This is what I used to be able to do:

string html = Html.RenderUserControl( "~/Views/Components/SomeControl.ascx", ViewData["SomeVDKey"], new {Width=200})%>

Nostalgia makes me weep.  For a short time, we Asp.Net developers had something so powerful, so flexible, so lovely, so easy to work into any scenario…  well, its gone now,  get on with it.

After much research, I eventually gave up on my desire to render user controls to a string.  The Mvc team is trying to provide a consistent design pattern and felt it was better to require you to execute actions when you want html output.  (Its the "we know best" attitude that gets me so fired up).  Along the same lines, properties on controls are no longer accessible because some view engines may not respect the object structure and extending the IView or IViewEngine interface would complicate things on that end.  Ok, I concede to your values and narcissistic tendencies.

Need begets innovation

Then I came across a place where I absolutely needed my html pre-rendered to a string.  My WebForm-based ascx would not accept the child content I was placing in it.  The behavior was that any script inside my tags would cause the outside control to fail render yet it rendered the child content - weird and completely unusable.  The original design used RenderUserControl to create the html and then set that as a string property in the container control.  No, not perfect.  But it worked!  It is WebForms smashing heads with MVC and the result is a blank page (and a blank stare).  I either had to completely reinvent the features or come up with some bridge to bring it back to life.

I really didn’t want to render an action from the view because I had all the data I needed already loaded in ViewData.  It hurts my sensibilities to load the whole stack and hit all the expensive resources a second time just for a small part of the page. 

Render Html from the Controller

Mike Hadlow had a better idea than all of us.  He realized that this need to render the output of an partial page and do something with it falls in the realm of business logic and probably belongs in the controller anyway.  He created an extension method for Controller that captures the output of an action as a string of html.  Now I can stick that in ViewData and pass it to the view as finished html.  Since I call this method after initializing ViewData, it does not require that I make an entire round trip or hit my database or other resources again.   Excellent.  Thank you so much!

What I have now:

string html = this.CaptureActionHtml<ResearchController>(c => (ViewResult)c.RatingsReturnChart() );

I’m using the extension posted here: http://mikehadlow.blogspot.com/2008/06/mvc-framework-capturing-output-of-view_05.html

That’s not bad.  Not bad at all.  Now I can pass that html to my view in the ViewData and modify my view to pull it from there rather than render itself.  I can deal.  Thanks for the save, Mike

This entry was posted on Wednesday, November 12th, 2008 at 7:56 am and is filed under Asp.Net, Mvc. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.