Question

Currently I’m using a base class for some Customer model classes. As defined as follows

public abstract class BaseCustomerModel<T>
   where T : IUserEntity

For further clarification, the IUserEntity contains:

public interface IUserEntity
{
   string ErrorMessage { get; }
}

That property among some other things will be exposed in an ErrorTextControl.ascx:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<(...).Models.BaseCustomerModel<(...).IUserEntity>>" %>

<tr>
   <td colspan="2"><%: Html.DisplayFor(model => model.ErrorMessage) %></td>
</tr>

I’ll call the user control like so:

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage<(...).Models.MyUserModel>" %>
<% if (Model.HasErrors)
   {
      Html.RenderPartial("ErrorTextControl", Model);
   } %>

Last piece of code (MyUserEntity implements IUserEntity):

public class MyUserModel : BaseCustomerModel<MyUserEntity>

Unfortunately this obviously doesn’t work, because the generic type can’t be implicitly casted to an IUserEntity. Therefore resulting in the following error message in the browser:

Exception Details: System.InvalidOperationException: The model item passed into the dictionary is of type
‘(…).Models.MyUserModel’, but this dictionary requires a model item of type
‘(…).Models.BaseCustomerModel`1[(…).IUserEntity]’.

So questions:

• Is there any way to define a user control with a generic base class from which the type is not yet known? If yes, how to accomplish such thing?
• If not, any workaround, common solution or ideas to be able to have a generic user control?

Many thanks.

Answer 1

Well, just came up with a solution myself.

Just an extra interface to BaseCustomerModel:

public abstract class BaseCustomerModel<T> : IContainErrorMessage
   where T : IUserEntity

That way the user control doesn’t have to worry about the generics:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<(...).Models.IContainErrorMessage>" %>