C# Interface with multiple functions defined

Question

Can some one help me understand why this doesn't work:

public interface IInterface
{
    string GetString(string start);
    void DoSomething();
}

public class InterfaceImpl : IInterface
{
    string IInterface.GetString(string start)
    {
        return start + " okay.";
    }
    void IInterface.DoSomething()
    {
        Console.WriteLine(this.GetString("Go")); // <-- Error: InterfaceImpl does not contain a definition for GetString
    }
}

I can't figure out why I can't call a function that is most certainly defined in the implementation.

Thanks for your help.

Consider also reading interfaces overview on MSDN - you may not need explicit implementation as cruellays' answer points out. — Alexei Levenkov
– Alexei Levenkov, Commented Jul 23, 2014 at 1:34

Community · Accepted Answer · 2017-05-23 12:21:26Z

5

Explicitly implemented methods need to be called on variable of interface type, usually with cast:

   Console.WriteLine(((IInterface)this).GetString("Go"));

More variants of calling explicitly defined methods are covered in How to call explicit interface implementation methods internally without explicit casting?

edited May 23, 2017 at 12:21

CommunityBot

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answered Jul 23, 2014 at 1:24

Alexei Levenkov

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Comments

Yuan Shing Kong · Accepted Answer · 2014-07-23 02:30:44Z

5

you do not need to explicitly specify the Interface with the method. Since InterfaceImpl is already implementing IInterface, you just need to do as follows:

public class InterfaceImpl : IInterface
{
    public string GetString(string start)
    {
        return start + " okay.";
    }
    public void DoSomething()
    {
        Console.WriteLine(GetString("Go"));
    }
}

Updated as per comment.

edited Jul 23, 2014 at 2:30

answered Jul 23, 2014 at 1:29

Yuan Shing Kong

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1 Comment

Kyle Over a year ago

Those methods should be marked public, otherwise this doesn't implement the interface.

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