Related
I setup a route like that:
routes.MapRoute(
name: "Pesquisar",
url: "Pesquisar/{aaa}/{bbb}/{id}",
defaults: new { controller = "Home", action = "Pesquisar",
aaa = UrlParameter.Optional,
bbb = UrlParameter.Optional,
id = UrlParameter.Optional
}
);
When I press Send button in a form (with GET method) the url is like that:
http://localhost:00000/Pesquisar?aaa=One&bbb=Two
But I was expecting for:
http://localhost:00000/Pesquisar/One/Two
When you map a rout, it adds it to the end of a list. When the router looks for the rule to match, it starts at the begining of the list and itterates through it. It will take the first rule that matches, not the most specific rule. Because it is natural to append code to the end, the default rule (which works for almost everything) will be at the start.
Try re-ordering your code to look like this:
///The specific rout which you want to use
routes.MapRoute(
name: "Pesquisar",
url: "{action}/{aaa}/{bbb}/{id}",
defaults: new { controller = "Home", action = "Pesquisar",
aaa = UrlParameter.Optional,
bbb = UrlParameter.Optional,
id = UrlParameter.Optional
}
);
///The generic catch all router
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
More information can be found in this question:
Setting up ASP.Net MVC 4 Routing with custom segment variables
When I press Send button in a form (with GET method) the url is like that:
http://mydomain.com/Pesquisar?aaa=One&bbb=Two
But I was expecting for:
http://mydomain.com/One/Two
This is because the browser is unaware of the fancy url you want, as the standard form Get method is to append form values in the querystring.
What you mostly likely have to do is something like Creating Canonical URLs including an id and title slug, except redirect to the url you want if it's not the url you want to display.
Or you can use jQuery to manually create the url you want on submit, but requires more client side work.
Not sure if you get a clean URL directly from a html form GET.
One suggestion would be to POST it to an action, do what you need to do with the data, then on completion, redirect to your clean URL.
e.g.
ViewModel:
public sealed class PesquisarModel
{
public string aaa { get; set; }
public string bbb { get; set; }
public string id { get; set; }
}
Controller Actions:
[HttpGet]
public ActionResult Pesquisar(PesquisarModel m)
{
return View();
}
[HttpPost]
[ActionName("Pesquisar")]
public ActionResult PesquisarPost(PesquisarModel m)
{
//do stuff
return RedirectPermanent("/pesquisar/" + m.aaa + "/" + m.bbb + "/" + m.id);
}
View:
#model MyApplication.Models.PesquisarModel
#using (Html.BeginForm())
{
#Html.TextBoxFor(m => m.aaa)
#Html.TextBoxFor(m => m.bbb)
#Html.TextBoxFor(m => m.id)
<button type="submit">Submit</button>
}
This is the browser behavior. When making a GET request browser appends all KeyValue pairs to querystring.
The mentioned route format will be available, when we use Html.ActionLink or Html.RouteUrl etc.
You could probably write few code in OnActionExecuting ( or you can use any handler) to reconstruct RouteData and redirect with appropriate url. Below code is not tested
var queries = this.Request.QueryString;
foreach(var query in queries)
{
// Add/Update to RequestContext.RouteData
}
var redirectUrl = Url.RouteUrl("Pesquisar",this.RequestContext.RouteData);
Response.Redirect(redirectUrl);
That's expected behavior.
The routing system is on server side. The browser knows nothing about routes, and what you're doing happens in the browser.
If you want to get that route you have to compose it on the client side with a custom script which uses the <form>'s action, an the values of the <input type="text"> values.
You cannot generate the Url on the server side (which could be done with some UrlHelper extension methods) because the changes on the text boxes wouldn't be updated.
This is not advisable because if you make changes on the routes, you could forget to update them in your browser scripts, breaking you application.
You could avoid this problem by creating the url in the server side using an UrlHelper extension method with special placeholders, which could be easily replaced on the client side. I.e. generate an url like this:
http://localhost/Pesquisar/$aaa$/$bbb$/$id$
by providing RouteValues like this: new {aaa="$aaa$, bbb="$bbb$, id="$id$"} to an UrlHelper method. This url can be stored in the value property of a hidden field.
