Why are Redirect Results not allowed in Child Actions in Asp.net MVC 2

Question

I have some partial actions that I render with the Asp.Net Futures RenderAction method. Some of these perform redirects after the forms in them have been processed.

Now that I upgraded to Asp.Net MVC 2 RC it gives me an error "Child actions are not allowed to perform redirect actions".

I checked out the source code and I found the line that throws the exception. To Get around it I can make a custom RedirectResult, But before I do I want to understand why the framework doesn't allow it in the first place. There must be a good reason and maybe I Shouldn't do either.

Any one know the reason for this limitation?

Thanks

Answer 1

The limitation exists because MVC has already started rendering a view to the client. The effect of redirecting from this point is undefined. It could work perfectly, it could continue rendering the original view without redirecting, it could throw a different exception, etc.

Since the result of performing this action is undefined, the framework blocks it. In practice, RenderAction should never be used to render anything other than a view (or view-like content) for similar reasons.

In your particular case, the outer action should redirect. If you're just going to end up redirecting from within the view anyway without showing anything to the user, then there was really no purpose to going through the view in the first place, as the outer action could have delegated the work appropriately on its own.