How can I prevent use of a class from outside its namespace in C#?
For example, I have two namespaces. One defines a data model class, the other defines a data model class which inherits the first. The second namespace also defines a utility class which is the only class to be allowed to use the second data model class..
namespace A
{
public class ModelA {} // can be used by any class
}
namespace B
{
class ModelB : ModelA {} // can only be used by Utility
public class Utility
{
public void DoSomething()
{
var item = new ModelB {};
...
}
}
}
By implementing the following code in another class library or project, I would like the effect indicated by the comments...
namespace C
{
public class Stuff
{
public void DoThings()
{
var a = new ModelA(); // this should work
var b = new ModelB(); // this should not work
}
}
}
You can not add a private access modifier to classes that are directly contained in a namespace.
You can however make ModelB a private nested class:
namespace A
{
class ModelA {} // can be used by any class
}
namespace B
{
class Utility
{
private class ModelB : ModelA {} // can only be used by Utility
public void DoSomething()
{
var item = new ModelB {};
...
}
}
}
which means that, like any other private property, it cannot be accessed outside of the Utility-class
Related
I have a bunch of derived classes that inherit from a base class. Each derived class still has unique members. One of these derived classes needs to be able to access all the other derived class's members. My aim with this problem is to write as little code as possible.
Would it be sloppy or bad practice to initialize all the derived classes' members in the base class so that one of the derived classes can access those members, instead of initializing them in said derived class?
Proposed approach:
public class BaseClass {
public BaseClass() {
...
der1Initializer = Der1Initializer(new Factory1());
der2Initializer = Der1Initializer(new Factory2());
List initializers = new List(){ der1Initializer , der2Initializer };
der3Initializer = Der3Initializer(initializers);
}
Der1Initializer der1Initializer;
Der2Initializer der2Initializer;
Der3Initializer der3Initializer;
}
public class DerivedClass1 : BaseClass {
public SomeFunction {
der1Initializer.init();
}
}
public class DerivedClass2 : BaseClass {
public SomeFunction {
der2Initializer.init();
}
}
public class DerivedClass3 : BaseClass {
...
}
So that:
public class Der3Initializer {
public GroupInitializationFunction {
initializers[0].init(); //der1Initializer
initializers[1].init(); //der2Initializer
}
}
Instead of:
public class BaseClass {
public BaseClass() {
...
}
public class DerivedClass1 : BaseClass {
public DerivedClass1 {
der1Initializer = Der1Initializer(new Factory1());
}
public SomeFunction {
der1Initializer.init();
}
Der1Initializer der1Initializer;
}
public class DerivedClass2 : BaseClass {
public DerivedClass2 {
der2Initializer = Der2Initializer(new Factory2());
}
public SomeFunction {
der2Initializer.init();
}
Der2Initializer der2Initializer;
}
public class DerivedClass3 : BaseClass {
public DerivedClass3 {
List initializers = new List()
{
Der1Initializer(new Factory1()),
Der2Initializer(new Factory2());
};
der3Initializer = Der3Initializer(initializers);
}
...
Der3Initializer der3Initializer;
}
...
public class Der3Initializer {
public GroupInitializationFunction {
initializers[0].init(); //der1Initializer
initializers[1].init(); //der2Initializer
}
}
This is a vast oversimplification of the "problem". The purpose of this code is to reduce duplicate code and the need to reinitialize members that can be shared and to optimize performance.
I am aware that it isn't necessarily a good idea to give other classes access to members they aren't using.
I just thought this is an interesting problem regarding code separation vs. duplicate code.
I would not recommend initializing childs on the parent class as
Violates Open Closed Principle as the base class has the responsibility of initializing its children and there will always be the need to add new child classes and consequently modifying base class .
Violates Single Responsibility Principle as this is not the role for the base class (to initialize its childs )
Violates Inversion of Control as base class is tightly coupled to child class see this link
I have a class in a folder in my namespace as:
using System;
namespace mynamespace.myFolder1
{
public class F1
{
// class properties...
// class methods...
public class F1_Nest
{
// class properties...
// class methods...
}
}
Now I have to access class F1_Nest as from:
using System;
using mynamespace.myFolder1;
namespace mynamespace.myFolder2
{
public class F2
{
// class properties...
// class methods...
// I have to access nested class F1_Nest here...
}
}
How will I use/access class F1_Nest inside class F2?
A nested class is just like a normal class, except it's definition resides within the containing class. The result is that the containing class is almost like a namespace for the nested class. You don't have to instantiate the containing class in order to use the nested class. For instance:
namespace MyNamespace
{
public class MyParentClass
{
public class MyNestedClass
{
}
}
}
Now you can instantiate it somewhere else like this:
MyNamespace.MyParentClass.MyNestedClass x =
new MyNamespace.MyParentClass.MyNestedClass();
The purpose of this, like namespaces, is for organization. It's up to you as the designer whether or not you use nested classes instead of a flat class structure, but it can be convenient when you have a class whose meaning, definition, or usage is inextricably tied to the another class and doesn't have any relevance or meaning outside of that class.