Then, make a browser script for the click event of your button, recover the url with the placeholders from the hidden field, and replace the placeholders with the actual values of the textboxes. To execute the get run this: document.location = theUrl;
If you want to d this for many differnt instances you could create a Helper to geenrate the hidden field with the Url, and a javascript which makes the replacements.
The question is... is it worth the effort?
Can anyone give me a succinct definition of the role of ModelState in Asp.net MVC (or a link to one). In particular I need to know in what situations it is necessary or desirable to call ModelState.Clear().
Bit open ended huh... sorry, I think it might help if tell you what I'm acutally doing:
I have an Action of Edit on a Controller called "Page". When I first see the form to change the Page's details everything loads up fine (binding to a "MyCmsPage" object). Then I click a button that generates a value for one of the MyCmsPage object's fields (MyCmsPage.SeoTitle). It generates fine and updates the object and I then return the action result with the newly modified page object and expect the relevant textbox (rendered using <%= Html.TextBox("seoTitle", page.SeoTitle)%>) to be updated ... but alas it displays the value from the old model that was loaded.
I've worked around it by using ModelState.Clear() but I need to know why / how it has worked so I'm not just doing it blindly.
PageController:
[AcceptVerbs("POST")]
public ActionResult Edit(MyCmsPage page, string submitButton)
{
// add the seoTitle to the current page object
page.GenerateSeoTitle();
// why must I do this?
ModelState.Clear();
// return the modified page object
return View(page);
}
Aspx:
<%# Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<MyCmsPage>" %>
....
<div class="c">
<label for="seoTitle">
Seo Title</label>
<%= Html.TextBox("seoTitle", page.SeoTitle)%>
<input type="submit" value="Generate Seo Title" name="submitButton" />
</div>
I think is a bug in MVC. I struggled with this issue for hours today.
Given this:
public ViewResult SomeAction(SomeModel model)
{
model.SomeString = "some value";
return View(model);
}
The view renders with the original model, ignoring the changes. So I thought, maybe it does not like me using the same model, so I tried like this:
public ViewResult SomeAction(SomeModel model)
{
var newModel = new SomeModel { SomeString = "some value" };
return View(newModel);
}
And still the view renders with the original model. What's odd is, when I put a breakpoint in the view and examine the model, it has the changed value. But the response stream has the old values.
Eventually I discovered the same work around that you did:
public ViewResult SomeAction(SomeModel model)
{
var newModel = new SomeModel { SomeString = "some value" };
ModelState.Clear();
return View(newModel);
}
Works as expected.
I don't think this is a "feature," is it?
Update:
This is not a bug.
Please stop returning View() from a POST action. Use PRG instead and redirect to a GET if the action is a success.
If you are returning a View() from a POST action, do it for form validation, and do it the way MVC is designed using the built in helpers. If you do it this way then you shouldn't need to use .Clear()
If you're using this action to return ajax for a SPA, use a web api controller and forget about ModelState since you shouldn't be using it anyway.
Old answer:
ModelState in MVC is used primarily to describe the state of a model object largely with relation to whether that object is valid or not. This tutorial should explain a lot.
Generally you should not need to clear the ModelState as it is maintained by the MVC engine for you. Clearing it manually might cause undesired results when trying to adhere to MVC validation best practises.
It seems that you are trying to set a default value for the title. This should be done when the model object is instantiated (domain layer somewhere or in the object itself - parameterless ctor), on the get action such that it goes down to the page the 1st time or completely on the client (via ajax or something) so that it appears as if the user entered it and it comes back with the posted forms collection. Some how your approach of adding this value on the receiving of a forms collection (in the POST action // Edit) is causing this bizarre behaviour that might result in a .Clear() appearing to work for you. Trust me - you don't want to be using the clear. Try one of the other ideas.
If you want to clear a value for an individual field then I found the following technique useful.
ModelState.SetModelValue("Key", new ValueProviderResult(null, string.Empty, CultureInfo.InvariantCulture));
Note:
Change "Key" to the name of the field that you want to reset.
Well lots of us seem to have been bitten by this, and although the reason this happens makes sense I needed a way to ensure that the value on my Model was shown, and not ModelState.
Some have suggested ModelState.Remove(string key), but it's not obvious what key should be, especially for nested models. Here are a couple methods I came up with to assist with this.
