如何将下拉列表的值获取到MVC中的控制器

Question

i am trying to get the value of my dropdownlist to my controller with Jquery, everything i try , gives me a null pointer for the second parameter. Here is my code :

this is the jQuery code:

<script>
$(function () {

    $("#ddl").on("change", function () {
    var selectedID = $("#ddl").val();
    this.href = this.href.replace("idhotel", selectedID);
    });
});
</script>

this is my ActionLink:

   @Html.ActionLink("Voeg toe aan winkelwagentje", "Winkelwagen", new { id = Model.Id, hotelid="idhotel" }, new { @class = "btn btn-default" })

And this is my Action in the Controller: (just header)

public ActionResult Winkelwagen(int? id,int hotelid)
    {

        Console.Write("Please give me the hotelid: " + hotelid);
Return View();


}

and here is the dropdownlist:

 @Html.DropDownList("ddl", new SelectList(ViewBag.list, "Text", "Value"), "Select")

output dropdownlist:

error:

Server Error in '/' Application.

The parameters dictionary contains a null entry for parameter 'hotelid' of non- > nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult > Winkelwagen(System.Nullable`1[System.Int32], Int32)' > in 'TreinRittenVives.Controllers.ReizenController'. An optional parameter must > be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

Answer 1

Your second parameter is not nullable on the controller.

it should be...

public ActionResult Winkelwagen(int? id, int? hotelid)

If you want it to be a nullable type.

Regards

Craig

Answer 2

Try this:

 $("#ddl").on("change", function () {
    var selectedID = $("#ddl").val();
    $(a).prop("href", $(a).prop("href").replace("idhotel", selectedID));
    });

Answer 3

in your script this.href means your select element which ID is #ddl and select can't contain href attribute. so you can do something like

<script>
$(function () {
    $("#ddl").on("change", function () { 
    var newHref=$("a").attr("href").replace("idhotel", this.value);       
    $("a").attr("href",newHref);         
    });
});
</script>

Answer 4

Your Error:

Server Error in '/' Application. The parameters dictionary contains a null entry for parameter 'hotelid' of non- > nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult > Winkelwagen(System.Nullable`1[System.Int32], Int32)' > in 'TreinRittenVives.Controllers.ReizenController'. An optional parameter must > be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

Reason for error:

The above error will occur most of the time in development and the main reason for the above error, is when we write a action method in the controller , we will specify the parameters as non nullable that is without the question mark in the datatype ex.

Public void test(int a , int b)

The value must be passed, if we couldn't pass for some reason then the above error will occur.

Solution to Error: The best solution for the above problem is make the parameter as nullable

Nullable ex:

Public void test(int? a,int? b)

More info : https://docs.microsoft.com/en-us/dotnet/articles/csharp/programming-guide/nullable-types/