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;
Related
I'm a student learning mainly C++, but this term we have to code our math assignments using C#.
Our professor supplied a basic skeleton program but I'm not very good at C#. He gave us two class files (.cs) but when I add them to my project, I'm unable to utilize them at all. I can't create a class object from either class.
The classes are just Line3d and Point3d. They have the variables needed to compute points and collision.
Thanks for any advice.
Compile your project.
Use Ctrl + . or bulb icon (type your class name you want to use and locate your cursor position over that class name) to resolve namespace for these classes or write using directive manually.
C# classes are normally encapsulated in namespaces. In Visual Studio, adding a new class will generate a file containing a namespace similar to PROJECT_NAME.SUBFOLDER.SUBSUBFOLDER For example:
// MyClass.cs
using System;
namespace MyProject
{
public class MyClass
{
}
}
And then you can reference that from another class in the same namespace, but you can't reference it from a class in another namespace (unless it's a namespace that starts with MyProject.).
// Line3d.cs
using System;
namespace TemplateProject
{
public class Line3d
{
}
}
// MyClass.cs
using System;
namespace MyProject
{
public class MyClass
{
public Line3d LineInstance {get;set;}
}
}
In this example, it won't work because the compiler doesn't know which namespace Line3d exists in (and, indeed, two class with the exact same name could exist in two different namespaces). You need to instruct the compiler to include classes from the TemplateProject namespace (note this doesn't include classes in the TemplateProject.ChildNamespace namespace):
// MyClass.cs
using System;
using TemplateProject;
namespace MyProject
{
public class MyClass
{
public Line3d LineInstance {get;set;}
}
}
Now you should be able to find the Line3d class and use it.
Besides manually referencing the namespace, you can also right-click an unknown class reference, select "Quick actions and Refactorings...", and then you will see something like "using TemplateProject;". Click on this and it will automatically add the using for you.
You can also use the Ctrl+. keyboard shortcut, which does the same as right-click/Quick actions, if you don't want to use the mouse.
select your project and press [ Shift + Alt + A ] to add existing files.
you can see dialog form that allows to open cs file on project.
After that, you can use professor's class files.
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 this abstract class:
using TypeLib=some.type.library;
namespace someSpace
{
abstract class Creator
{
abstract public TypeLib.SomeObject createObject();
}
}
Here's a concrete class:
using TypeLib=some.type.library;
namespace someSpace
{
class SpecialCreator:Creator
{
override public TypeLib.SomeObject createObject()
{
doSomethingSpecial();
return new TypeLib.SomeObject();
}
}
}
Because I will want to implement Creator several different ways, all of which require importing some.type.library because they need to return a TypeLib.someObject, is there a way that I can just have the using statement at some high level and have it be inherited by all the implementations? When I didn't include the using statement in SpecialCreator(), it didn't have access to TypeLib.
EDIT: I think this is different than the duplicate directives question. I'm not trying to consolidate different using statements into one master using that I will then add to many classes; instead, I want to put one using statement in a parent class/header file/static class/etc so that it can be accessible to many classes without having to add the same line of code to each class. Let me know if I've misunderstood the duplicate directives question.
It depends. If TypeLib is only used in base class functionality there is no reason to include 'using TypeLib;' in the files that contain the concrete implementations.
If the desired architecture is intended to encapsulate TypeLib in the abstract base class, the need to have the using statement is an indicator that encapsulation has been broken.
Martin Fowler may say the requirement to 'use' TypeLib in all the concrete implementations is the smell of tight coupling between the class tree under the base class and TypeLib. Using an adapter class may reduce the coupling by putting all TypeLib uses into the adapter.
Not unless you define all classes within a single file.
It depends on what you are trying to do.
If you are just trying to avoid having to add this in each and every page of your derived class, your'd be better off using Visual Studio's Export Template (under the File menu). Pick the Item Template and your added template will show up in the Add > New Item List. I think this would be cleanest.
Of course, there is a sneaky way to do avoid the using itself altogether, but I don't think it's good design. Notice I changed the namespace.
namespace some.type.library;
{
class SpecialCreator:Creator
{
override public SomeObject createObject()
{
doSomethingSpecial();
return new SomeObject();
}
}
}
You could also instead, derive a class in your someSpace namespace from TypeLib.SomeObject (no body for the class) and use this new class wherever you were using TypeLib.SomeObject
using is just a syntactic sugar to save you from typing fully qualified type names each time you type them. It's a hint for compiler for places where to look for type names.
So unless you actually use types from TypeLib you don't have to add using statement in each implementation even if some base class of that concrete implementation uses it in some way (i.e. derives from it). And even if your concrete implementation use types from TypeLib you can avoid using statement by specifying fully qualified type names from that library each time.
You could "alias" the type by creating a child class of it for internal use. For example:
namespace Remote.Namespace
{
public class TypeLib
{
public class SomeObject
{
}
}
}
namespace Internal.Namespace
{
public class InternalTypeLibObject : Remote.Namespace.TypeLib.SomeObject
{
}
}
And now you can use InternalTypeLibObject without having to alias the namespace and cast it to TypeLib.SomeObject.
Now for the drawbacks:
If you want to use the constructors in the parent class, you will need to provide mirror constructors and call the base constructor with constructor chaining. Also, if the parent class is sealed, this won't work.
Honestly though you shouldn't be concerned too much about a little typing. Hiding classes like this can add to confusion and should probably be avoided unless you have a reason to extend the type.
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.