I implemented 2 classes:
public class A
{
public string GetName()
{
return "Class A";
}
}
public class B
{
public string GetName()
{
return "Class B";
}
}
I also created an interface that is not been assign to class A and B:
public interface TellMyNameInterface
{
string GetName();
}
I want to use the interface with class A and B:
TellMyNameInterface a = new A();
TellMyNameInterface b = new B();
string aName= a.GetName();
Is there any way to use an instance of class A or B with that interface without declaring it in the class declaration?
You cannot, but you can write adapter classes to make it more convenient to do the conversions, and then use extension methods to make creating the adapter classes look more natural (and in fact hide the adapter classes behind the interface).
You would normally only do this if you are unable to change the original class definitions to implement the required interface directly.
So given these classes that you cannot edit:
public class A
{
public string GetName()
{
return "Class A";
}
}
public class B
{
public string GetName()
{
return "Class B";
}
}
And this interface that you really want them to implement, but can't:
public interface ITellMyNameInterface
{
string GetName();
}
You can write a couple of adapter classes that do implement the interface, like this:
public class AAdapter: ITellMyNameInterface
{
public AAdapter(A a)
{
_a = a;
}
public string GetName()
{
return _a.GetName();
}
private readonly A _a;
}
public class BAdapter: ITellMyNameInterface
{
public BAdapter(B b)
{
_b = b;
}
public string GetName()
{
return _b.GetName();
}
private readonly B _b;
}
Then write extension methods to make it more natural to create the adapter classes:
public static class ABExt
{
public static ITellMyNameInterface AsITellMyNameInterface(this A self)
{
return new AAdapter(self);
}
public static ITellMyNameInterface AsITellMyNameInterface(this B self)
{
return new BAdapter(self);
}
}
Once you've done all that, it does at least make it simpler to get the ITellMyNameInterface for an instance of A or B, like so:
ITellMyNameInterface a = new A().AsITellMyNameInterface();
ITellMyNameInterface b = new B().AsITellMyNameInterface();
No you can not. The only way i can see is using object to store it and then call the functions via reflection.
Related
I have 2 APIs which both have the same methods but with different names.
I made an abstract class inherited from this with both of them.
Now I am trying to make another class which uses those APIs and I don't want it to care which API it uses.
How do I pass the abstract class as a parameter and use it as one of the api's?
Is there a better way to do it?
Example Code :
public abstract class AbstractClass
{
public abstract string Func1();
}
public class Class1: AbstractClass
{
public override string Func1()
{
return "Class1";
}
}
public abstract class Class2: AbstractClass
{
public override string Func1()
{
return "Class2";
}
}
public class Class3
{
Type type;
public Class3(Type type)
{
this.type = type;
}
public string UseFunc1()
{
//I know this wont work but what shuld I do
type a = new type();
return a.Func1();
}
}
I think what you might be trying to achieve is the below. While you can't create an abstract class you can pass one
public class Class3
{
AbstractClass abstractMember
public Class3(AbstractClass abstractMember)
{
this.abstractMember = abstractMember;
}
public string UseFunc1()
{
return abstractMember.Func1();
}
}
You'd call it like:
Class2 c2 = new Class2();
Class3 c3 = new Class3(c2);
I have a class A, and a class AStore. My requirement is to prevent all other methods from initializing an instance of class A, which they should get an instance from AStore. In addition, I also need to access the member functions of A from the instance.
Factory pattern is not suitable for this problem as the constructor of A is still public. Ideally, it should throw compilation error when calling the constructor of class A while having access to its member functions.
Can I get C# solutions to this?
For restricting others to create an instance of class A you can use a private constructor and a static factory method to get the instance of that class.
public class A
{
private A(){}
public static A GetInstance()
{
return new A();
}
public void MemberFunctionOfA()
{
// blah blah...
}
}
To enforce instance creation of A only via Astore you can use protected modifier and derive AStore from A. That way, only AStore will have access to its protected members like 'constructor' or 'factory method':
public class Astore : A
{
public A GetInstanceOfA()
{
return base.GetInstance();
}
}
public class A
{
protected A() { }
protected A GetInstance()
{
return new A();
}
public void MemberFunctionOfA()
{
// blah blah...
}
}
//Usage
public class ConsumerClass
{
public void Test()
{
var a = new A(); // Compile error
a = new Astore().GetInstanceOfA();
a.MemberFunctionOfA();
}
}
But there're still chances that another class say 'UnWantedStore' can derive from A and serve instance of A.
Another approach is moving AStore and A classes to the dedicated project and make constructor of A class internal.
