So I made a .dll which I added to my project everything works, but when I try to use any of the class from my .dll. I have to specificly use namespace.classname instead of being able to just say Classname even when I put at the top of my project
using namespace
using System;
using MyTestClassLibrary;
using System.IO;
using YangHandler;
namespace UsingMyclassdll
{
class Program
{
static void Main(string[] args)
{
YangHandler.YangHandler yangh = YangHandler.YangHandler.Parse("Rawtext");
Console.ReadKey();
}
}
}
At the line of using Yanghandler visual studio says
Using directive is unnecessary
Isn't this what using is exactly used for to use other namespaces?
YangHandler code
using System;
using System.IO;
namespace YangHandler
{
public class YangHandler
{
public string YangAsRawText { get; private set; }
public static YangHandler Parse(string YangAsRawText)
{
YangHandler handlerToReturn = new YangHandler();
handlerToReturn.YangAsRawText = YangAsRawText;
return handlerToReturn;
}
I know that it could be solved by using namespace aliases under the namespace "UsingMyclassdll" like
using YangHandler = YangHandler.YangHandler;
But isn't there a more normal solution?
Check this very interesting piece of documentation from Microsoft: https://learn.microsoft.com/en-us/dotnet/standard/design-guidelines/names-of-namespaces
DO NOT use the same name for a namespace and a type in that namespace.
For example, do not use Debug as a namespace name and then also provide a class named Debug in the same namespace. Several compilers require such types to be fully qualified.
So your work around is basically defining the fully qualified name as the type and namespace are of the same name.
No work around for this. The compiler can't know if you mean the one or the other.
Related
When I'm trying to import a namespace from another file, the compiler gives me the error message, "type or namespace name could not be found". Take a look at my code below. Both files are in the same directory, so I don't understand what's wrong.
Setup.cs (the main file)
using System;
using ScreenTextLine; // Error is here.
namespace Setup
{
namespace Screen
{
class Text
{
static void Main(string[] args) { }
}
}
}
Problem.cs (the file with the namespace I'm trying to import)
using System;
namespace Setup
{
namespace ScreenTextLine
{
class WelcomeText
{
static void Main(string[] args){}
}
}
}
You need to use their fully-qualified name when referencing them by separating each namespace by a dot using the following format...
[Top_level_namespace].[nested_namespace]
So, this nested structure...
namespace Setup
{
namespace Screen
{
}
}
It's referenced by a using statement this way...
using Setup.Screen;
I suspect this is a question which has been asked many times before but i haven't found one.
I normally use fully qualified namespaces if i don't use that type often in the file or i add using namaspacename at the top of the file to be able to write new ClassName().
But what if only a part of the full namespace was added ? Why can't the compiler find the type and throws an error?
Consider following class in a nested namespace:
namespace ns_1
{
namespace ns_1_1
{
public class Foo { }
}
}
So if i now want to initialize an instance of this class, it works in following ways:
using ns_1.ns_1_1;
public class Program
{
public Program()
{
// works, fully qualified namespace:
var foo = new ns_1.ns_1_1.Foo();
// works, because of using ns_1.ns_1_1:
foo = new Foo();
}
}
But following doesn't work:
using ns_1;
public class Program
{
public Program()
{
// doesn't work even if using ns_1 was added
var no_foo = new ns_1_1.Foo();
}
}
it throws the compiler error:
The type or namespace name 'ns_1_1' could not be found (are you
missing a using directive or an assembly reference?)
I assume because ns_1_1 is treated like a class which contains another class Foo instead of a namespace, is this correct?
I haven't found the language specification, where is this documented? Why is the compiler not smart enough to check if there's a class or namespace(-part)?
Here's another - less abstract - example of what i mean:
using System.Data;
public class Program
{
public Program()
{
using (var con = new SqlClient.SqlConnection("...")) // doesn't work
{
//...
}
}
}
Edit: now i know why this seems very strange to me. It works without a problem in VB.NET:
Imports System.Data
Public Class Program
Public Sub New()
Using con = New SqlClient.SqlConnection("...") ' no problem
End Using
End Sub
End Class
This obvious way unfortunately not working but you can make all this by an alias namespace:
using ns_1_1 = ns_1.ns_1_1;
public class Program
{
public Program()
{
var no_foo = new ns_1_1.Foo();
}
}
The documentation says:
Create a using directive to use the types in a namespace without having to specify the namespace. A using directive does not give you access to any namespaces that are nested in the namespace you specify.
