inherit from two classes in C#

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Possible Duplicate:
Multiple Inheritance in C#

I have two classes Class A and Class B. These two classes cannot inherit each other. I am creating new class called Class C. Now, I want to implement the methods in class A and class B by inheriting. I am aware that multiple inheritance is not possible in C# but is there any other way to do this?

You should probably be using an interface... http://stackoverflow.com/questions/178333/multiple-inheritance-in-c-sharp — Oofpez, Jun 21 '12 at 09:05

score 63 · Accepted Answer · edited Jun 21 '12 at 09:14

Multitiple inheritance is not possible in C#, however it can be simulated using interfaces, see Simulated Multiple Inheritance Pattern for C#.

The basic idea is to define an interface for the members on class B that you wish to access (call it IB), and then have C inherit from A and implement IB by internally storing an instance of B, for example:

class C : A, IB
{
    private B _b = new B();

    // IB members
    public void SomeMethod()
    {
        _b.SomeMethod();
    }
}

There are also a couple of other alternaitve patterns explained on that page.

score 20 · Answer 2 · edited May 24 '23 at 19:18

A common alternative to inheritance is delegation (also called composition): X "has a" Y rather than X "is a" Y. So if class A has functionality for dealing with Foos, class B has functionality for dealing with Bars, and you want both in class C, then you can do something like this:

public class A() {
  private FooManager fooManager = new FooManager(); // (or inject, if you have IoC)

  public void handleFoo(Foo foo) {
    fooManager.handleFoo(foo);
  }
}

public class B() {
  private BarManager barManager = new BarManager(); // (or inject, if you have IoC)

  public void handleBar(Bar bar) {
    barManager.handleBar(bar);
  }
}

public class C() {
  private FooManager fooManager = new FooManager(); // (or inject, if you have IoC)
  private BarManager barManager = new BarManager(); // (or inject, if you have IoC)

  // ... etc.
}

score 13 · Answer 3 · answered Jun 21 '12 at 09:13

If you want to literally use the method code from A and B you can make your C class contain an instance of each. If you code against interfaces for A and B then your clients don't need to know you're giving them a C rather than an A or a B.

interface IA { void SomeMethodOnA(); }
interface IB { void SomeMethodOnB(); }
class A : IA { void SomeMethodOnA() { /* do something */ } }
class B : IB { void SomeMethodOnB() { /* do something */ } }
class C : IA, IB
{
    private IA a = new A();
    private IB b = new B();
    void SomeMethodOnA() { a.SomeMethodOnA(); }
    void SomeMethodOnB() { b.SomeMethodOnB(); }
}

score 9 · Answer 4 · answered Jun 21 '12 at 09:09

Use composition:

class ClassC
{
    public ClassA A { get; set; }
    public ClassB B { get; set; }   

    public C (ClassA  a, ClassB  b)
    {
        this.A = a;
        this.B = b;
    }
}

Then you can call C.A.DoA(). You also can change the properties to an interface or abstract class, like public InterfaceA A or public AbstractClassA A.

score 6 · Answer 5 · answered Jun 21 '12 at 09:14

Make two interfaces IA and IB:

public interface IA
{
    public void methodA(int value);
}

public interface IB
{
    public void methodB(int value);
}

Next make A implement IA and B implement IB.

public class A : IA
{
    public int fooA { get; set; }
    public void methodA(int value) { fooA = value; }
}

public class B : IB
{
    public int fooB { get; set; }
    public void methodB(int value) { fooB = value; }
}

Then implement your C class as follows:

public class C : IA, IB
{
    private A _a;
    private B _b;

    public C(A _a, B _b)
    {
        this._a = _a;
        this._b = _b;
    }

    public void methodA(int value) { _a.methodA(value); }
    public void methodB(int value) { _b.methodB(value); }
}

Generally this is a poor design overall because you can have both A and B implement a method with the same name and variable types such as foo(int bar) and you will need to decide how to implement it, or if you just call foo(bar) on both _a and _b. As suggested elsewhere you should consider a .A and .B properties instead of combining the two classes.

`public ` is not a valid keyword for interface member definitions ;-) — Stefan, Aug 05 '19 at 22:05

score 3 · Answer 6 · answered Jun 21 '12 at 09:04

3

You can define a base class for A and B where you can hold a common methods/properties/fields of those.

After implement C:Base.

Or in order to simulate multiple inheritance, define a common interface(s) and implement them in C

Hope this helps.

answered Jun 21 '12 at 09:04

Tigran

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If i use interface then I need to define the methods in Class C. Is there any other way where I can directly call the methods? – Virus Jun 21 '12 at 09:06
@Virus: you don't need to define **all** methods, but only those you want to *share* between different types. – Tigran Jun 21 '12 at 09:08

score -5 · Answer 7 · answered Jun 21 '12 at 09:18

Do you mean you want Class C to be the base class for A & B in that case.

public abstract class C
{
    public abstract void Method1();

    public abstract void Method2();
}

public class A : C
{
    public override void Method1()
    {
        throw new NotImplementedException();
    }

    public override void Method2()
    {
        throw new NotImplementedException();
    }
}


public class B : C
{
    public override void Method1()
    {
        throw new NotImplementedException();
    }

    public override void Method2()
    {
        throw new NotImplementedException();
    }
}

This is not an answer to the question – Nick Gallimore Jun 22 '18 at 18:59 — Nick Gallimore, Jun 22 '18 at 18:59

inherit from two classes in C#

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