For example, imagine you have a Widget class which has an ID property that's more than just a simple int or Guid...you might have a WidgetID enumeration, for example that could reside as a nested class in Widget.
To access nested classes you need to do the following:
using System;
using mynamespace.myFolder1;
namespace mynamespace.myFolder2
{
public class F2
{
// class properties...
// class methods...
void SomeMethod()
{
// no need to instantiate an object of F1 class
var f1Nest = new F1.F1_Nest();
}
}
}
The nested class F1_Nest can be accessed in class F2 as:
using System;
using mynamespace.myFolder1;
namespace mynamespace.myFolder2
{
public class F2
{
// class properties...
// class methods...
// I have to access nested class F1_Nest here...
void F2_Method()
{
F1.F1_Nest();
}
}
}
Declare the object of F1_Nest as follows
F1.F1_Nest objYourObjectVariableName=new F1.F1_Nest();
Though many questions on this topic exist, I am unable to find (yet) a satisfying solution:
Is it possible (and if yes, how?) to access a derived class from the base virtual method?
Let's imagine I have the following classes:
public class parent_class
{
public virtual string common_method () {
dynamic child = /* something to access the derived class */ ;
if (child == null)
return typeof(parent_class).FullName;
else
return child.GetType().FullName;
}
}
public class child_class1 : parent_class {}
public class child_class2 : parent_class {}
public class child_class3 : parent_class {}
Is it possible to execute the following code (and getting the correct result)?
parent_class p = new parent_class();
child_class1 c1 = new child_class1();
child_class2 c2 = new child_class2();
child_class3 c3 = new child_class3();
System.Console.WriteLine(p.common_method()); // result: 'parent_class'
System.Console.WriteLine(c1.common_method()); // result: 'child_class1'
System.Console.WriteLine(c2.common_method()); // result: 'child_class2'
System.Console.WriteLine(c3.common_method()); // result: 'child_class3'
EDIT: After reading the comments and replies I have to add the following points:
I have about 300 different "child classes", so overriding is not an option
I do not want to print the derived class' name - It was just an example
#Siamak Ferdos: I tried the this-keyword, but it somehow did not work as I intended.
Yes you can do it by 'this' keyword simply:
public class parent_class
{
public virtual string common_method()
{
//dynamic child = /* something to access the derived class */ ;
if (this.GetType() == typeof(parent_class))
return typeof(parent_class).FullName;
else
return this.GetType().FullName;
}
}
public class child_class1 : parent_class { }
public class child_class2 : parent_class { }
public class child_class3 : parent_class { }
If I understand your question correctly, you want to print the classes full name via a common base class method. At runtime, the actual instantiated type name is what GetType().FullName will produce, not the type of the base class.
This can be tested with a simple example:
void Main()
{
var parent = new Parent();
var child = new Child();
Console.WriteLine(parent.GetName());
Console.WriteLine(child.GetName());
}
public class Parent
{
public string GetName()
{
return this.GetType().FullName;
}
}
public class Child : Parent
{
}
Yields:
UserQuery+Parent
UserQuery+Child
Where UserQuery is the defined namespace.
There is no need for the method to be virtual or overriden in the derived class for this to work.
Can I create partial class in different namespaces? Will it work correct?
e.x.:
class1.cs
namespace name1
{
public partial class Foo
{
Bar1(){
return 10;
}
}
}
class2.cs
namespace name1.name2
{
public partial class Foo
{
Bar2(){
return 100;
}
}
}
main.cs
using name1;
using name1.name2;
namespace mainClass
{
public class mainClass
{
Foo classFoo = new Foo();
int Count = classFoo.Bar1() + classFoo.Bar2();
// Will Count = 110?
}
}
What should I do to make it work? (if my example not correct)
A class's name includes it's namespace, so name1.Foo and name1.name2.Foo are two completely separate types. So the short answer to your question is: No.
Why do you need to do something like this?
Partial class is only possible in same namespace and same assembly.
Namespace could be in two different assemblies but partial class could not.
Here are some point to consider while implementing the partial classes:-
Use partial keyword in each part of partial class.
Name of each part of partial class should be the same but source file name for each part of partial class can be different.
All parts of a partial class should be in the same namespace.
Each part of a partial class should be in the same assembly or DLL, in other words you can't create a partial class in source files of a different class library project.
Each part of a partial class has the same accessibility. (like private, public or protected)
If you inherit a class or interface on a partial class then it is inherited on all parts of a partial class.
If a part of a partial class is sealed then the entire class will be sealed.
If a part of partial class is abstract then the entire class will be considered an abstract class.
Partial Classes in C#
This will not work. The compiler will give you an ambiguous name error on the Foo classFoo = new Foo(); line. For partial classes to work, they must be in the same namespace because the namespace is actually part of the fully qualified name of the type.
