how to implement interface property?

Question

Below is my interface:

public interface IBaseService
{
    List<ExceptionPairs> Exceptions { get; set; }
}

Another interface is inheriting it:

public interface IClassStudentsService: IBaseService
{

}

I have implemented this interface in below class:

public class CSService : IClassStudentsService
{
    public List<ExceptionPairs> Exceptions
    {
        get;set;
    }
}

I have created a object of CSService and tried to access List 'Exceptions' but receiving error " Object reference not set to an instance of an object. "

Can you please guide what I need to do instantiate it ?

Answer 1

Exceptions is an auto-property for an object, and as such it has not been initialized before you are accessing it.

In the constructor, initialize the property with a new list:

public class CSService : IClassStudentsService
{
    public CSService() {
         Exceptions = new List<ExceptionPairs>();
    }

    public List<ExceptionPairs> Exceptions { get; set; }
}

Answer 2

You need to add a constructor for your CSService class:

public CSService()
{
    Exceptions = new List<ExceptionPairs>();
}

In the constructor, you initialize the list.