crashing when building link using UrlHelper and new uri .net core

Question

I am trying to create a link for pagination using IUrlhelper in .net core in my webapi.

I get the error

"Value cannot be null.Parameter name: uriString"

I have the following code in my start up:

    services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();
        services.AddScoped<IUrlHelper>(factory =>
        {
            var actionContext = factory.GetService<IActionContextAccessor>()
                                       .ActionContext;
            return new UrlHelper(actionContext);
        });

then I have a class that I build my paging links

public class LinkBuilder
{
    public LinkBuilder(IUrlHelper urlHelper,string routeName, PagingInfo pagingInfo)
    {

        var mylink = CreateLink(urlHelper, "GetMovies", pagingInfo.PageNumber, pagingInfo.PageSize);

        etc.....
    }

    private Uri CreateLink(IUrlHelper urlHelper,
                            string routeName,
                            int pageNo,
                            int pageSize)
    {
        //CRASHES ON NEW URI!  "Value cannot be null.
                                Parameter name: uriString"

        return new Uri(
        urlHelper.Link(routeName, 
        new { PageNumber = pageNo, PageSize = pageSize }));
    }

also if do the following my link is always null .Dont get it!!

//note urlhelper is not null when injected

        var link = urlHelper.Link("getsomething", new { PageNumber = 1, PageSize = 20});

    Any ideas what I am doing wrong?

    thanks

Answer 1

found my own answer. the name of the of the route must match the routename when i build the link.