Does the name of namespace also define the scope in the class?
For example, I have namespace that is named by solution by default. Lets say in Program.cs name of namespace is "MySolution".
in the next file interface that I have created, name of namespace is "Interfaces"
When I go back to class, to implement this interface, it was not in the scope (I could not find it in intellisense). So if class has one namespace, and interface has second namespace, than I cant use it in my class.
I thought namespace is only used to organise classes (like a surname), but I guess it also defines a scope.
"The namespace keyword is used to declare a scope that contains a set of related objects. You can use a namespace to organize code elements and to create globally unique types." https://msdn.microsoft.com/en-us/library/z2kcy19k.aspx
To use a class, interface, struct, enum, delegate from another namespace, you will need to use the fully qualified name of the type, or declare a reference to that namespace with using Interface; at the top of your class. IE:
using Interfaces; //can reference namespaces here
namespace MySolution
{
public class Program
{
//or you can use the fully qualified name of the type
public Program(Interfaces.MyInterface example)
{
}
}
}
Related
I was wondering Why I can access class when I defined it outside of namespace scope?
I am not very familiar with namespaces, I am just learning, but I thought that namespace should like wrap all my classes to one 'box' and they can access each other just inside that 'box' (scope).
Code example:
class Point
{
public int X;
}
namespace ConsoleApplication12
{
class Program
{
static void Main(string[] args)
{
Point p = new Point();
p.X = 50;
Console.WriteLine(p.X);
Console.ReadLine();
}
}
}
Thank you for answers.
Namespaces have nothing to do with access. It's important to differentiate between namespaces and assemblies - they're often closely related, in that types in a namespace Foo.Bar would be likely to be in assembly Foo.Bar.dll, but that's a convention - it's not something the compiler or language cares about.
A namespace is primarily "a space in which names have to be unique". In other words, while it's fine to have two types called Point in different namespaces, you can't have two types called Point in the same namespace. Indeed, the primary reason for namespaces existing (IMO) is so that we don't all have to use completely unique names across every piece of .NET code in the world.
You can use your Point class which is implicitly internal so long as it's declared within the same assembly. If it's in the global namespace (i.e. not declared in a namespace at all) then you don't need any using directives to refer to it - the purpose of a using directive is to allow you to refer to members of a different namespace just by their short name.
So if you have:
namespace Foo.Bar
{
public class Baz {}
}
then you could access that as either:
namespace Other
{
class Test
{
Foo.Bar.Baz baz = new Foo.Bar.Baz();
}
}
or
// Allow anything in namespace Foo.Bar to be accessed by its
// short name
using Foo.Bar;
namespace Other
{
class Test
{
Baz baz = new Baz();
}
}
If the type is defined in the "global" namespace, then you just don't need the using directive. From the C# 5 language specification section 3.8 (namespace and type names) where it's describing the type name lookup procedure:
If the previous steps were unsuccessful then, for each namespace N, starting with the namespace in which the namespace-or-type-name occurs, continuing with each enclosing namespace (if any), and ending with the global namespace, the following steps are evaluated until an entity is located
So in your case, looking for Point from your Main method, first ConsoleApplication12 would be checked for a Point type, then the global namespace.
To access class, outside namespace, your class should be public
public class Point
and in your namespace, where you want to see this class, you need to add namespace in top of usings
using mynamespace.external;
Than you can access your class
I have a few differenet namespaces in my solution and I want to use an object called "Doctor" from namespece BL_Backend inside another namespace called DAL. I've tried adding a Refference to DAL (a refference for BL_Backend), and then adding "using BL_Backend;" but it wouldn't work. still classes such as Doctor won't appear as known ones inside namespace DAL.
namespace BL_Backend
{
…
namespace DAL
{
…
//Here create object as "Doctor" for BL_Backend class
}
}
For example,
when i call a constructor of a doctor from DAL it says this constructor does not exists but when i write the exact same command at namespace bl_backend it works fine.
thanks alot!
I assume Doctor is declared as internal class in BL_Backend assembly. Note - if class does not have public access modifier, then by default it will be internal:
namespace BL_Backend
{
class Doctor // this class is internal
{
}
}
Internal classes are visible only within assembly they are defined (well, there is attribute InternalsVisibleTo which allows other assemblies to see internal classes, but without applying this attribute, class is not visible to other assemblies).
If you want to use a class Doctor from an assembly BL_Backend in a DAL you must add a reference in DAL to the BL_Backend not vise versa.
Classes without a modifier are internal by default, so ensure that your modifier is public.
As a second option pay attention to the build order - its not a problem in VS12+ anymore, but in further versions it was.
I am writing code for a game, and wanted to include my main method in two different namespaces so that it could easily access all the classes from both the 'Engine' and 'Core' Namespaces.
namespace Engine Core
{
class ExampleClass
{
}
}
Although I just put a space between Engine and Core, I know that this syntax is incorrect, I would like to know how to make a class a member of multiple namespaces. If this is not possible, is there anything that I could do that would act the same? (Classes in neither these two namespaces having to refer to this class by 'Engine.' or 'Core.'
