C# 通用工厂法铸造问题

尝试创建工厂以返回通用接口（如下所示），但出现错误：

无法将

IFinancialsSyncService

隐式转换为

IFinancialsSyncService

。存在明文转换，是否缺少强制转换

但是，如果我显式地强制转换它，我会得到一个

强制转换是冗余的

错误以及第一个错误

return (IFinancialsSyncService<Vendor, QuickBooksVendor>)new QuickbooksVendorService();

并将其替换为以下内容：

var qbEntityService = EntityServiceFactory.Create(enumDataElement);

---

这个工厂会是什么样子？

这与利斯科夫的替代原理有关。假设您的泛型类型是接口的一个属性：

public class QuickbooksVendorService : IFinancialsSyncService<Vendor, QuickBooksVendor>

public interface IFinancials { }

public interface IFinancialsSyncService
{
  IFinancials Financials { get; set; }
}

现在我们实现以下接口：

public class Financials : IFinancials {}

public class FinancialsSyncService : IFinancialSyncService
{
  public Financials Financials { get; set; }
}

这将导致编译器错误：

编译错误：“Program.FinancialSyncService”未实现接口成员“Program.IFinancialsSyncService.Financials”Program.FinancialSyncService.Financials无法实现Program.IFinancialsSyncService.Financials，因为它没有匹配的返回类型“Program.IFinancials”

这两个问题都有相同的问题。在我的示例中，接口声明结果的类型为

IFinancials

，但它是更具体的派生类型

Financials

，即使放置在属性中的任何有效值满足接口，它不能替换为从

IFinancials

派生的任何值，只能替换为从

Financials

派生的类型

因此，如果您的代码看起来像：

public interface IFinancialsSyncService<TEntity>
   where TEntity : IEntity
{
  TEntity Financials { get; set; }
}

公共接口IFinancialsSyncService
其中tenty:tenty
{
TEntity Financials{get；set；}
}

然后创建一个类：

public class QuickbooksVendorService : IFinancialSyncService<Vendor>
{
  public Vendor Financials { get; set; }
}

公共类QuickbooksVendorService:IFinancialSyncService
{
公共供应商财务{get；set；}
}

---

但是，现在

QuickbooksVendorService

是

IFinancialSyncService

而不是

IFinancialSyncService

，因为该属性是派生类型。即使您没有此特定属性，它仍然会导致相同的问题，即泛型类型比接口更具体。

使用工厂方法和适配器模式

switch (enumDataElement)
{
    //Export jobs
    case DataElement.Item:
        var itemService = new QuickbooksItemService();
        exportResult = itemService.UpdateMozzoEntityWithFinancialsId(session, response, EntityId, intUserId);
        break;

    case DataElement.Vendor:
        var VendorService = new QuickbooksVendorService();
        exportResult = UpdateMozzoEntityWithFinancialsId(new QuickbooksVendorService(),session, response, EntityId, intUserId);
        break;

    case DataElement.Bill:
        var billService = new QuickbooksBillService();
        exportResult = billService.UpdateMozzoEntityWithFinancialsId(session, response, intUserId);
        break;

    case DataElement.PurchaseOrder:
        var qbPOService = new QuickbooksPurchaseOrderService();
        exportResult = qbPOService.UpdateMozzoEntityWithFinancialsId(session, response, intUserId);           
        break;

    case DataElement.SalesReceipt:
        var salesReceiptService = new QuickbooksSalesReceiptService();
        exportResult = salesReceiptService.UpdateStratusEntityWithFinancialsId(session, response, intUserId);
        break;
}

   [TestFixture]
    public class Class1
    {

        [Test]
        public void Go()
        {
            var qbItem = Export(1);
            var qbVendor= Export(2);
            var qbSales= Export(3);
        }

        public qbEntityService Export(int number)
        {
            var qb = Class1.Create(number);
            return qb.UpdateMozzoEntityWithFinancialsId();
        }

        public static IEntityService Create(int enumDataElement)
        {
            switch (enumDataElement)
            {
                case 1:
                    return new QuickbooksItemService();
                case 2:
                    return new QuickbooksVendorService();
                case 3:
                    return new QuickbooksSalesReceiptServiceAdapter(new QuickbooksSalesReceiptService());
                default:
                    throw new Exception();
            }
        }
    }

    public interface IEntityService
    {
        qbEntityService UpdateMozzoEntityWithFinancialsId();
    }