The RemoveStateFor method will take a ModelStateDictionary, a Model, and an expression for the desired property, and remove it. HiddenForModel can be used in your View to create a hidden input field using only the value from the Model, by first removing its ModelState entry. (This could easily be expanded for the other helper extension methods).
/// <summary>
/// Returns a hidden input field for the specified property. The corresponding value will first be removed from
/// the ModelState to ensure that the current Model value is shown.
/// </summary>
public static MvcHtmlString HiddenForModel<TModel, TProperty>(this HtmlHelper<TModel> helper,
Expression<Func<TModel, TProperty>> expression)
{
RemoveStateFor(helper.ViewData.ModelState, helper.ViewData.Model, expression);
return helper.HiddenFor(expression);
}
/// <summary>
/// Removes the ModelState entry corresponding to the specified property on the model. Call this when changing
/// Model values on the server after a postback, to prevent ModelState entries from taking precedence.
/// </summary>
public static void RemoveStateFor<TModel, TProperty>(this ModelStateDictionary modelState, TModel model,
Expression<Func<TModel, TProperty>> expression)
{
var key = ExpressionHelper.GetExpressionText(expression);
modelState.Remove(key);
}
Call from a controller like this:
ModelState.RemoveStateFor(model, m => m.MySubProperty.MySubValue);
or from a view like this:
#Html.HiddenForModel(m => m.MySubProperty.MySubValue)
It uses System.Web.Mvc.ExpressionHelper to get the name of the ModelState property.
Well the ModelState basically holds the current State of the model in terms of validation, it holds
ModelErrorCollection: Represent the errors when the model try to bind the values.
ex.
TryUpdateModel();
UpdateModel();
or like a parameter in the ActionResult
public ActionResult Create(Person person)
ValueProviderResult: Hold the details about the attempted bind to the model.
ex. AttemptedValue, Culture, RawValue.
Clear() method must be use with caution because it can lead to unspected results. And you will lose some nice properties of the ModelState like AttemptedValue, this is used by MVC in the background to repopulate the form values in case of error.
ModelState["a"].Value.AttemptedValue
I had an instance where I wanted to update the model of a sumitted form, and did not want to 'Redirect To Action' for performanace reason. Previous values of hidden fields were being retained on my updated model - causing allsorts of issues!.
A few lines of code soon identified the elements within ModelState that I wanted to remove (after validation), so the new values were used in the form:-
while (ModelState.FirstOrDefault(ms => ms.Key.ToString().StartsWith("SearchResult")).Value != null)
{
ModelState.Remove(ModelState.FirstOrDefault(ms => ms.Key.ToString().StartsWith("SearchResult")));
}
I wanted to update or reset a value if it didn't quite validate, and ran into this problem.
The easy answer, ModelState.Remove, is.. problematic.. because if you are using helpers you don't really know the name (unless you stick by the naming convention). Unless perhaps you create a function that both your custom helper and your controller can use to get a name.
This feature should have been implemented as an option on the helper, where by default is does not do this, but if you wanted the unaccepted input to redisplay you could just say so.
But at least I understand the issue now ;).
Got it in the end. My Custom ModelBinder which was not being registered and does this :
var mymsPage = new MyCmsPage();
NameValueCollection frm = controllerContext.HttpContext.Request.Form;
myCmsPage.SeoTitle = (!String.IsNullOrEmpty(frm["seoTitle"])) ? frm["seoTitle"] : null;
So something that the default model binding was doing must have been causing the problem. Not sure what, but my problem is at least fixed now that my custom model binder is being registered.
Generally, when you find yourself fighting against a framework standard practices, it is time to reconsider your approach. In this case, the behavior of ModelState. For instance, when you don't want model state after a POST, consider a redirect to the get.
