有关Html.ActionLink帮助器的问题-特别是对象routeValues参数的语法

Question

So I understand the use of the ActionLink HTML helper, as well as most of the parameters. I am still in the process of wrapping my head around the complete range of uses for the object routeValues parameter.

However, my question is that it seems for the routeValues parameter you could specify the object as either the existing object from the ViewData dictionary:

Html.ActionLink("Some Text", "Edit", Model.ProductId);

or you can use object initializing syntax:

Html.ActionLink("Some Text", "Edit", new { Model.ProductId });

My 2 questions, are

A) what is the defining reason to use one over another? I have a hard time understanding why you have to initialize a new one since you already have the property with the correct value in the Model.

B) I understand instantiating a new object (ie var someVar = new SomeObject()), but what are you defining in the above example ( new { Model.ProductID }) and your specifying a property?

Thanks,

Answer 1

You may want to send other values to the controller action

Example:

Html.ActionLink("Some Text", "Edit", new { id=Model.ProductId, myotherValue=1 });

And your control action is something like this

Public ActionResult Edit(int id, int myotherValue);

Answer 2

AFAIK, both of those are incorrect. When you specify an object that isn't a RouteValueDictionary (typically an anonymous object), it transfers the property/value pairs into the dictionary by using reflection over the properties of the object. In neither case you use will you get an object that translates into a RouteValueDictionary containing an id key with an associated value. In the second case, I don't think you even have legal syntax it won't map correctly onto the id parameter given the default routes. The syntax that you want is:

Html.ActionLink("Some Text", "Edit", new { id = Model.ProductId } );

You're creating an anonymous object with an id property whose value is Model.ProductId . This will result in a RouteValueDictionary with an id key that maps onto the value of Model.ProductId .

Answer 3

B) syntax new { id = 1, name = "11" } means "create anonymous object". During build process compiler finds all such usages and creates classes with unreadable names in your assembly like this:

class AnonymousType`1
{
    int id {get; private set};
    int name {get; private set};
}

then all references change to code like this new <>AnonymousType`1{ id = 1, name = "11" } It is just a description of how it works, generated code is a little more complex.

A) So you see, that Model.ProductId is int, and new { Model.ProductId } is instance of some type, generated by compiler.

You could examine this using Reflector. More info about Anonymous Types