类实例不能分配给继承的接口答案

【问题标题】：class instance can not assign to inherited interface类实例不能分配给继承的接口
【发布时间】：2017-08-14 07:10:20
【问题描述】：

我有两个接口声明和三个类声明，它们之间的关系是这样的：

interface IProtocolPackage
{
 ///some declaration
}
public class ProtocolPackage : IProtocolPackage
{
 ///implementation code for IProtocolPackage
}
interface IProtocolPackage<T> : IProtocolPackage
{
 ///some declaration
}
public class BytesProtocolPackage : ProtocolPackage, IProtocolPackage<byte[]>
{
///implementation code for IProtocolPackage<byte[]>
}
public class ChargingPileProtocolPackage : BytesProtocolPackage
{
///implementation code for IProtocolPackage<byte[]>
}

然后有一个方法以 IProtocolPackage 类型为参数，如下所示：

public void DecodeCommand(IProtocolPackage<byte> package)
    {
        ///implementation code forDecodeCommand
    }

但编译器显示错误说：无法从“ChargingPileCommandCoder.ChargingPileProtocolPackage”转换为“SHWDTech.Platform.ProtocolCoding.Coding.IProtocolPackage”ChargingPileCommandCoder

我以为我继承了接口 IProtocolPackage 和类 ChargingPileProtocolPackage。这是怎么发生的？

发生错误的代码：

public IProtocolPackage DecodeProtocol(byte[] bufferBytes, Protocol matchedProtocol)
    {
        var package = new ChargingPileProtocolPackage { Protocol = matchedProtocol, ReceiveDateTime = DateTime.Now };

        var structures = matchedProtocol.ProtocolStructures.ToList();

        var currentIndex = 0;

        for (var i = 0; i < structures.Count; i++)
        {
            var structure = structures.First(obj => obj.StructureIndex == i);

            var componentDataLength = structure.StructureName == StructureNames.Data && structure.StructureDataLength == 0
                ? Globals.BytesToInt16(package["DataLength"].ComponentContent, 0, true)
                : structure.StructureDataLength;

            if (currentIndex + componentDataLength > bufferBytes.Length)
            {
                package.Status = PackageStatus.NoEnoughBuffer;
                return package;
            }

            if (structure.StructureName == StructureNames.Data)
            {
                DetectCommand(package, matchedProtocol);
                componentDataLength = package.Command.ReceiveBytesLength == 0 ? componentDataLength : package.Command.ReceiveBytesLength;
            }

            var component = new PackageComponent<byte[]>
            {
                ComponentName = structure.StructureName,
                DataType = structure.DataType,
                ComponentIndex = structure.StructureIndex,
                ComponentContent = bufferBytes.SubBytes(currentIndex, currentIndex + componentDataLength)
            };

            currentIndex += componentDataLength;

            package[structure.StructureName] = component;
        }

        DecodeCommand(package);

        return package;
    }

    public IProtocolPackage EncodeCommand(IProtocolCommand command, Dictionary<string, byte[]> paramBytes = null)
    {
        throw new NotImplementedException();
    }

    public void DoDelive(IProtocolPackage package, IPackageSource source)
    {
        throw new NotImplementedException();
    }

    public IDataConverter<byte> DataConverter { get; set; }

    public void DecodeCommand(IProtocolPackage<byte> package)
    {
        throw new NotImplementedException();
    }

    public void DetectCommand(IProtocolPackage<byte> package, IProtocol matchedProtocol)
    {
        throw new NotImplementedException();
    }
}

【问题讨论】：

检查命名空间是否相同，可能你在两个命名空间中有重复的接口定义？
发布您遇到实际错误的代码。您发布的代码似乎没有任何错误。
此错误在哪里发生？我看不到任何将一个类实例转换为另一个类实例的代码。

标签： c# interface casting

【解决方案1】：

ChargingPileCommandCoder 类实现了 IProtocolPackage<byte[]> 但没有 IProtocolPackage<byte>。

【讨论】：

【解决方案2】：

当我将它粘贴到 VS 中时，我首先会收到有关接口可访问性的警告。

将它们公开时，我收到消息称 ChargingPileProtocolPackage 不可分配给 IProtocolPackage，实际上这是正确的，因为它实现了 IProtocolPackage。

如下更改 DecodeCommand 的签名时，警告消失了：

public void DecodeCommand(IProtocolPackage<byte[]> package)

【讨论】：