How do I create an instance of a public interface

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Here is a code sample: I don't want to expose the internal sealed class just the interface.

here is what I want to do IDataService id = new IDataService() is it possible or is there a work around?

C#

public interface IDataService
{
    method a
    method b
    method c
    method etc
}

internal sealed class DataService : IDataService
{
    method a
    method b
    method c
    method etc
}

thanks

What I have tried:

The only thing I have tried that works is to change the class to public but that is not an option for me

Posted 10-Aug-17 6:37am

Member 13354128

Updated 10-Aug-17 6:52am

Kornfeld Eliyahu Peter

v2

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Kornfeld Eliyahu Peter · Answer 1 · 2017-08-10T06:45:00

Solution 1

There is no way to create an object from an interface!
I'm not sure what do you mean by not exposing the class, but your only option is:

C#

IDataService id = new DataService()

Posted 10-Aug-17 6:45am

Kornfeld Eliyahu Peter

Updated 10-Aug-17 6:46am

v2

cvogt61457 · Answer 2 · 2017-08-10T06:48:00

Solution 2

You can't create an instance of an interface.
You define a class which implements the interface. Then create an instance of that class.

// This works
IDataService myService = new DataService();

Posted 10-Aug-17 6:48am

cvogt61457

Comments

Member 13354128 11-Aug-17 11:51am

Thanks for the input and this works as long as I make the DataService public but I need it to stay internal To prevent developers from accessing the internal classes and trying to alter them by extending them or deriving off of them. Is there a workaround/back door?

This--> internal sealed class DataService : IDataService
NOT This--> public sealed class DataService : IDataService

cvogt61457 11-Aug-17 13:24pm

Internal is available within an assembly. It is not visible outside the assembly.
You will need to provide a class (a factory) within the assembly that will give you the IDataService to use outside the assembly.

Assembly1
public interface IDataService
{
}
internal sealed class DataService : IDataService
{
}

Assembly2
// Won't work - DataService is internal
DataService dataService = new DataService();

// Will work
IDataService dataService = factory.GetService();

Kornfeld Eliyahu Peter 12-Aug-17 15:58pm

The moment your class is sealed no other class can inherit from it, public is irrelevant to that...
If you want to prevent from others to see your code - do some obfuscation...

Richard MacCutchan · Answer 3 · 2017-08-10T06:52:00

Solution 3

You have to follow the rules: Interfaces (C# Programming Guide) | Microsoft Docs[^],
Especially:

Quote:
To implement an interface member, the corresponding member of the implementing class must be public, non-static, and have the same name and signature as the interface member.

Posted 10-Aug-17 6:52am

Richard MacCutchan