A class can not belong to two different namespaces.
If you want to refer to a class of the Engine or Core namespaces without explicitly writing the namespace each time you reference a type of those namespaces, just use using at the beginning of the file. The using directive allows the use of types in a namespace so that you do not have to qualify the use of a type in that namespace:
using Engine;
or
using Core;
Check the documentation: using Directive
So you want someone to be able to access ExampleClass by using Engine.ExampleClass and Core.ExampleClass? I'm not sure why you would (I'm sure you have your reasons) but two ways to expose something like this are:
namespace Foo
{
abstract class ExampleClass
{
//Only implement the class here
}
}
namespace Engine
{
class ExampleClass : Foo.ExampleClass
{
//Don't implement anything here (other than constructors to call base constructors)
}
}
namespace Core
{
class ExampleClass : Foo.ExampleClass
{
//Don't implement anything here (other than constructors to call base constructors)
}
}
Or you could use namespace aliasing but every cs file using the class would require the alias to be defined.
using Engine = Core;
Okay, there's System and System.Web. Am I correct in that the structure this suggests is:
namespace System
{
// all of the outer namespace members
namespace Web
{
// all of the inner members
}
}
And that when a namespace is nested within another, having a using directive with the parent/outer namespace only doesn't automatically bring in the child/nested namespace? In other words:
using System;
public class Example
{
public Example()
{
context1 = new HttpContext(); // won't work
context2 = new System.Web.HttpContext(); // will work
}
}
Just trying to see if I actually understand this correctly.
System.Web is declared as:
namespace System.Web
{
public class HttpContext {}
}
However, it would be possible to actually declare a child namespace:
namespace System
{
namespace Web
{
public class HttpContext {}
}
}
I have never seen something like this but the syntax allows it and the effect is the same. In both cases, the namespace of HttpContext is System.Web.HttpContext.
Even with the second example, using System; wouldn't import the child namespace, only the types defined in that namespace are imported.
You could nest namespaces and any using directive would only grant access to the members defined within the specific namespace you are referencing.
So from your example:
namespace System
{
// all of the outer namespace members
namespace Web
{
// all of the inner members
}
}
Referencing System would grant you access to the outer namespace members and referencing System.Web would grant you access to all of the inner namespace members.
But this is atypical and usually namespaces are defined only once within a file. The dot-notation typically follows a folder or project structure, so files that were nested as such:
WebApplication
- Models
- MyModel.cs
- Controllers
- MyController.cs
Might use namespaces of WebApplication.Models and WebApplication.Controllers.
I can't think of a great example off the top of my head where you would want to nest namespaces, but there may be a good reason to. However, it would be considered an exception to the rule, in my opinion.
Yes, a using directive only allows types declared in that namespace to be used without namespace qualifier. Nested namespaces are not automatically included.
As Daniel said, System.Web is not declared separately. System and System.Web are two separate namespaces which are technically unrelated.
That's why your code example of new HttpContext() won't work - because HttpContext is not in the System namespace at all.
this is a common confusion regarding composite namespaces. Heres a great article of microsoft about it: http://msdn.microsoft.com/en-us/library/ms973231.aspx
I have a webservice project with a class (let's refer to it as webservice.classA).
I have another class project producing a dll which references that class in its own namespace and instantiates an instance of it (lets call the dlls namespace dllnamespace).
In another project I want to access the member in the dll
e.g.
using webservice;
namespace other_project
{
class B
{
classA copy = null;
//....
dllnamespace.dostuff(); // amongst other things instantiates a classA object
//....
copy = dllnamespace.getclassA(); // method to return classA member
The compiler error I get is cannot convert type from dllnamespace.webservice.classA to other_project.webservice.classA
I guess I have a fundamental design flaw but I figure there must be (?) a way to declare/use "webservice.classA" in more than one namespace.
You have a name clash. The supported way of avoiding this (short of not naming your classes the same), is to define a using alias for one of the classes:
using webservice.classA = myWebserviceClassA;
You are right...the design flaw does exist in terms of naming.
Let us assume:
you have a class named
MyClass
the class exists both in namespace- abc.xyz.qwe.tyu.MyClass
and in namespace - sed.qwe.dfg.ert.MyClass
The workaround is -
using NS1 = abc.xyz.qwe.tyu.MyClass;
using NS2 = sed.qwe.dfg.ert.MyClass;
This way you avoid the clash.
Also, helpful to use if you have very long namespaces.
FURTHER REFERENCE : (From MSDN article on using Directive )
The scope of a using directive is
limited to the file in which it
appears.
Create a using alias to make it easier to qualify an identifier to a
namespace or type.
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.
Change the copy definition line to:
dllnamespace.webservice.classA copy = null;
That's just the problem - you cannot have a class in more than one namespace. This is what namespaces were designed for - to prevent classes with the same name written by different people from aliasing. You'll need to decide for one of your namespaces to own that class and in the other one to import it. Alternatively if the dll and the web service are part of the same distributed app then they should use the same namespace.