// Project A
namespace ProjectA
{
public class A
{
public int PropertyOne { get; set; }
public string PropertyTwo { get; set; }
internal A() {}
}
public class AStore
{
public A CreateA()
{
//internal constructor can be used
return A();
}
}
}
// Project ConsumerOfA
namespace ConsumerOfA
{
public static void UseA()
{
var store = new AStore();
var instanceOfA = store.CreateA();
// have access to the A's public members
}
}
With this approach you will get perfect encapsulation you trying to achive.
Abstract classes to the rescue!
Indeed, there's yet another possible approach! I've never used it but it might work in your scenario. See the following code sample:
public abstract class A
{
public string Text { get; set; }
public string SayHello() => "hello world!";
}
public class AStore
{
private class AInternal : A {}
public void DoStuff()
{
A a = new AInternal();
a.Text = "whatever";
string helloText = a.SayHello();
}
}
Let's explain the approach:
Class A is abstract, therefore it can't be instantiated.
Class AStore implements a private nested class called AInternal which just inherits A to let AStore members be able to instantiate A. Since AInternal is private, no other class than AStore can instantiate AInternal!
Class AStore can access public A members because AInternal inherits A!
You can do this with reflection too:
public class ClassA
{
// The constructor(s) have to be private
private ClassA() { }
// Whatever other code you want
}
public class ClassB
{
public static ClassA GetClassAInstance()
{
// Use reflection to get the private default constructor
ConstructorInfo constructor = typeof(ClassA).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, new Type[] { }, null);
ClassA instance = constructor.Invoke(new object[] { }) as ClassA;
return instance;
}
}
You can find more information on the GetConstructor method here.
Is there a way to have a generic field in a class to specialize to a specific type in the constructor?
For example:
class concreteClass1
{
private int a;
public concreteClass1( int a)
{
this.a = a;
}
}
class concreteClass2
{
string b;
public concreteClass2(string b)
{
this.b = b;
}
}
class A<T>
{
private T field;
public A(int x)
{
field = new concreteClass1(x); //error here CS0029
}
public A(string y)
{
field = new concreteClass2(y); //error here CS0029
}
}
So T can be either concreteClass1 or concreteClass1 and their respective ctors will have different signatures.
I would refactor this to use dependency injection. That way the class doesn't contain code to create other classes that it depends on, like myConcreteField = new ConcreteA<T>(4);. Dependency injection is used to keep code from getting tied into difficult knots like this.
(Your example is very, very abstract, which makes it a little difficult. If you use class names like "Concrete" and "Implementation" then it makes the answer harder to read because we use those same words to describe concepts.)
Instead, whatever that Concrete thing is, declare an interface, like
public interface ISomethingThatTheOtherClassNeeds<T>
{
public int MySomething {get;set;}
}
public class SomethingThatTheOtherClassNeeds : ISomethingThatTheOtherClassNeeds<string>
{
public int MySomething {get;set;}
}
Then in your Implementation class:
class Implementation<T>
{
private readonly ISomethingThatTheOtherClassNeeds<T> _something;
public Implementation(ISomethingThatTheOtherClassNeeds<T> something)
{
_something = something;
}
void DoSomething()
{
Console.Write(_something.MySomething.ToString());
}
}
The difference is that instead of being responsible for creating whatever that class is, it's passed to Implementation in the constructor. Implementation doesn't even know what the class is - it just knows that it matches the interface.
This is especially helpful if those other classes in turn depend on more classes. If you're creating them by calling new in your class then that class has to know how to create those classes.
Then to wire it up you would use a dependency injection container like Windsor, Unity, Autofac, and many more. That's not very commonly done with console applications, but I'm guessing this is more experimental than real.
Well this was a bit tricky due to having to convert types. Maybe this will work for you?
class Program
{
static void Main(string[] args)
{
var myImplementation = new Implementation<int>(4);
var myImplementation2 = new Implementation<string>("Hello World");
Console.WriteLine(myImplementation.myConcreteField); // outputs 4!
Console.WriteLine(myImplementation2.myConcreteField); // outputs Hello World
}
}
abstract class MyAbstract<T>
{
public T MySomething;
public MyAbstract(T something)
{
MySomething = something;
}
}
class ConcreteA<T> : MyAbstract<T>
{
public ConcreteA(int something) : base((T)Convert.ChangeType(something, typeof(T)))
{
}
}
class ConcreteB<T> : MyAbstract<T>
{
public ConcreteB(string something) : base((T)Convert.ChangeType(something, typeof(T)))
{
}
}
class Implementation<T>
{
public MyAbstract<T> myConcreteField;
public Implementation(T a)
{
myConcreteField = new ConcreteA<T>(4);
}
void DoSomething()
{
Console.Write(myConcreteField.MySomething.ToString());
}
}
QUESTION IS CLARIFIED
new thread : subclass properties accessed in generic method with superclass input
I have a base class A
subClasses B, C, and D inherit from A.
