How would I create a model binder to bind an int a

I'm creating a GET endpoint in my ASP.NET MVC web API project which is intended to take a an integer array in the URL like this:

api.mything.com/stuff/2,3,4,5

This URL is served by an action that takes an int[] parameter:

public string Get(int[] ids)

By default, the model binding doesn't work - ids is just null.

So I created a model binder which creates an int[] from a comma-delimited list. Easy.

But I can't get the model binder to trigger. I created a model binder provider like this:

public override IModelBinder GetBinder(HttpConfiguration configuration, Type modelType)
{
  if (modelType == typeof(int[]))
  {
    return new IntArrayModelBinder();
  }

  return null;
}

It's wired up so I can see it execute on startup but still my ids parameter remains stubbornly null.

What do I need to do?

Following is one way of achieving your scenario:

configuration.ParameterBindingRules.Insert(0, IntArrayParamBinding.GetCustomParameterBinding);
----------------------------------------------------------------------
public class IntArrayParamBinding : HttpParameterBinding
{
    private static Task completedTask = Task.FromResult(true);

    public IntArrayParamBinding(HttpParameterDescriptor desc)
        : base(desc)
    {
    }

    public override Task ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken)
    {
        HttpRouteData routeData = (HttpRouteData)actionContext.Request.GetRouteData();

        // note: here 'id' is the route variable name in my route template.
        int[] values = routeData.Values["id"].ToString().Split(new char[] { ',' }).Select(i => Convert.ToInt32(i)).ToArray();

        SetValue(actionContext, values);

        return completedTask;
    }

    public static HttpParameterBinding GetCustomParameterBinding(HttpParameterDescriptor descriptor)
    {
        if (descriptor.ParameterType == typeof(int[]))
        {
            return new IntArrayParamBinding(descriptor);
        }

        // any other types, let the default parameter binding handle
        return null;
    }

    public override bool WillReadBody
    {
        get
        {
            return false;
        }
    }
}