So the using only includes the types (not the namespaces) that are defined in the specified namespace. In order to access types of nested namespace you need to specify it explicitly with a using directive as you did in your first example.
This is documented in the standard in 3.8 Namespace and Type Names, but it's a bit convoluted to follow.
The gist of it that a partial namespace reference is only looked for in the namespace where it occurs, and each layer outwards. using-directives are not checked.
In your example, ns_1_1.Foo would be found if Foo is found anywhere in:
Program.Program.ns_1_1.Foo
Program.ns_1_1.Foo
ns_1_1.Foo
Partial namespaces will work only if your current class is part of that partial namespace. Using statements are not considered for accessing types through partial namespace.
For instance this will work because your current namespace is ns_1
namespace ns_1
{
public class Program
{
public Program()
{
var no_foo = new ns_1_1.Foo();
}
}
}
I'm trying to understand the c# using directive...Why does this work...
using System;
using System.ComponentModel.DataAnnotations;
namespace BusinessRuleDemo
{
class MyBusinessClass
{
[Required]
public string SomeRequiredProperty { get; set; }
}
}
but this does not?
using System;
using System.ComponentModel;
namespace BusinessRuleDemo
{
class MyBusinessClass
{
[DataAnnotations.Required]
public string SomeRequiredProperty { get; set; }
}
}
The second results in a compile error "The type or namespace DataAnnotations cannot be found. Are you missing are missing a using directive or an assembly reference?
using directive makes it possible to use class names from the namespace you specified as its argument. Since DataAnnotations is not a class, but a namespace, it's not accessible in second case. You should either use fully qulified class names NS1.NS2.Class1, or start you program with using NS1.NS2; and then use Class1.
Because you can either use Fully Qualified Class Names or just use the ClassName and let .NET resolve it via using directive. There is no middle ground.
Class1 -
NameSpace1.NameSpace2.NameSpace3.Class1
can be accessed as
using NameSpace1.NameSpace2.NameSpace3;
...
... Class1.DoSomething();
...
or
...
NameSpace1.NameSpace2.NameSpace3.Class1.DoSomething();
...
but not like
using NameSpace1.NameSpace2;
...
NameSpace3.Class1.DoSomething();
...
In last case what compiler would actually be looking for is root namespace NameSpace3 which clearly does not exist. It won't try to look for System.NameSpace3 or NameSpace1.NameSpace3 or NameSpace1.NameSpace2.NameSpace3 etc etc.
This may be an ignorant question, but I'm unsure why I can not use namespace aliasing and extension methods together.
The following example works just fine:
Program.cs
using System;
using ExtensionMethodTest.Domain;
namespace ExtensionMethodTest
{
class Program
{
static void Main(string[] args)
{
var m = new Domain.MyClass();
var result = m.UpperCaseName();
}
}
}
MyClass.cs
using System;
namespace ExtensionMethodTest.Domain
{
public class MyClass
{
public string Name { get; set; }
}
}
MyClassExtensions.cs
using System;
namespace ExtensionMethodTest.Domain
{
public static class MyClassExtensions
{
public static string UpperCaseName (this MyClass myClass)
{
return myClass.Name.ToUpper();
}
}
}
However, when I alias domain as follows in Program.cs:
using Domain = ExtensionMethodTest.Domain;
The extension method no longer works..
This can be rather frustrating when I'm dealing with converting various domain objects to contract objects (let's say I have 4 domain assemblies and 4 contract assemblies) for use in a web service. Using aliasing would be very handy as I could alias as follows and continue to use the various extension methods (such as ToContract, etc.):
using BillingContracts = Namespace.Billing.Contracts;
using IssuingContracts = Namespace.Issuing.Contracts;
etc...
I look forward to the answer.. I'm sure it's straight forward, but I, for the life of me, can't figure out why it doesn't work.
Thanks!
