Understanding C# Interfaces & Fields and Properties

Question

Say I have an interface

interface IPets
{
      int HungerGage;

      int HungerGageEquivelentAsProperty{ get; }
}

Using the same namespace, why can I not instantiate these properties and fields like this:

class Cat : IPets
{
      int IPets.HungerGage = 100;

      int IPets.HungerGageEquivelentAsProperty = 100;
}

Or instantiate these like this:

class Cat : IPets
{
      public int HungerGage = 100;

      public int HungerGageEquivelentAsProperty = 100;
}

I've been getting errors so much with these that obviously I don't understand. I've used the keyword override plenty as well, and it doesn't seem to work consistently for me either. I've seen the int IInterface.field = variable in the microsoft documentation, but it seems that my C# instructor here was able to flawlessly use public int field = variable. For me, neither work, so help would be appreciated! Thanks

Answer 1 · 2020-10-16T03:18:48Z

October 16, 2020 3:18am

You might care to provide links to the treehouse video and to the microsoft documentation (and maybe code snippets). I'm not really a c# expert, but I think microsoft says that you can't provide fields on an interface ("An interface may not declare instance data such as fields, auto-implemented properties, or property-like events."). It sounds like there might be an ability to use static fields but it sounds like it might be newish. I tried running a quick demo in workspace and whatever version of c# they use (I'd assume probably a little older), it won't let me define fields and I have to provide implementation for properties to get it to compile. For reference, my demo code was:

using System;

class MainClass {
  public static void Main (string[] args) {
    IPet fido = new Dog();
  }
}

interface IPet
{
      int HungerGageEquivelentAsProperty{ get; }

      int SomethingElse { get; set; }
}

class Dog : IPet {
    //won't compile if i don't provide implementation.
    public int HungerGageEquivelentAsProperty{ get; } = 200;

    public int SomethingElse { get; set; }

    public Dog()
    {
      SomethingElse = 100;
    }

}

it seems to at least let me use properties with an implicit syntax. If that's all you need, then maybe that gets you by for now.

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Evan Welch

Evan Welch

Understanding C# Interfaces & Fields and Properties

1 Answer

Simon Coates

Simon Coates