[HttpPost]
public ActionResult Edit(MyCmsPage page, string submitButton)
{
if (ModelState.IsValid) {
SomeRepository.SaveChanges(page);
return RedirectToAction("GenerateSeoTitle",new { page.Id });
}
return View(page);
}
public ActionResult GenerateSeoTitle(int id) {
var page = SomeRepository.Find(id);
page.GenerateSeoTitle();
return View("Edit",page);
}
EDITED to answer culture comment:
Here is what I use to handle a multi-cultural MVC application. First the route handler subclasses:
public class SingleCultureMvcRouteHandler : MvcRouteHandler {
protected override IHttpHandler GetHttpHandler(RequestContext requestContext)
{
var culture = requestContext.RouteData.Values["culture"].ToString();
if (string.IsNullOrWhiteSpace(culture))
{
culture = "en";
}
var ci = new CultureInfo(culture);
Thread.CurrentThread.CurrentUICulture = ci;
Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture(ci.Name);
return base.GetHttpHandler(requestContext);
}
}
public class MultiCultureMvcRouteHandler : MvcRouteHandler
{
protected override IHttpHandler GetHttpHandler(RequestContext requestContext)
{
var culture = requestContext.RouteData.Values["culture"].ToString();
if (string.IsNullOrWhiteSpace(culture))
{
culture = "en";
}
var ci = new CultureInfo(culture);
Thread.CurrentThread.CurrentUICulture = ci;
Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture(ci.Name);
return base.GetHttpHandler(requestContext);
}
}
public class CultureConstraint : IRouteConstraint
{
private string[] _values;
public CultureConstraint(params string[] values)
{
this._values = values;
}
public bool Match(HttpContextBase httpContext,Route route,string parameterName,
RouteValueDictionary values, RouteDirection routeDirection)
{
// Get the value called "parameterName" from the
// RouteValueDictionary called "value"
string value = values[parameterName].ToString();
// Return true is the list of allowed values contains
// this value.
return _values.Contains(value);
}
}
public enum Culture
{
es = 2,
en = 1
}
And here is how I wire up the routes. After creating the routes, I prepend my subagent (example.com/subagent1, example.com/subagent2, etc) then the culture code. If all you need is the culture, simply remove the subagent from the route handlers and routes.
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.IgnoreRoute("Content/{*pathInfo}");
routes.IgnoreRoute("Cache/{*pathInfo}");
routes.IgnoreRoute("Scripts/{pathInfo}.js");
routes.IgnoreRoute("favicon.ico");
routes.IgnoreRoute("apple-touch-icon.png");
routes.IgnoreRoute("apple-touch-icon-precomposed.png");
/* Dynamically generated robots.txt */
routes.MapRoute(
"Robots.txt", "robots.txt",
new { controller = "Robots", action = "Index", id = UrlParameter.Optional }
);
routes.MapRoute(
"Sitemap", // Route name
"{subagent}/sitemap.xml", // URL with parameters
new { subagent = "aq", controller = "Default", action = "Sitemap"}, new[] { "aq3.Controllers" } // Parameter defaults
);
routes.MapRoute(
"Rss Feed", // Route name
"{subagent}/rss", // URL with parameters
new { subagent = "aq", controller = "Default", action = "RSS"}, new[] { "aq3.Controllers" } // Parameter defaults
);
/* remap wordpress tags to mvc blog posts */
routes.MapRoute(
"Tag", "tag/{title}",
new { subagent = "aq", controller = "Default", action = "ThreeOhOne", id = UrlParameter.Optional}, new[] { "aq3.Controllers" }
).RouteHandler = new MultiCultureMvcRouteHandler(); ;
routes.MapRoute(
"Custom Errors", "Error/{*errorType}",
new { controller = "Error", action = "Index", id = UrlParameter.Optional}, new[] { "aq3.Controllers" }
);
/* dynamic images not loaded from content folder */
routes.MapRoute(
"Stock Images",
"{subagent}/Images/{*filename}",
new { subagent = "aq", controller = "Image", action = "Show", id = UrlParameter.Optional, culture = "en"}, new[] { "aq3.Controllers" }
);
/* localized routes follow */
routes.MapRoute(
"Localized Images",
"Images/{*filename}",
new { subagent = "aq", controller = "Image", action = "Show", id = UrlParameter.Optional}, new[] { "aq3.Controllers" }
).RouteHandler = new MultiCultureMvcRouteHandler();
routes.MapRoute(
"Blog Posts",
"Blog/{*postname}",
