What would cause a property get on an interface to fail?

Question

I have an interface with a property, and a class that implements that interface. I cast an instance of the class to the interface, then attempt to read the property and it doesn't retrieve the value. Can anyone see why?

Interface:

public interface IFoo
{
    int ObjectId { get; }
}

Class:

public class Bar : IFoo
{
     public int ObjectId { get; set; }
}

Usage:

...
Bar myBar = new Bar() { ObjectId = 5 };
IFoo myFoo = myBar as IFoo;
int myId = myFoo.ObjectId;  //Value of myFoo.ObjectId is 5 in Watch, but myId remains at 0 after statement
...

This is oversimplified, but essentially what I'm doing. Why can I see the value of myFoo.ObjectId in the watch window, but the assignment to myId fails (value is 0 before and after assignment)?

Answer 1

You might have manipulated the data on your watch through manual intervention or a statement that changed the value.

I did a quick test on your code in a Console Application and the value of myId is 5.

class Program
{
    static void Main(string[] args)
    {
        Bar myBar = new Bar() { ObjectId = 5 };
        IFoo myFoo = myBar as IFoo;
        int myId = myFoo.ObjectId;

        Console.WriteLine(myId); // 5

        Console.ReadLine();
    }
}

interface IFoo
{
    int ObjectId { get; }
}

class Bar : IFoo
{
    public int ObjectId { get; set; }
}