Question

Hello I am new to asp.net. I am confused what is the difference between “using MyNameSpace;” and “namespace MyNameSpace”. My demo code is as follow…

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using MyNameSpace;

namespace MyNameSpace

{
    public partial class DemoPage : System.Web.UI.Page
    {
        My code here
    }
}

In the above code is there any difference between the two highlighted statements or not. If yes then what is it?

Thanks in advance…

Answer 1

Yes, they provide complementary services.

A using directive like this:

using MyNamespace;

Tells the compiler to look in the namespace MyNamespace when resolving simple names – so if you have a type called MyNamespace.Foo, you can just use Foo in your source to refer to it when you’ve got this using directive.

However, the namespace declaration effectively says, “Anything I declare within this block is in the given namespace”. So to declare the MyNamespace.Foo type, you’d use:

namespace MyNamespace
{
    public class Foo
    {
        ...
    }
}

Do you see? The using directive says that you want to use things in a particular namespace, whereas the namespace declaration is about putting things into a particular namespace.