Using ChildActionOnly in MVC

Question

When would you use the attribute ChildActionOnly  What is a ChildAction and in what circumstance would you want restrict an action using this attribute

User · Answer

public class HomeController   Controller                   public ActionResult Index                             ViewBag TempValue    Index Action called at HomeController                 return View                            ChildActionOnly            public ActionResult ChildAction string param                            ViewBag Message    Child Action called      param                return View                            The code is initially invoking an Index action that in turn returns two Index views and at the View level it calls the ChildAction named    ChildAction                     ViewBag Title    Index                      lt h2 gt              Index          lt  h2 gt          lt  DOCTYPE html gt           lt html gt           lt head gt               lt title gt Error lt  title gt           lt  head gt           lt body gt               lt ul gt                 lt li gt                       ViewBag TempValue                  lt  li gt                   lt li gt  ViewBag OnExceptionError lt  li gt                     lt li gt   Html RenderAction  ChildAction   new   param    first       lt  li gt                       Html Action  ChildAction    Home   new   param    first                  lt  ul gt           lt  body gt           lt  html gt            Copy and paste the code to see the result  thanks

User · Answer

With   ChildActionOnly  attribute annotated  an action method can be called only as a child method from within a view  Here is an example  for   ChildActionOnly     there are two action methods  Index   and MyDateTime   and corresponding Views  Index cshtml and MyDateTime cshtml  this is HomeController cs  public class HomeController   Controller        public ActionResult Index                 ViewBag Message    This is from Index             var model   DateTime Now          return View model               ChildActionOnly      public PartialViewResult MyDateTime                 ViewBag Message    This is from MyDateTime              var model   DateTime Now          return PartialView model              Here is the view for Index cshtml    model DateTime        ViewBag Title    Index      lt h2 gt      Index lt  h2 gt   lt div gt      This is the index view for Home    Model ToLongTimeString    lt  div gt   lt div gt       Html Action  MyDateTime       Calling the partial view  MyDateTime     lt  div gt    lt div gt       ViewBag Message  lt  div gt    Here is MyDateTime cshtml partial view    model DateTime   lt p gt  This is the child action result   Model ToLongTimeString    lt br   gt   ViewBag Message  lt  p gt     if you run the application and do this request http   localhost 57803 home mydatetime  The result will be Server Error like so      This means you can not directly call the partial view  but it can be called via Index   view as in the Index cshtml       Html Action  MyDateTime       Calling the partial view  MyDateTime       If you remove  ChildActionOnly  and do the same request http   localhost 57803 home mydatetime it allows you to get the mydatetime partial view result    This is the child action result  12 53 31 PM  This is from MyDateTime

User · Answer

A little late to the party  but     The other answers do a good job of explaining what effect the  ChildActionOnly  attribute has  However  in most examples  I kept asking myself why I d create a new action method just to render a partial view  within another view  when you could simply render  Html Partial   MyParialView   directly in the view  It seemed like an unnecessary layer  However  as I investigated  I found that one benefit is that the child action can create a different model and pass that to the partial view  The model needed for the partial might not be available in the model of the view in which the partial view is being rendered  Instead of modifying the model structure to get the necessary objects properties there just to render the partial view  you can call the child action and have the action method take care of creating the model needed for the partial view   This can come in handy  for example  in  Layout cshtml  If you have a few properties common to all pages  one way to accomplish this is use a base view model and have all other view models inherit from it  Then  the  Layout can use the base view model and the common properties  The downside  which is subjective  is that all view models must inherit from the base view model to guarantee that those common properties are always available  The alternative is to render  Html Action in those common places  The action method would create a separate model needed for the partial view common to all pages  which would not impact the model for the  main  view  In this alternative  the  Layout page need not have a model  It follows that all other view models need not inherit from any base view model   I m sure there are other reasons to use the  ChildActionOnly  attribute  but this seems like a good one to me  so I thought I d share

User · Answer

The ChildActionOnly attribute ensures that an action method can be called only as a child method from within a view  An action method doesn   t need to have this attribute to be used as a child action  but we tend to use this attribute to prevent the action methods from being invoked as a result of a user request  Having defined an action method  we need to create what will be rendered when the action is invoked  Child actions are typically associated with partial views  although this is not compulsory     ChildActionOnly  allowing restricted access via code in View State Information implementation for specific page URL  Example  Payment Page URL  paying only once  razor syntax allows to call specific actions conditional

User · Answer

You would use it if you are using RenderAction in any of your views  usually to render a partial view   The reason for marking it with  ChildActionOnly  is that you need the controller method to be public so you can call it with RenderAction but you don t want someone to be able to navigate to a URL  e g   Controller SomeChildAction  and see the results of that action directly

User · Answer

FYI   ChildActionOnly  is not available in ASP NET MVC Core  see some info here

[c#] Using ChildActionOnly in MVC

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