Each subClass has 3 subClasses a, b, and c.
a, b, and c have a list of unique properties.
However, now I want to build a generic function to access those properties, so how would I do this without switching on Type?
Clarification : I do not want a : B to have abstract C methods/properties
Example:
public void Method(A a){
if(a.isSubClassOf(B))
{Console.WriteLine(a.BaProperty);}
if(a.isSubClassOf(C))
{Console.WriteLine(a.CbProperty);}
if(a.isSubClassOf(D))
{Console.WriteLine(a.DcProperty);}
}
You can't define a member in derived class and access it via the reference to base class without casting to derived class:
class A {}
class B
{
public int i;
}
A a = new B();
a.i = 0; // error
((B)a).i = 0; // OK
Either declare virtual property in any of base types in your hierarchy, or use casting to the concrete derived type. Of course, in the second case your method doesn't make any sense.
Typically, you would use a virtual or abstract method defined in A and overridden in the subclasses.
public abstract class A
{
protected abstract PropertyType PropertyValue {get;}
public void Method()
{
Console.WriteLine(PropertyValue);
}
}
public class B : A
{
protected override PropertyType Property { get { return PropertyType.B; } }
}
// etc...
An elegant solution is to override ToString
public abstract class A { }
public class B : A {
public int b { get; set; }
public override string ToString()
{
return b.ToString();
}
}
// Do the same with C and D ....
A[] array = new A[] { new B(), new C(), new D() };
foreach (A a in array) {
Console.WriteLine(a);
}
Note that Console.WriteLine does not need to know about a special method or property in A. It also works for types not deriving from A.
It depends greatly in what you really want to achieve. In some cases what Steve Czetty suggests is the best option.
In others you could just keep all the properties different and have a virtual method in the base class that returns for example in this case a "string" that you can then write in the console or anything you wish.
Edit: You could override ToString as Olivier suggested. But only if you feel what yo are going to retun is the "String representation of the object".
public abstract class A
{
public string PropertyA { get; set; }
public virtual string GetString() //
{
return PropertyA;
}
}
public class B:A
{
public string PropertyB { get; set; }
public override string GetString()
{
return PropertyB;
}
}
public class C:A
{
public string PropertyC { get; set; }
public override string GetString()
{
return string.Format("{0} - {1}", base.GetString(), PropertyC) // for example if you wanted to do something more complex
}
}
Now if what you need can not be solved like this, you could cast as Dennis Suggested.
There is another posibility: you could use the visitor pattern. Here you can find several ways to implement it.
Just so you have an idea you would wind up having a class similar to this: (it will depend on what you really want to achieve)
You have to implement some other basic things (interface and some methods), but from a Reference to the base class you will be able to call the corresponding "Visit" method easily. There is a lot of detail in the link i added.
class ClassicVisitor : IAVisitor
{
public string SuperComplexStringResult { get;set; }
public void Visit(B b) { SuperComplexStringResult = String.Format("Super Complex Stuff + {0}", b.PropertyB); }
public void Visit(C c) { SuperComplexStringResult = String.Format("Super Complex Stuff + {0}", c.PropertyC); }
}
I have the following situation:
public interface IStuffer
{
public string Foo { get; }
}
public class BaseClass
{
public static string Foo { get { ... } }
}
public class MyClass : BaseClass, IStuffer
{
}
This won't build because MyClass needs a Foo member. How can I use BaseClass's Foo implementation to satisfy MyClass's requirement for Foo?
It's because Foo is a static member of the BaseClass. Just take away the static keyword!
public class BaseClass
{
public string Foo { get { ... } }
}
Edit: Else if you really want it to stay static, you could use an explicit implementation
public class MyClass : BaseClass, IStuffer
{
string IStuffer.Foo { get { return BaseClass.Foo; } }
}
The problem is that your interface expects a NON-static "string Foo", if you make Foo Non-Static in BaseClass then it will satisfy your Interface :)
Good Luck
Interfaces cannot support static properties or methods. If you have an interface, all methods of that interface must be instance rather than class scope.
In two ways:
1. Rename Foo to something else and add a method Foo like this:
public class BaseClass
{
public static string FormerlyCalledFoo { get { ... } }
public string Foo { get { ... } }
}
2. If you absolutely must have a static Foo property then you can implement the IStuffer interface as an explicit interface implementation like this:
public class BaseClass : IStuffer
{
public static string Foo { get { ... } }
string IStuffer.Foo { get { ... } }
}
If using the latter method, then you have to be aware that you have to cast instances of BaseClass to IStuffer to access the IStuffer.Foo property