Why use "new" for Route Values in "ActionLink" ---- for example - asp.net-mvc

Question

I have 2 examples below:
#Html.ActionLink("Create New", "Create", new { id = Model.Id })
and,
return RedirectToAction("Index", new { id = review.RestaurantId });
My question is regarding the new { id = xxx} part in object route values. Why do we use "new" in this case? What exactly does it do? Does it initialize "id" variable in this case?
Also, it is strange that these methods, create and index definition can only take arguments as defined in the route values...
That is,
public ActionResult create { int id)
{ ...}
is correct but following is wrong....
public ActionResult create { int somethingelse)
{ ...}
So please tell me what is the new {id = xx} in my first 2 examples is doing?
Thanks

Answer 1

new {} creates a new object of type Object. The type is anonymous. You see that syntax when writing linq queries that end in " select new {x = "foo". y="bar"}". It is often used when setting an object to type "var".
What you are doing in your ActionLink is providing Route Values. MVC takes the properties and values in the object and puts them in the QueryString of the request. It is what you might refer to as "magic". You can set a break point in your controller Action and check "HttpContext.Request.QueryString" to see it.
The input values for you Action methods have to match the properties that are being passed in via the QueryString.

Answer 2

That is actually creating an anonymously typed object and passing it into ActionLink(). ActionLink then uses that object, coupled with your routing rules to generate the link. MVC will look for properties on that object that match the routing names (usually of route parameters) and figure out how to build it. Since you likely have the default MVC route (/controller/action/{id}) that is what links everything together.
Further, that is why id "is correct", but somethingelse "is wrong".
If you change "id" to "somethingelse" in your routing rule, you could then see new { soemthingelse = ""} work in your ActionLink().
Does that help?

Answer 3

In both cases your creating a new anonymous object to pass into the query string as a route value. You create a new object because one does not already exist on the view.
The MVC source code:
if (additionalViewData != null) {
foreach (KeyValuePair<string, object> kvp in new RouteValueDictionary(additionalViewData)) {
viewData[kvp.Key] = kvp.Value;
}
}
They use it to create new RouteValueDictionary parameters.
You don't have to use it the this manor. You could create an object on the model and pass it in:
public class SomeModel
{
public SomeModel()
{
MyObject = new { id = 10 };
}
public int Id {get;set;}
public object MyObject {get;set;}
}
#Html.ActionLink("Create New", "Create", Model.MyObject)
This would also work though is probably not something you would attempt.
For the second part of your question. The RouteValueDictionary searches by key and assigns the value to the key that was given.
So whatever you call the key in the anonymous object, MVC will attempt to assign the value to it on the action. The name must match or they key cannot assign the value.