Error implementing a Custom Model Binder in Asp.Net Web API

Question

im stuck with this very strange problem.
i have an API Controller named AttendanceController derived from APIControllerFA which is inturn derived from ApiController
here is the code

public class AttendanceController : ApiControllerFA
    {
        public HttpResponseMessage PostAttendance([ModelBinder(typeof(AttendanceRegistrationModelBinder))]AttendanceRegistrationModel model)
        {
            //checking model state for errors
            //throw new Exception("Just to throw an error ");

            ...........

As can be seen on the PostAttendance method i have a custom ModelBinder named AttendenceRegistrationModelBinder for which this is the code

public class AttendanceRegistrationModelBinder :  DefaultModelBinder
    {

        protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
        {
            if (propertyDescriptor.Name == "formJson")
            {
                string val = bindingContext.ValueProvider.GetValue(propertyDescriptor.Name).AttemptedValue;
                dynamic jsonVal = JsonConvert.DeserializeObject(val);
                propertyDescriptor.SetValue(bindingContext.Model, jsonVal);
                return;
                //SetProperty(controllerContext, bindingContext,propertyDescriptor,jsonVal);
            }
            base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
        }


    }

but when i try to access this controller using the Fiddler. i get an error saying

Could not create a 'IModelBinder' from 'AttendanceRegistrationModelBinder'. Please ensure it derives from 'IModelBinder' and has a public parameterless constructor

what am i doing wrong here?

Mark Jones · Accepted Answer · 2012-12-11 11:16:38Z

11

The issue you are having is that you are using the MVC model binder not the WebApi. It looks like you are deriving from System.Web.Mvc.DefaultModelBinder which implements System.Web.Mvc.IModelBinder.

To create a custom model binder for WebApi you need to implement System.Web.Http.IModelBinder.

Take a look at the model binders available in WebApi e.g. the CompsiteModelBinder http://aspnetwebstack.codeplex.com/SourceControl/changeset/view/f079d76e57b5#src%2fSystem.Web.Http%2fModelBinding%2fBinders%2fCompositeModelBinder.cs.

Some useful resources here and here.

Have you considered using a JToken for your Json form field this may work without a custom binder.

edited Dec 11, 2012 at 11:16

answered Dec 11, 2012 at 10:00

Mark Jones

12.2k2 gold badges52 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Error implementing a Custom Model Binder in Asp.Net Web API

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related