Marqueone Marqueone - 1 month ago 24
ASP.NET (C#) Question

Unable to utilize UrlHelper

I'm currently trying to do something that was dead simple and straight forward in ASP.NET 4 however this ins't the case now in ASP.NET 5.

Previously to use the UrlHelper it was dead simple:

var urlHelper = new UrlHelper(HttpContext.Current.Request.RequestContext);


However I can't for the life of me wrap my head around how to use the new UrlHelper. I'm looking at the test cases and either I'm completely daft or I'm missing something and I can't seem to figure it out. Any help here in clearing up this would be great.

Answer

Update - Post RC2

As @deebo mentioned, you no longer can get an IUrlHelper directly from DI. Instead you need to inject an IUrlHelperFactory and an IActionContextAccessor into your class and use them to get the IUrlHelper instance as in:

public MyClass(IUrlHelperFactory urlHelperFactory, IActionContextAccessor actionAccessor)
{
    this.urlHelperFactory = urlHelperFactory;
    this.actionAccessor = actionAccessor;
}

public void SomeMethod()
{
    var urlHelper = this.urlHelperFactory.GetUrlHelper(this.actionAccessor.ActionContext);
}

You need to also register the in your startup class (IUrlHelperFactory is already registered by default):

services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

I have retrieved the IUrlHelper using the IServiceProvider in HttpContext.RequestServices.

Usually you will have an HttpContext property at hand:

  • In a controller action method you can do:

    var urlHelper = this.Context.RequestServices.GetRequiredService<IUrlHelper>();
    ViewBag.Url = urlHelper.Action("Contact", "Home", new { foo = 1 });
    
  • In a filter you can do:

    public void OnActionExecuted(ActionExecutedContext context)
    {
        var urlHelper = context.HttpContext.RequestServices.GetRequiredService<IUrlHelper>();
        var actionUrl = urlHelper.Action("Contact", "Home", new { foo = 1 });
        //use actionUrl ...
    }
    

Another option would be taking advantage of the built-in dependency injection, for example your controller could have a constructor like the following one and at runtime an IUrlHelper instance will be provided:

private IUrlHelper _urlHelper;
public HomeController(IUrlHelper urlHelper)
{
    _urlHelper = urlHelper;
}
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