new { subagent = "aq", controller = "Blog", action = "Index", id = UrlParameter.Optional}, new[] { "aq3.Controllers" }
).RouteHandler = new MultiCultureMvcRouteHandler();
routes.MapRoute(
"Office Posts",
"Office/{*address}",
new { subagent = "aq", controller = "Offices", action = "Address", id = UrlParameter.Optional }, new[] { "aq3.Controllers" }
).RouteHandler = new MultiCultureMvcRouteHandler();
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { subagent = "aq", controller = "Home", action = "Index", id = UrlParameter.Optional }, new[] { "aq3.Controllers" } // Parameter defaults
).RouteHandler = new MultiCultureMvcRouteHandler();
foreach (System.Web.Routing.Route r in routes)
{
if (r.RouteHandler is MultiCultureMvcRouteHandler)
{
r.Url = "{subagent}/{culture}/" + r.Url;
//Adding default culture
if (r.Defaults == null)
{
r.Defaults = new RouteValueDictionary();
}
r.Defaults.Add("culture", Culture.en.ToString());
//Adding constraint for culture param
if (r.Constraints == null)
{
r.Constraints = new RouteValueDictionary();
}
r.Constraints.Add("culture", new CultureConstraint(Culture.en.ToString(), Culture.es.ToString()));
}
}
}
Well, this seemed to work on my Razor Page and never even did a round trip to the .cs file.
This is old html way. It might be useful.
<input type="reset" value="Reset">
In my view the call below generates url ending with Tasks/Edit but I want it to generate url like Tasks/Edit/23
<%= Html.ActionLink<TaskController>("Edit Task", (x) => x.Edit("23"))%>
in Global.asax:
string taskController = NameResolver.NameOfController<TaskController>();
string editAction = NameResolver.NameOfAction<TaskController>(x => x.Edit(null));
routes.MapRoute(
"EditTasks",
"Tasks/Edit/{id}",
new { controller = taskController, action = editAction, id = string.Empty });
I also have binding problem in this action. Values set from view is not binded to my Edit parameter. It comes null everytime and I have not set DefaultModelBinder anywhere. Here is the Edit action:
public ActionResult Edit (string id)
{
//retrieve some data and pass it to view and return view
}
So what can be the problem here? How can I solve url and binding problem? And yes I am a Asp.Net Mvc beginner :)
<%= Html.ActionLink("Task", "Edit", new { id = "2" }) %>
Although why is your id a string and not an int?
I am building a Help Desk Ticket system for a client using ASP.NET MVC 1.0 / C#. I have implemented Steven Sanderson's "App Areas in ASP.NET MVC, Take 2" and it is working great.
In my Globabl.asax page I have some routes defined as such:
public static void RegisterRoutes(RouteCollection routes)
{
// Routing config for the HelpDesk area
routes.CreateArea("HelpDesk", "ProjectName.Areas.HelpDesk.Controllers",
routes.MapRoute(null, "HelpDesk/{controller}/{action}", new { controller = "Ticket", action = "Index" }),
routes.MapRoute(null, "HelpDesk/Ticket/Details/{TicketId}", new { controller = "Ticket", action = "Details", TicketId = "TicketId" })
);
}
So, if I enter "http://localhost/HelpDesk/Ticket/Details/12" in the browser address bar manually, I get the results I expect. Here is my controller:
public ActionResult Details(int TicketId)
{
hd_Ticket ticket = ticketRepository.GetTicket(TicketId);
if (ticket == null)
return View("NotFound");
else
return View(ticket);
}
In my view I have:
<%= Html.ActionLink(item.Subject, "Details", new { item.TicketId } )%>
But that code generates "http://localhost/HelpDesk/Ticket/Details?TicketId=12" which also returns the expected results. My Question is...
How do I define an ActionLink when using Steven Sanderson's Areas that will create a clean URL like: "http://localhost/HelpDesk/Ticket/Details/12" ?
Try
<%= Html.ActionLink(item.Subject, "Details", new { TicketId = item.TicketId } )%>
The ActionLink method expects a dictionary with keys that match the parameter names. (Note that passing an anonymous object is a convenience for this). Anything else I believe it will just tag onto the end of the URL.
EDIT: The reason that this isn't working for you is because your first route matches and takes precedence (controller and action), but defines no TicketId parameter. You need to switch the order of your routes. You should always put your most specific routes first.
