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What makes a particular using directive unnecessary?

I have a solution with multiple projects.
Project A has namespace 1 which uses a particular class X and has a using directive for it. That project compiles.
Project B has class 2 (in namespace 2) which uses the same class X but does not compile because "The name X does not exist in the current context". If I include the using directive from class 1 I get "Using directive is unnecessary"
So there is something different about project A and B, where one needs the using directive and one doesn't.
There are clearly multiple issues with my solution here but first I want to understand what makes a using directive necessary or not. Where can I start looking?
Edited to clarify the text above a bit, and also add the following code snippets as requested.
Project A:
using Microsoft.WindowsAzure; //CloudConfigurationManager is here
using MyNamespace.MyClass; //Constants is here
namespace n1
{
private static string resourceId = CloudConfigurationManager.GetSetting("id");
Console.WriteLine($"{resourceId}{Constants.Blah}("blah")";
}
Project B:
using Microsoft.WindowsAzure; //directive unnecessary
using MyNamespace.MyClass; //directive unnecessary
namespace Testing
{
class Program
{
public static void Main(string[] args)
{
string resourceId = CloudConfigurationManager.GetSetting("id"); // The name CloudConfigurationManager does not exist in the current context
Console.WriteLine($"{resourceId}{Constants.Blah}("blah")"; // The name Constants does not exist in the current context
}
}
}

You need to add the using X class X in your Project B separately. Your using X from Project A isn't forwarded by only adding a using A.
If you would only use functions/classes from Class 1, which encapsulate functionality of class X you would be OK with only referencing class 1.
But in your case, as I understand it, you want to use X-functionality directly - hence the separate using directive.

namespaces and using scope resolution [duplicate]

This question already has answers here:
C#: Difference between using System.Text and System.Text.RegularExpressions
(3 answers)
Nested namespaces
(6 answers)
Using nested namespaces [duplicate]
(3 answers)
Closed 5 years ago.
I have run across something I find odd in C# .NET Core 2.0 and I am wondering what is going on here.
I have a file called FooBar.cs and it looks like this
namespace Foo
{
public class FooClass
{
}
namespace Bar
{
enum BarEnums
{
Bar1
,Bar2
,Bar3
}
}
}
And I have a simple program that looks like this
using System;
using Foo;
namespace Using
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
FooClass fooClass = new FooClass();
Console.WriteLine(Bar.BarEnums.Bar1);
}
}
}
This gives me the following error:
Program.cs(16,22): error CS0103: The name 'Bar' does not exist in the current context
I am confused as to why the using statement exposes the class within the name space but it does not expose the namespace also found at the same level? If I put in using Foo.Bar it still gives the same error.. so the using statement can see the namespace but it does not help it find the references below.
Now if I put in Foo.Bar.BarEnums.Bar1 it will work just fine.. But why do I not have to put in Foo.FooClass following the same nomenclature as with the reference to the enums? Is this just a difference between accessing enums vs classes from within a namespace?

That happens because using Foo only imports the types contained in the given namespace, but it does not specifically import the nested namespaces. So that´s why when you reference your enum you have to do it with the full namespace reference.
This is a C# language specification.
Here is an explanation from a guy from the C# team:
In C#, when you specify a “using” clause, such as
using System.Text;
the compiler only imports the types in System.Text into the global
namespace – it doesn’t do the same with any namespaces inside of
System.Text. So, while that using allows me to write:
StringBuilder s = new StringBuilder();
it does not allow me to write:
RegularExpressions.Regex r = new RegularExpressions.Regex();
Why?
Well, an early version of the C# compiler had that behavior, but we
found that it had a few issues:
First, it made the code harder to follow. In the above example,
RegularExpressions.Regex() could be a global name, or a name based on
any of my using clauses. Having to look at the top of your code to
figure out what a name is is something we’d like to avoid.
The second problem had to do with collisions between namespace names,
which occurred much more often with this behavior. If there was
another namespace with a RegularExpressions namespace inside of it,
the user wouldn’t be able to have a “using” statement for both – even
if they didn’t actually care about that namespace.
We therefore decided to change the behavior.
https://blogs.msdn.microsoft.com/csharpfaq/2004/03/07/why-dont-namespace-using-directives-import-nested-namespaces/
And here is the C# spec: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/namespaces

'Class' is a namespace but is used like a 'type'

First, this is not the same as the many highly upvoted questions on this exact topic unless I'm missing one of them. All of them point that the issue is I have a namespace with the same name as the class. This is not the case (but it was).
I started out creating a new console application called BatchResizer and put a couple of classes there, but then decided to move this into a class library, called BatchResizer.Components; I then renamed the original console application to BatchResizer.ConsoleRunner, changed all classes in that project to namespace BatchResizer.ConsoleRunner.[...], set the assembly name and default namespace to the same.
There is a class titled BatchResizer but there are no namespaces titled [...].BatchResizer in the project anymore, but when I do var batchResizer = new BatchResizer() I get the error that the namespace is used like a class. There are items named like BatchResizer.ConsoleRunner.[...] or BatchResizer.Components.[...], but nothing ending in BatchResizer.
I've tried "cleaning" and rebulding the project, deleting the .suo file, deleting the /bin folder of all projects in the solution, and I've went through every class in all related projects for namespace collisions.