    public class qbEntityService
    {
    }

    public class QuickbooksItemService : IEntityService
    {
        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksItemService, performing UpdateMozzoEntityWithFinancialsId");
            return new qbEntityService();
        }
    }

    public class QuickbooksVendorService : IEntityService
    {
        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksVendorService, performing UpdateMozzoEntityWithFinancialsId");
            return new qbEntityService();
        }
    }

    public class QuickbooksSalesReceiptService
    {
        public qbEntityService UpdateStratusEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksSalesReceiptService, performing UpdateStratusEntityWithFinancialsId");
            return new qbEntityService();
        }
    }


    public class QuickbooksSalesReceiptServiceAdapter : IEntityService
    {
        private QuickbooksSalesReceiptService adaptee;

        public QuickbooksSalesReceiptServiceAdapter(QuickbooksSalesReceiptService adaptee)
        {
            this.adaptee = adaptee;
        }

        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            return adaptee.UpdateStratusEntityWithFinancialsId();
        }
    }

---

什么是供应商类型？它是否实现了智能？请检查QuickBooksVendor服务是否正确实现了IFinancialsSyncService。同时签入您的泛型方法TEntity实现IEntity和IFinancials，TQuickBooksEntity实现IQuickBooksEntity。@maxspan是的，它们都实现了正确的接口。谢谢Erik，因此您无法返回更具体的类型。我还有一些其他与实体相关的服务，类似于

QuickBooksVendorService

，它们都符合相同的接口。我正在寻找一个工厂，根据输入类型返回正确的一个。我只需要使用两种方法，它们都是通用的，都是接口定义的一部分。那么，我如何创建一个工厂来返回这些服务中的一项……工厂的常见返回类型是什么？还是我走错了路？注意，已更新的问题显示了我试图消除的内容。我想问您为什么要返回通用接口

InterfaceOf

，而不仅仅是接口

Interface

。你没有说谁在使用结果，所以很难知道。是的，我能够从接口中删除返回

tenty

和

TQuickBooksEntity

的方法，并删除接口的那些限定符。工厂工作正常，然后只返回接口

IFinancialSyncService

。但是我想将这些方法恢复到接口。主要原因是，由于这是一个适配器类型的项目，它正在检索QuickBooks实体，如发票，然后将其转换为我们应用程序版本的发票，然后导入我们的应用程序数据库。@ChadRichardson您需要修复第59行和第62行。@ChadRichardson删除了更多未使用的泛型。

   [TestFixture]
    public class Class1
    {

        [Test]
        public void Go()
        {
            var qbItem = Export(1);
            var qbVendor= Export(2);
            var qbSales= Export(3);
        }

        public qbEntityService Export(int number)
        {
            var qb = Class1.Create(number);
            return qb.UpdateMozzoEntityWithFinancialsId();
        }

        public static IEntityService Create(int enumDataElement)
        {
            switch (enumDataElement)
            {
                case 1:
                    return new QuickbooksItemService();
                case 2:
                    return new QuickbooksVendorService();
                case 3:
                    return new QuickbooksSalesReceiptServiceAdapter(new QuickbooksSalesReceiptService());
                default:
                    throw new Exception();
            }
        }
    }

    public interface IEntityService
    {
        qbEntityService UpdateMozzoEntityWithFinancialsId();
    }

    public class qbEntityService
    {
    }

    public class QuickbooksItemService : IEntityService
    {
        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksItemService, performing UpdateMozzoEntityWithFinancialsId");
            return new qbEntityService();
        }
    }

    public class QuickbooksVendorService : IEntityService
    {
        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksVendorService, performing UpdateMozzoEntityWithFinancialsId");
            return new qbEntityService();
        }
    }

    public class QuickbooksSalesReceiptService
    {
        public qbEntityService UpdateStratusEntityWithFinancialsId()
        {
            Console.WriteLine("I am QuickbooksSalesReceiptService, performing UpdateStratusEntityWithFinancialsId");
            return new qbEntityService();
        }
    }


    public class QuickbooksSalesReceiptServiceAdapter : IEntityService
    {
        private QuickbooksSalesReceiptService adaptee;

        public QuickbooksSalesReceiptServiceAdapter(QuickbooksSalesReceiptService adaptee)
        {
            this.adaptee = adaptee;
        }

        public qbEntityService UpdateMozzoEntityWithFinancialsId()
        {
            return adaptee.UpdateStratusEntityWithFinancialsId();
        }
    }