C# : interface : same method in 2 interfaces

Question

I have 2 interfaces as,

    public interface I1
    {
       string GetRandomString();
    }

   public interface I2
   {
      string GetRandomString();
   }

and in a class, I have implanted both,

    public class ClassA : I1, I2
    {

      string I1.GetRandomString()
      {
         return "GetReport I1";
      }

      string I2.GetRandomString()
      {
          return "GetReport I1";
       }

    }

Now in main method I want to access , these interface method but not able to

    static void Main(string[] args)
    {
        var objClassA = new ClassA();
        objClassA.GetRandomString(); // not able to do this, comile time error ... 
    }

I know that , I am missing some basic OOPS stuff , just wanted to know that. any Help ?

supercat · Accepted Answer · 2011-07-12 17:44:22Z

If you will sometimes be wanting to use one interface and sometimes the other, it will likely be necessary to use a cast for at last one of them. If you control the type and can have one of the interface functions be available directly rather than as an explicit implementation, that will avoid the requirement for casting on that one. To avoid having to typecast either function, you should make them available under separate names within the object. Because in C# any method implementing anyInterface.Boz must be called Boz, the best bet approach is probably to have the implementations of IFoo.Boz and IBar.Boz simply call public methods called FooBoz and BarBoz, which could then be called "directly" without ambiguity.

Although casting to interfaces is inexpensive with classes, it can be expensive with structures. This cost may in some cases be avoided by using static methods like the following:

    public interface AliceFoo { void foo();};
    public interface BobFoo { void foo();};
    static void do_alice_foo<T>(ref T it) where T:AliceFoo
    {
        it.foo();
    }
    static void do_bob_foo<T>(ref T it) where T : BobFoo
    {
        it.foo();
    }

This approach allows either 'foo' method to be used without having to typecast anything.

Petar Ivanov · Accepted Answer · 2011-07-10 05:49:58Z

5

The problem is that these functions are not member functions of MyClass, because they are defined and I1.GetRandomString as I2.GetRandomString. You can only call them on one of the interfaces:

    I1 objClassA = new ClassA();
    objClassA.GetRandomString();

or

    I2 objClassA = new ClassA();
    objClassA.GetRandomString();

answered Jul 10, 2011 at 5:49

Petar Ivanov

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Comments

tkerwood · Accepted Answer · 2011-07-10 05:52:44Z

4

You can cast the object to the type of interface that you require and then call the method.

if (objClassA is I1)
{
    ((I1)objClassA).GetRandomString();
}
if (objClassA is I2)
{
    ((I2)objClassA).GetRandomString();
}

answered Jul 10, 2011 at 5:52

tkerwood

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Comments

oxilumin · Accepted Answer · 2011-07-10 05:49:31Z

2

You should cast your object to particular interface type.

static void Main(string[] args)
{
    var objClassA = new ClassA();

    I1 objClassAThreatedAsI1Interface = (I1)objClassA;
    objClassAThreatedAsI1Interface.GetRandomString();

    I2 objClassAThreatedAsI2Interface = (I2)objClassA;
    objClassAThreatedAsI2Interface.GetRandomString();
}

answered Jul 10, 2011 at 5:49

oxilumin

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Comments

Jeff Mercado · Accepted Answer · 2011-07-10 05:57:22Z

You've explicitly implemented the interfaces. So the method implementations belong to the interfaces, not the type you defined. As far as the compiler is concerned, the method does not exist for that type.

You need to explicitly cast your instance to the interface you want to call and call the method (as the others have shown).

Or better, choose one of the interfaces as the "main" interface and leave out the explicit implementation.

i.e.,

public class ClassA : I1, I2
{
    // make I1's implementation the "main" one
    public string GetRandomString()
    {
        return "GetReport I1";
    }

    // I2's implementation could only be called via a reference to an I2
    string I2.GetRandomString()
    {
        return "GetReport I2";
    }

}

Alternatively, just use a single implementation of the method (and leave out the explicit implementations).

Chris Catignani · Accepted Answer · 2024-04-01 14:19:27Z

1

If you need to call the GetRandomString() method from a specific interface, you can explicitly cast the instance to the desired interface type:

ClassA myClass = new ClassA ();
((I1)myClass).GetRandomString(); // Calls CommonMethod from I1
((I2)myClass).GetRandomString(); // Calls CommonMethod from I2

edited Apr 1, 2024 at 14:19

Chris Catignani

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answered Apr 1, 2024 at 10:39

tim neet

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Comments

Tim · Accepted Answer · 2011-07-10 05:49:32Z

0

Mark your two GetRandomString methods as public in ClassA. If you don't provide an access modifier, it defaults to private.

answered Jul 10, 2011 at 5:49

Tim

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2 Comments

oxilumin Over a year ago

You can't use access modifiers for explicit interface implementation. And it's impossible to use implicit implementation for two different interfaces with same-signature methods, otherwise the same implementation will be used for both interfaces.

mrydengren Over a year ago

Explicit interface declarations cannot be made public.

Paul Hadfield · Accepted Answer · 2011-07-10 05:56:16Z

0

You need to cast your object to the interface that defines the version of the method that you wish to call.

If you just want a single version of the method to be defined in your class, remove the explicit definition of the interface (in other words, remove the I1. from the first definition of the function and entire I2.* method entirely)

edited Jul 10, 2011 at 5:56

answered Jul 10, 2011 at 5:50

Paul Hadfield

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Comments

Wai Ha Lee · Accepted Answer · 2021-11-19 11:10:52Z

0

using System;
namespace demo
{
    public interface I1
    {
        string GetRandomString();
    }

    public interface I2
    {
        string GetRandomString();
    }
    public class ClassA : I1, I2
    {
        
        public string GetRandomString()
        {
            return "GetReport I1";
        }

        
        string I2.GetRandomString()
        {
            return "GetReport I2";
        }
        public static void Main()
        {
            I1 objClassA = new ClassA();
            objClassA.GetRandomString();
           //I2 objClassA = new ClassA();
           // objClassA.GetRandomString();
        }

    }
}

edited Nov 19, 2021 at 11:10

Wai Ha Lee

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answered Nov 19, 2021 at 5:25

kundan kumar jha

1

2 Comments

ZF007 Over a year ago

Add context to improve answer quality. Keep in mind there are more solutions and you might want to attract them to yours more than others ;-) End of Review.

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

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