BatchResizer is still a namespace name, though. If it's also the same name as a class, you'll have to be more explicit:
var batchResizer = new Components.BatchResizer();
You could also add a using statement within your namespace:
namespace BatchResizer.ConsoleRunner
{
using Components;
internal class Program
{
private static void Main(string[] args)
{
var batchResizer = new BatchResizer();
}
}
}
If you want to get a bit geeky, then the C# 5.0 spec has this to say:
9.2 Namespace declarations
...The qualified-identifier of a namespace-declaration may be a single identifier or a sequence of identifiers separated by “.” tokens. The latter form permits a program to define a nested namespace without lexically nesting several namespace declarations. For example,
namespace N1.N2
{
class A {}
class B {}
}
is semantically equivalent to
namespace N1
{
namespace N2
{
class A {}
class B {}
}
}
So even if, as you say, no class is declared in the namespace BatchResizer, BatchResizer is declared as a namespace.

First, this is not the same as the many highly upvoted questions on this exact topic unless I'm missing one of them. All of them point that the issue is I have a namespace with the same name as the class. This is not the case (but it was).
BatchResizer may not be a 'final' namespace, but it' still a namespace
Namespace : Foo.BatchResizer.Components
Foo.BatchResizer.ConsoleRunner
Class : Foo.BatchResizer

C#: Problem trying to resolve a class when two namespaces are similar

I'm running into an issue where I can't make a reference to a class in a different namespace. I have 2 classes:
namespace Foo
{
public class Class1 { ... }
}
namespace My.App.Foo
{
public class Class2
{
public void SomeMethod()
{
var x = new Foo.Class1; // compile error!
}
}
}
The compile error is:
The type or namespace name 'Class1'
does not exist in the namespace
'My.App.Foo'
In this situation, I can't seem to get Visual Studio to recognize that "Foo.Class1" refers to the first class. If I mouse-over "Foo", it shows that its trying to resolve that to "My.App.Foo.Class1"
If I put the line:
using Foo;
at the top of the .cs file that contains Class2, then it also resolves that to "My.App.Foo".
Is there some trick to referencing the right "Foo" namespace without just renaming the namespaces so they don't conflict? Both of these namespaces are in the same assembly.

You can use global:: to globally qualify a namespace: global::Foo.Class1 should work,.
You could also alias global::Foo to make things easier. At the top of your source file, below your using statements, add:
using AliasClass1=global::Foo.Class1;
Now you can use:
AliasClass1 c = new AliasClass1();
// and so on.
Of course, you can use a better name than AliasClass :-)

var x = new global::Foo.Class1();

In addition to LBushkin's answer, you might be interested in these articles by Eric Lippert :
Do not name a class the same as its namespace, Part One
Do not name a class the same as its namespace, Part Two
Do not name a class the same as its namespace, Part Three
Do not name a class the same as its namespace, Part Four
They are not directly related to your problem, but they give an interesting insight on naming strategies

C# directives & namespace problem

I have a problem here. I have a class library namely ClLib, and has the following 8 cs files.
Express (parent class)
- 1E1
- 1E2
- 1E3
Normal (parent class)
- 1N1
- 1N2
- 1N3
Also, a method is also included in each 8 class file. For example,
public class 1E1:Express
{
public int subtractNumExp1E1(int firstNum, int secNum)
{
return firstNum - secNum;
}
}
The 1E1:Express is used to display the relationship between the parent class(Express) and subclass (1E1).
I have also created a Windows App in Visual Studio, and I need to create a directive like "using ClLib.Express.1E1". How do I go about it? I am stuck in this situation whereby when I want to change the namespace of 1E1 from "namespace ClLib" to "namespace ClLib.Express.1E1". An error occurs, as the namespace ClLib has already contain one definition for Express.
A great thanks and appreciation in advance for all kind souls who are willing to help me:)

You can't have a type and a namespace with the same name ("CILib.Express").
If you want a CILib.Express namespace, the simplest option is to move/rename the CILib.Express type.
You can, however, also have nested types. You could, for example, have:
namespace CILib {
public class Express {
public class SomeType {}
}
}
If separate files are a concern:
file 1:
namespace CILib {
public partial class Express {
// "Express" code
}
}
file 2:
namespace CILib {
public partial class Express {
public class SomeType {
// "SomeType" code
}
}
}
However, using directives only relate to namespaces; I don't think you could have using CILib.Express, as that is a type not a namespace.

In that case you just have to delete the namespace ClLib and make sure that there is exactly one copy of ClLib.Express.1E1
P/S: Are you sure that the proper namespace is ClLib.Express.1E1? 1E1 is a cs file, and it's usually a class. So you don't have to write using ClLib.Express, that would be sufficient.

I think there is confusion around the namespace and base class.
Namespace: ClLib.Express
Class: public class 1E1:Express
Rename your base class to ExpressBase to differentiate it.
If you need to reference the namespace:
using ClLib.Express
Hope I have understood your project structure!