CODEWITHSUNDEEP
c#
andrea
andrea

Reputation: 521

What makes a using directive unnecessary?

What causes the c# compiler to say "using directive is unnecessary" on a using directive?

Presumably current namespace. What else? Is this defined somewhere in the documentation? I couldn't find a definitive answer to a google search.

EDIT to clarify, I'm looking for a list of places where the compiler looks to determine that a directive is not needed.

E.g. current namespace project references

I'm not looking for a simple fix (e.g. remove it) I'm trying to understand why it happens. Pointing me to any documentation that explains it would be awesome.

Upvotes: 3

Views: 20874

Answers (1)

NightOwl888
NightOwl888

Reputation: 56869

"Using directive is unnecessary" means that nothing in the current C# code file is referencing a non-namespace qualified type in the namespace of the using directive. To fix this warning you either need to remove the using directive or add some code that uses a type in the namespace the using statement refers to.

I'm looking for a list of places where the compiler looks to determine that a directive is not needed.

Since namespaces are a assembly-specific thing that can be extended by any assembly, there is no such documented list as it would not have a practical use. However, there are a couple of ways you can find out what types would eliminate the warning message.

In Visual Studio

You can use the Object Browser to determine what types are in a namespace.

enter image description here

Alternatively, you can use Intellisense to get the same information in the code window.

enter image description here

In Code

It is possible to use Reflection to get a list of all types in that namespace in a specific assembly.

string nspace = "...";

var q = from t in typeof(SomeClassInTheAssembly).Assembly.GetTypes()
        where t.IsClass && t.Namespace == nspace
        select t;
q.ToList().ForEach(t => Console.WriteLine(t.Name));

Keeping in mind that a namespace can span several assemblies, this approach could be used to show possible types that could be added to remove the warning.

Upvotes: 7

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