Make sure to still add a non-aliased using statement:
Program.cs
using System;
using ExtensionMethodTest.Domain; //DON'T FORGET A NON-ALIASED USING
using MyDomain = ExtensionMethodTest.Domain;
namespace ExtensionMethodTest
{
class Program
{
static void Main(string[] args)
{
var m = new MyDomain.MyClass();
var result = m.UpperCaseName();
}
}
}
MyClass.cs
using System;
namespace ExtensionMethodTest.Domain
{
public class MyClass
{
public string Name { get; set; }
}
}
MyClassExtensions.cs
using System;
namespace ExtensionMethodTest.Domain
{
public static class MyClassExtensions
{
public static string UpperCaseName (this MyClass myClass)
{
return myClass.Name.ToUpper();
}
}
}
I also love to use namespace aliasing but its not working in case of Extension methods. So one thing that i did is, I changed the namespace of extension class to same namespace that my main project has (although my extension class resides in sub folder of main project).
Suppose I have a project myFirstProj which surely has namespace myFirstProj for root classes. My extension class is present in myFirstProj/Common/myExtensionClass with contains namespace myFirstProj.Common { //myExtensionClass }.
So now what I did is, I changed the namespace of myExtensionClass from namespace myFirstProj.Common{ //myExtensionClass } to namespace myFirstProj{ //myExtensionClass } .
Now i can use my extension methods in my whole project myFirstProj event without specifying using statement for my extension class.
I know this isn't a standard way to that but I haven't found any other workaround for it expect this one because for my Project there is a requirement to go with namespace aliasing for project namespaces.
How is it possible that .NET is finding the wrong 'MyType' in this scenario?
I have a type A.B.C.D.MyType in a project that I'm working on, and I'm referencing a DLL that has a type A.B.MyType? I do not have any 'using A.B;' statements anywhere in my code, and I do have 'using A.B.C.D;'. When I compile, the compiler thinks any naked reference to 'MyType' means 'A.B.MyType'.
I know I could just rename the class or use an alias, but I'm wondering how this is even possible.
Any ideas?
Thanks!
Are you working in a namespace that is under A.B namespace? (for example A.B.X) if so the C# namespace resolutions (ECMA-334 C# Language Specification : 10.8 10.8 Namespace and type names) says:
... for each namespace N, starting
with the namespace in which the
namespace-or-typename occurs,
continuing with each enclosing
namespace (if any), and ending with
the global namespace, the following
steps are evaluated until an entity is
located...
and then followed by:
If K is zero and the namespace
declaration contains an
extern-alias-directive or
using-aliasdirective that associates
the name I with an imported namespace
or type, then the
namespace-or-type-name refers to that
namespace or type
This means that name resolution starts at the current namespace and searches all namespaces up to the root, and only after this hierarchical search ends, then the namespaces imported with the using clause are searched.
The following example prints "Ns1.Foo"
using Ns1.Foo.Foo2;
namespace Ns1.Foo
{
class Foo
{
public void Print()
{
System.Console.WriteLine("Ns1.Foo");
}
}
}
namespace Ns1.Foo.Foo2
{
class Foo
{
public void Print()
{
System.Console.WriteLine("Ns1.Foo.Foo2");
}
}
}
namespace Ns1.Foo.Bar
{
class Bar
{
public void Print()
{
new Foo().Print();
}
static void Main()
{
new Bar().Print();
}
}
}
Edit: Adding a using clause inside a namespace, will make so that the namespace is searched before the hierarchical search of current namespace is done is done. Change the example to:
namespace Ns1.Foo.Bar
{
using Ns1.Foo.Foo2;
class Bar
{
public void Print()
{
new Foo().Print();
}
static void Main()
{
new Bar().Print();
}
}
}
and Ns1.Foo.Foo2 will be printed.
Edit: changed example
Is your code in namespace A.B or A.B.C? If so, that's probably the issue. Use a using directive like this:
using TheTypeIWant = A.B.C.D.MyType;
then just refer to TheTypeIWant in your code.
EDIT: I've just tried the "using MyType=A.B.C.D.MyType" option, but that doesn't work. The above is fine though.
Just a guess: in your project properties, is the "default namespace" set to A.B ?