I have a few interfaces that are

public interface ISaleOrderManager
{
    Task<IOrderDto> CreateAsync(ICreateOrderDto request);
}

public interface ICreateOrderDto
{
    long? ContactId { get; set; }
    DateTime OrderDate { get; set; }
    double TotalAmount { get; set; }
}

public interface IOrderDto:ICreateOrderDto,IEntityDto
{ }

public interface IEntityDto
{
    long Id {get;set;}
    bool isDeleted {get; set;}
}

also, I have some DTOs as well that are

public class CreateSaleOrderDto: ICreateOrderDto
{
   public long? ContactId { get; set; }
   public DateTime OrderDate { get; set; }
   public double TotalAmount { get; set; }
}

public class SaleOrderDto : IOrderDto
{
    public long Id {get;set;}
    public bool isDeleted {get; set;}
    public long? ContactId { get; set; }
    public DateTime OrderDate { get; set; }
    public double TotalAmount { get; set; }
}

And I implement ISaleOrderManager on a class that is

public class SaleOrderManager: ISaleOrderManager    
{
    public SaleOrderManager(IRepository<SaleOrder, long> entityRepository)
    {
    }

    public async Task<SaleOrderDto> CreateAsync(CreateSaleOrderDto request)
    {
        var entity = ObjectMapper<SaleOrder>(request);

        entity.Id = await _entityRepository.InsertAndGetIdAsync(entity);

        return ObjectMapper.Map<SaleOrderDto>(entity);


    }
}

So as my code depicts that I have implemented ICreateOrderDto through CreateSaleOrderDto and IOrderDto through SaleOrderDto but I'm still getting an error of "Interface Member is not implemented."

Why do I receive this error and how can I overcome it?

CodePudding user response：

You didn't implement the Task<IOrderDto> CreateAsync(ICreateOrderDto request) method in the SaleOrderManager class. You made the CreateAsync method return a Task<SaleOrderDto> instead of a Task<IOrderDto>. Also you used a parameter of type CreateSaleOrderDto instead of ICreateOrderDto.

CodePudding user response：

This is the declaration of the method

Task<IOrderDto> CreateAsync(ICreateOrderDto request);

and this is the attempt for the implementation

    public async Task<SaleOrderDto> CreateAsync(CreateSaleOrderDto request)
    {
        var entity = ObjectMapper<SaleOrder>(request);

        entity.Id = await _entityRepository.InsertAndGetIdAsync(entity);

        return ObjectMapper.Map<SaleOrderDto>(entity);


    }

I perfectly know that SaleOrderDto implements IOrderDto and that CreateSaleOrderDto implements ICreateOrderDto, but this does not qualify as an implementation of the method in the interface.

In order to understand the problem, let's consider the possibility that some other class, that may be different from CreateSaleOrderDto may also implement ICreateOrderDto. If I declare a variable to be an ISaleOrderManager and I instantiate this other class, let's call it MyCustomCreateSaleOrderDto and pass it to CreateAsync, then I justifiably expect your method to work, but it will not work, because your method mistakenly assumed the following:

1. It assumed that each and every iCreateOrderDto is a CreateSaleOrderDto
2. It assumed that each and every IOrderDto is a SaleOrderDto

You should aim to write your code in an as abstract manner as possible, so, you should aim to implement your method in a way that it expects a parameter specified as an interface and its return type should also be corresponding to the one specified by the interface, even though they are actual objects at runtime.