ASP NET MVC - passing parameters to the controller

Question

I have a controller with an action method as follows   public class InventoryController   Controller       public ActionResult ViewStockNext int firstItem                   Do some stuff           And when I run it I get an error stating      The parameters dictionary does not contain a valid value of type  System Int32  for parameter  firstItem   To make a parameter optional its type should either be a reference type or a Nullable type    I had it working at one point and I decided to try the function without parameters   Finding out that the controller was not persistant I put the parameter back in  now it refuses to recognise the parameter when I call the method   I m using this url syntax to call the action   http   localhost 2316 Inventory ViewStockNext 11   Any ideas why I would get this error and what I need to do to fix it    I ve tried adding another method that takes an integer to the class it it also fails with the same reason   I ve tried adding one that takes a string  and the string is set to null   I ve tried adding one without parameters and that works fine  but of course it won t suit my needs

User · Answer

There is another way to accomplish that (described in more details in Stephen Walther's Pager example

Essentially, you create a link in the view:

Html.ActionLink("Next page", "Index", routeData)

In routeData you can specify name/value pairs (e.g., routeData["page"] = 5), and in the controller Index function corresponding parameters receive the value. That is,

public ViewResult Index(int? page)

will have page passed as 5. I have to admit, it's quite unusual that string ("page") automagically becomes a variable - but that's how MVC works in other languages as well...

User · Answer

Using the ASP NET Core Tag Helper feature    lt a asp-controller  Home  asp-action  SetLanguage  asp-route-yourparam1   item Value  gt  item Text lt  a gt

User · Answer

To rephrase Jarret Meyer s answer  you need to change the parameter name to  id  or add a route like this  routes MapRoute           quot ViewStockNext quot      Route name          quot Inventory ViewStockNext  firstItem  quot       URL with parameters         new   controller    quot Inventory quot   action    quot ViewStockNext quot        Parameter defaults         The reason is the default route only looks for actions with no parameter or a parameter called  id   Edit  Heh  nevermind Jarret added a route example after posting

User · Answer

Or  you could try changing the parameter type to string  then convert the string to an integer in the method  I am new to MVC  but I believe you need nullable objects in your parameter list  how else will the controller indicate that no such parameter was provided  So     public ActionResult ViewNextItem string id

User · Answer

Your routing needs to be set up along the lines of  controller   action   firstItem   If you left the routing as the default  controller   action   id  in your global asax cs file  then you will need to pass in id   routes MapRoute       Inventory        Inventory  action   firstItem        new   controller    Inventory   action    ListAll   firstItem                 or something close to that

User · Answer

Or  you could try changing the parameter type to string  then convert the string to an integer in the method  I am new to MVC  but I believe you need nullable objects in your parameter list  how else will the controller indicate that no such parameter was provided  So     public ActionResult ViewNextItem string id

User · Answer

The reason for the special treatment of  id  is that it is added to the default route mapping  To change this  go to Global asax cs  and you will find the following line   routes MapRoute   Default     controller   action   id                      new   controller    Home   action    Index   id            Change it to   routes MapRoute   Default     controller   action                      new   controller    Home   action    Index

User · Answer

public ActionResult ViewNextItem int  id  makes the id integer a nullable type  no need for string lt - int conversions

User · Answer

or do it with Route Attribute   public class InventoryController   Controller        Route  whatever  firstItem         public ActionResult ViewStockNext int firstItem                int yourNewVariable   firstItem

User · Answer

Headspring created a nice library that allows you to add aliases to your parameters in attributes on the action   This looks like this    ParameterAlias  firstItem    id   Order   3   public ActionResult ViewStockNext int firstItem           Do some stuff     With this you don t have to alter your routing just to handle a different parameter name   The library also supports applying it multiple times so you can map several parameter spellings  handy when refactoring without breaking your public interface     You can get it from Nuget and read Jeffrey Palermo s article on it here

User · Answer

you can change firstItem to id and it will work  you can change the routing on global asax  i do not recommed that   and  can t believe no one mentioned this  you can call    http   localhost 2316 Inventory ViewStockNext firstItem 11   In a  Url Action would be     Url Action  ViewStockNext    Inventory   new  firstItem 11      depending on the type of what you are doing  the last will be more suitable  Also you should consider not doing ViewStockNext action and instead a ViewStock action with index   my 2cents

User · Answer

public ActionResult ViewNextItem int  id  makes the id integer a nullable type  no need for string lt - int conversions

[c#] ASP.NET MVC - passing parameters to the controller

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