Try
<%= Html.ActionLink(item.Subject, "Details", new { TicketId=item.TicketId } )%>
I think Womp has it ...
Oh and while you are swapping your routes try
routes.MapRoute(null, "HelpDesk/Ticket/Details/{TicketId}", new { controller = "Ticket", action = "Details"})
I think the , TicketId = "id" is messing things up
Hope that helps,
Dan
I am trying to create a route with a Username...
So the URL would be mydomain.com/abrudtkhul (abrudtkhul being the username)
My application will have public profiles based on usernames (Ex: http://delicious.com/abrudtkuhl). I want to replicate this URL scheme.
How can I structure this in ASP.Net MVC? I am using Membership/Roles Providers too.
Here's what you want to do, first define your route map:
routes.MapRoute(
"Users",
"{username}",
new { controller = "User", action="index", username=""});
What this allows you to do is to setup the following convention:
Controller: User (the UserController type)
Action: Index (this is mapped to the Index method of UserController)
Username: This is the parameter for the Index method
So when you request the url http://mydomain.com/javier this will be translated to the call for UserController.Index(string username) where username is set to the value of javier.
Now since you're planning on using the MembershipProvider classes, you want to something more like this:
public ActionResult Index(MembershipUser usr)
{
ViewData["Welcome"] = "Viewing " + usr.UserName;
return View();
}
In order to do this, you will need to use a ModelBinder to do the work of, well, binding from a username to a MembershipUser type. To do this, you will need to create your own ModelBinder type and apply it to the user parameter of the Index method. Your class can look something like this:
public class UserBinder : IModelBinder
{
public ModelBinderResult BindModel(ModelBindingContext bindingContext)
{
var request = bindingContext.HttpContext.Request;
var username = request["username"];
MembershipUser user = Membership.GetUser(username);
return new ModelBinderResult(user);
}
}
This allows you to change the declaration of the Index method to be:
public ActionResult Index([ModelBinder(typeof(UserBinder))]
MembershipUser usr)
{
ViewData["Welcome"] = "Viewing " + usr.Username;
return View();
}
As you can see, we've applied the [ModelBinder(typeof(UserBinder))] attribute to the method's parameter. This means that before your method is called the logic of your UserBinder type will be called so by the time the method gets called you will have a valid instance of your MembershipUser type.
You might want to consider not allowing usernames of certain types if you want to have some other functional controllers like Account, Admin, Profile, Settings, etc. Also you might want your static content not to trigger the "username" route. In order to achieve that kind of functionality (similar to how twitter urls are processed) you could use the following Routes:
// do not route the following
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.IgnoreRoute("content/{*pathInfo}");
routes.IgnoreRoute("images/{*pathInfo}");
// route the following based on the controller constraints
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = "" } // Parameter defaults
, new { controller = #"(admin|help|profile|settings)" } // Constraints
);
// this will catch the remaining allowed usernames
routes.MapRoute(
"Users",
"{username}",
new { controller = "Users", action = "View", username = "" }
);
Then you will need to have a controller for each of the tokens in the constraint string (e.g. admin, help, profile, settings), as well as a controller named Users, and of course the default controller of Home in this example.
If you have a lot of usernames you don't want to allow, then you might consider a more dynamic approach by creating a custom route handler.
You could have a route that looks like:
{username}
with the defaults of
Controller = "Users"
For the finished product of:
routes.MapRoute(
"Users",
"{username}",
new { controller = "Users" }
So that the Username is the only url parameter, the MVC assumes it passes it to the users controller.
Are you trying to pass it as a parameter to a Controller?
Theoretically you could do something like this:
routes.MapRoute("name", "{user}/{controller}/{action}", new { controller = "blah", action = "blah", user = "" })
I'm not too experienced with ASP.NET routing, but I figure that should work.
routes.MapRoute(
"Users",
"{username}",
new { controller = "Users", action="ShowUser", username=""});
Ok, what this will do is default the username parameter to the value of {username}
so even though you've written username="" it'll know to pass the value of {username} .. by virtue of the strings match.
This would expect
for the url form
http://website.com/username
Users Contoller
ShowUser Action (method in controller)
username parameter on the ShowUser action (method)