VB.NET namespace abbreviation: How do I make this work in equivalent C# code?

Question

I am a VB.NET programmer by nature and I am having a hard time figuring this out. Any help with the following would be appreciated.

I need to get the C# code (1) below to work. The VB.NET equivalent works just fine, but the C# does not.

Note that both (2) and (3) do work, but this is actually auto-generated code, and I need the VB.NET and C# versions to be as similar as possible.

This does not compile (the fully-qualified name of Engine is ThreeD.QVB.Engine):

using ThreeD.QVB;

namespace QVBScript
{
    public class ScriptCode
    {
        public void Main(ref Engine.QVBObjectsDictionary objects,
                         Engine.Commands commands)
        {
            …

However, this does work:

//using ThreeD.QVB; // I'm instead using fully-qualified names in the method

namespace QVBScript
{
    public class ScriptCode
    {
        public void Main(ref ThreeD.QVB.Engine.QVBObjectsDictionary objects,
                        ThreeD.QVB.Engine.Commands commands)
        {
            …

This works, too:

using eng = ThreeD.QVB.Engine;

namespace QVBScript
{
    public class ScriptCode
    {
        public void Main(ref eng.QVBObjectsDictionary objects, 
                         eng.Commands commands)
        {
            …

Is `ThreeD.QVB.Engine` a namespace containing a type called `QVBObjectsDictionary`, or a type with a nested type? A short but *complete* example would really help. — Jon Skeet, Feb 08 '12 at 19:42
possible duplicate: http://stackoverflow.com/questions/1315256/namespace-references-in-c-sharp-vs-vb-net — M.Babcock, Feb 08 '12 at 19:48
Assuming that you already add reference to it. Try to remove "using ThreeD.QVB;" from 1. and then go to Engine.QVBObjectsDictionary right click and select resolve and see what using statement is added. — atbebtg, Feb 08 '12 at 19:48

score 3 · Accepted Answer · answered Feb 08 '12 at 19:48

In VB.NET if you have an import for the first part of a namespace, you can reference just the later half. In C# you cannot do this. You must have a using for the full namespace, or fully qualify your type names. Different languages, different rules.

In your last example you do not need to use the alias.

using ThreeD.QVB.Engine;

namespace QVBScript
{
    public class ScriptCode
    {
        public void Main(ref QVBObjectsDictionary objects, Commands commands)
        {
            UI.Output Output = (UI.Output)objects["Output"];

Yep, this is the problem and the answer. Not a C# person and trying to hand code the differences. Thanks. — Calphalon, Feb 08 '12 at 20:26

stakx - no longer contributing · Answer 2 · 2012-02-08T20:44:33.273

Basic rules to remember:

`using A.B;`

does allow you to refer to types from namespaces A and A.B without fully qualifying them with their namespace (everywhere in the same file).
does not allow you to abbreviate the names of sub-namespaces of A or A.B. by omitting the A. or A.B. part from their names.

`namespace A.B { … }`

does allow you to refer to types from namespaces A and A.B without fully qualifying them with their namespace (inside the block).
does allow you to abbreviate the names of sub-namespaces of A or A.B by omitting the A. or A.B. part from their names.

Example:

using System.Collections;

namespace A
{
  class Top : IDisposable, // importing System.Collections also imports System   
              IEnumerable, // inside the imported namespace
              System.Collections.Generic.IEnumerable<int>
  {…}                      // ^ "using" does not permit namespace abbreviation
}

namespace A.B
{
  class Middle : Top,      // namespace A available inside namespace A.B
                 C.IBottom // namespace blocks permit namespace abbreviation
  {…}
}

namespace A.B.C
{
  interface IBottom {…}
}

VB.NET namespace abbreviation: How do I make this work in equivalent C# code?

2 Answers2

Basic rules to remember:

using A.B;

namespace A.B { … }

Example:

`using A.B;`

`namespace A.B { … }`