: Actually renaming the partial view to _MessageForm renders the form correcly.

Very old one, but it jumped into my list of unanswered questions :)

There is a big difference between RenderAction and RenderPartial. RenderPartial will render a View on the same controller (or a shared one), while RenderAction will actually perform an entire cycle of MVC, that is: it will instantiate the controller (any controller you mention, not just the current one), it will execute the action, and it will then return and render the result.

The RenderPartial is more similar to an inclusion, it will even share the same model if you don't specify a different one.

The RenderAction is much more complex (and there may be undesired side effects, that's why they did not make this function available since version 1 -- initially it was available as an experimental feature).

So in your case, if you have widgets, it's OK to use both. It depends on the complexity of the widget. If you have one that has to get data from a DB, do something complex, etc... then you should probably use RenderAction.

I have a News controller responsible for news objects. I created a Block action, which will render a block with the latest news to be put in the home page. This is a perfect example, in my opinion, for RenderAction.

Working with MVC requires much attention to not to shoot yourself in the foot. I mean it by the efficiency of the MVC products. In complex projects I would prefer to use RenderPartial rather than RenderAction. I use RenderPartial in which I use jQuery.ajax request (with Html.Action). It definitely works more efficiently than RenderAction. By this way you can put your Views into cache and then call jQuery.ajax. Try it yourselves. Ayende explains it clearly in Hibernating Rhinos.