带接口的工厂模式，如何避免转换

Question

我尝试使用接口实现工厂模式以创建不同类型的响应，但我不知道我做的是否正确。当我用工厂 class 调用我的方法 SetExceptionResponse 时，我必须强制转换它。

接口：

public interface IResponse
    {
        int ErrorCode { get; set; }

        HeaderResponse HeaderResponse { get; set; }

        IResponse SetExceptionResponse(int code, string title, string[] errors);
    }

主要 class :

    public class Response : IResponse 
    {
        public int ErrorCode { get ; set ; }

        public HeaderResponse HeaderResponse { get; set; } = null;

        public virtual IResponse SetExceptionResponse(int code, string title, string[] errors)
        {
            HeaderResponse headerResponse = new HeaderResponse();
            if (errors.Length > 0)
            {
                foreach (string item in errors)
                    headerResponse.ErrorList.Add(item);
            }
            headerResponse.Title = title;
            headerResponse.StatusCode = code;

            return new Response
            {
                ErrorCode = code,
                HeaderResponse = headerResponse
            };
        }
    }

继承主class的其他class:

public class DeleteShipmentResponse : Response
    {
        public string Value { get; set; }

        public override string ToString()
        {
            return JsonConvert.SerializeObject(this);
        }

        public override IResponse SetExceptionResponse(int code, string title, string[] errors)
        {
            HeaderResponse headerResponse = new HeaderResponse();
            if (errors.Length > 0)
            {
                foreach (string item in errors)
                    headerResponse.ErrorList.Add(item);
            }
            headerResponse.Title = title;
            headerResponse.StatusCode = code;

            return new DeleteShipmentResponse
            {
                ErrorCode = code,
                HeaderResponse = headerResponse
            };
        }

我的工厂class：

public static class ResponseFactory
    {
        public static IResponse CreateResponse()
        {
            return new Response();
        }

        public static IResponse CreateDeleteResponse()
        {
            return new DeleteShipmentResponse();
        }

        public static IResponse CreateShipmentResponse()
        {
            return new ShipmentResponse();
        }

        public static T CreateResponse<T>()
        where T : IResponse
        {
            return (T)CreateResponse(typeof(T));
        }

        public static IResponse CreateResponse(Type type) 
        {
            if (type == typeof(Response))
                return CreateResponse();
            if (type == typeof(DeleteShipmentResponse))
                return CreateDeleteResponse();
            else if (type == typeof(ShipmentResponse))
                return CreateShipmentResponse();
            else
                throw new ArgumentOutOfRangeException(string.Format(CultureInfo.InvariantCulture, "Unrecognized type [{0}]", type.FullName), "type");
        }
    }

因此，当我使用工厂创建 DeleteShipmentResponse 并调用 SetExeceptionResponse 时，我这样做了：

DeleteShipmentResponse result = (DeleteShipmentResponse)ResponseFactory.CreateResponse<DeleteShipmentResponse>().SetExceptionResponse(500, "Exception in DeleteShipment()", new string[] { ex.Message });

我必须使用 DeleteShipmentResponse 进行转换，否则会抛出异常。

如何在不强制转换为 DeleteShipmentResponse 的情况下获得它？我必须使用通用接口吗？

感谢帮助

Answer 1

如果所有 IResponse 都可以有一个无参数的构造函数，您可以使 IResponse 泛型“自身”，即 T 约束为 IResponse<T>:

public interface IResponse<T> where T : IResponse<T>
{
    int ErrorCode { get; set; }

    HeaderResponse HeaderResponse { get; set; }

    T SetExceptionResponse(int code, string title, string[] errors);
}

public class Response<T> : IResponse<T> where T : IResponse<T>, new
{
    public int ErrorCode { get; set; }

    public HeaderResponse HeaderResponse { get; set; } = null;
    public virtual T SetExceptionResponse(int code, string title, string[] errors)
    {
        HeaderResponse headerResponse = new HeaderResponse();
        .....    
        return new T
        {
            ErrorCode = code,
            HeaderResponse = headerResponse
        };
    }
}

public class DeleteShipmentResponse : Response<DeleteShipmentResponse>
{
    ...

    public override DeleteShipmentResponse SetExceptionResponse(int code, string title, string[] errors)
    {
        ....
        return new DeleteShipmentResponse
        {
            ErrorCode = code,
            HeaderResponse = headerResponse
        };
    }
}

带接口的工厂模式，如何避免转换

Factory pattern with interface, how to avoid cast

c#

generics

interface

factory