CODEWITHSUNDEEP
c#ooppropertiesinterface
SoftAllan
SoftAllan

Reputation: 363

How does a C# Interface as a property work?

I am looking at the example from Using SignalR in WinForms and WPF in order to get an idea of how to implement SignalR in a .NET client application/dll. And I came across something that I don't get the concept of.

private IHubProxy HubProxy { get; set; }

When looking at the IHubProxy I can see that it is an interface. I have always understood that you could not make an instance of an interface but it was rather a contract for a new class if you implement it telling the new class what methods it has to implement.

How does an interface setup as a property work?

Upvotes: 1

Views: 100

Answers (2)

Sid
Sid

Reputation: 14896

Of course you can't make an instance for an Interface but you can make an instance of a class that implements that interface.

Let me make an example, consider the following code:

interface IEmailSender
{
   void SendEmail();
}

public class EmailSender : IEmailSender 
{
   public void SendEmail()
   {
      throw new NotImplementedException();
   }

   public void DoOtherStuff()
   {
      throw new NotImplementedException();
   }
}

Now the following code is perfectly legal:

IEmailSender mailSender = new EmailSender(); 
mailSender.SendEmail(); //Works just fine
mailSender.DoOtherStuff(); //Will raise an error at compile time

Usage in a property

Let's build a test class:

public class Test 
{
    public IEmailSender MyEmailSender;
}

Now let's check the following code: 

var testOBJ = new Test();
testOBJ.MyEmailSender = new IEmailSender(); //Raises a compile time error, as you outlined yourself
testOBJ.MyEmailSender = new EmailSender(); //Perfectly Legal

Basically you can asign to that property anything that implements that interface

Hope it's clear now :)

Upvotes: 1

Sergio Moreno
Sergio Moreno

Reputation: 1

You're right, you can't make instances of an interface.

What that code means is that the HubProxy property is of a type that inhertis the IHubProxy interface. So for example, the get returns an instance of a class that implements the IHubProxy interface.

Upvotes: 0

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