Also, for static classes you can implement something like this with the help of fresh C# 6.0 using static feature.
Consider:
namespace SomeLogic1
{
public static class Util
{
public static int Bar1()
{
return 1;
}
}
}
namespace SomeLogic2
{
public static class Util
{
public static int Bar2()
{
return 2;
}
}
}
namespace GeneralStuff
{
using SomeLogic1;
using SomeLogic2;
public class MainClass
{
public MainClass()
{
// Error CS0104
// 'Util' is an ambiguous reference between 'SomeLogic1.Util' and 'SomeLogic2.Util'
var result = Util.Bar1() + Util.Bar2();
}
}
}
Right, that does not compile, the error message is clear. To fix the situation you can directly specify namespaces (but you don't want this as far as I understand):
namespace GeneralStuff
{
public class MainClass
{
public MainClass()
{
var result = SomeLogic1.Util.Bar1() + SomeLogic2.Util.Bar2();
}
}
}
OR you can apply using static feature this way:
namespace GeneralStuff
{
using static SomeLogic1.Util;
using static SomeLogic2.Util;
public class MainClass
{
public MainClass()
{
var result = Bar1() + Bar2();
}
}
}
Perhaps it is ok to do this for some helper/utils classes. But partial classes are not the way, as other have noticed.
Restrictions on partial classes and method from MSDN https://msdn.microsoft.com/en-us/library/wa80x488.aspx
I am assuming your main goal was to distribute the methods amongst different namespaces, otherwise it would have been trivial (put everything in one class whether partial or not and you're done).
So the assumed objectives are:
Have the 2 methods Bar1 in namespace name1 and Bar2 in namespace name1.name2
Be able to invoke any of the above methods in the context of one class, here ClsFoo
You can't achieve this with partial classes, but you can achieve it in a different way: if you use extension methods and bind them to a particular class, here ClsFoo, then you can do the following:
using SomeOtherNamespace;
using name1;
using name1.name2;
namespace mainClass
{
public static class mainClass
{
public static void Main()
{
var classFoo = new ClsFoo();
var count = classFoo.Bar1() + classFoo.Bar2();
Console.WriteLine($"count = {count}"); // output is 110
} // main
} // class
} // namespace
namespace SomeOtherNamespace
{
public class ClsFoo
{
// does not need to contain any code
} // class
} // namespace
namespace name1
{
public static class FooExt
{
public static int Bar1(this ClsFoo foo)
{
return 10;
} // method
} // class
} // namespace
namespace name1.name2
{
public static class FooExt
{
public static int Bar2(this ClsFoo foo)
{
return 100;
} // method
} // class
} // namespace
Run it online
This way, you declare an empty class ClsFoo and then write some extension methods Bar1() and Bar2(), which reside in different namespaces and static extension classes.
Note: The extension classes may have the same name FooExt as long as they are in different namespaces, of course you can also give them different names like FooExt1 and FooExt2 if you like - and the example will still work; even in older versions of C#.
I am trying to do the following in C# 4.0:
I have a Base Class and 2 derived classes
public class Base {}
public class DerivedClass1 : Base {}
public class DerivedClass2 : Base {}
I want to do something like this, but it doesn't work.
How to I tell a Generic List to accept a Base Class and the derived classes of the base class.
public class Class_1
{
public Class_1()
{
List<DerivedClass2> list = new List<DerivedClass2>();
new Class_2(list);
}
}
public class Class_2
{
public Class_2(List<Base> list)
{
}
}
In Java I can do something like this
public class Class_2
{
public Class_2(List<? extends Base> list)
{
}
}
Does something like that exists in C#
I hope my question is clear, its just about the generics of the List.
Thanks a lot in Advance :)
General case:
function Foo<T>(List<T> list) where T : Base {
...
}
plus for interfaces and delegates, C# allows co/contravariance.
For e.g. IEnumerable<T> and IList<T>, your code will therefore work! Note that if this was allowed for List<T>s, you could insert a Derived1 into a list of Derived2s by using the common base class, which would break type safety. So simply stick to the above, readonly interfaces.
I think you mean either:
// Define other methods and classes here
public class Class_1
{
public Class_1()
{
List<DerivedClass2> list = new List<DerivedClass2>();
new Class_2<DerivedClass2>(list);
}
}
public class Class_2<T> where T : Base
{
public Class_2(List<T> list)
{
}
}
Or, if you want the constructor to be generic, and not the class:
// Define other methods and classes here
public class Class_1
{
public Class_1()
{
List<DerivedClass2> list = new List<DerivedClass2>();
Class_2.Create(list);
}
}
public class Class_2
{
public static Class_2 Create<T>(List<T> list) where T : Base
{
// Stuff
return new Class_2(/*Stuff*/);
}
public Class_2()
{
}
}