C#:将基类转换为子类 [英] C# : Converting Base Class to Child Class

问题描述

我有一个类 NetworkClient 作为基类:

I have a class, NetworkClient as a base class :

using System.IO;
using System.Net.Sockets;
using System.Threading.Tasks;

namespace Network
{
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class NetworkClient
{
    public NetworkClient()
    {
        tcpClient = new TcpClient();
    }
    public NetworkClient(TcpClient client)
    {
        tcpClient = client;
    }

    public virtual bool IsConnected
    {
        get;
        private set;
    }
    private StreamWriter writer { get; set; }
    private StreamReader reader { get; set; }

    private TcpClient tcpClient
    {
        get;
        set;
    }

    public virtual NetworkServerInfo NetworkServerInfo
    {
        get;
        set;
    }

    public async virtual void Connect(NetworkServerInfo info)
    {
        if (tcpClient == null)
        {
            tcpClient=new TcpClient();
        }
        await tcpClient.ConnectAsync(info.Address,info.Port);
        reader = new StreamReader(tcpClient.GetStream());
        writer = new StreamWriter(tcpClient.GetStream());
    }

    public virtual void Disconnect()
    {
        tcpClient.Close();            
        reader.Dispose();

        writer.Dispose();
    }

    public async virtual void Send(string data)
    {
        await writer.WriteLineAsync(data);
    }

    public async virtual Task<string> Receive()
    {
        return await reader.ReadLineAsync();
    }

}
}

还有一个从 NetworkClient 派生的子类:

And also have a child class derived from NetworkClient :

using System.Net;

namespace Network
{
using Data;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class SkyfilterClient : NetworkClient
{
    public virtual IPAddress Address
    {
        get;
        set;
    }

    public virtual int Port
    {
        get;
        set;
    }

    public virtual string SessionID
    {
        get;
        set;
    }

    public virtual User UserData
    {
        get;
        set;
    }

    protected virtual bool Authenticate(string username, string password)
    {
        throw new System.NotImplementedException();
    }

}
}

问题是，当我尝试将 NetworkClient 转换为 SkyfilterClient 时.抛出异常，无法将Network.NetworkClient"类型的对象转换为Network.SkyfilterClient"类型.

The problem is, that when im trying to cast NetworkClient into SkyfilterClient. An exception is thrown, Unable to cast object of type 'Network.NetworkClient' to type 'Network.SkyfilterClient'.

我的代码有什么问题?我看到Stream可以转换为NetworkStream，MemoryStream.为什么 NetworkClient 无法转换为 Skyfilter Client?

Whats wrong with my code ? I see that Stream can be converted to NetworkStream, MemoryStream. Why NetworkClient can't be converted to Skyfilter Client?

推荐答案

只要对象实际上是一个 SkyfilterClient，那么演员表就应该起作用.这是一个人为的例子来证明这一点:

As long as the object is actually a SkyfilterClient, then a cast should work. Here is a contrived example to prove this:

using System;

class Program
{
    static void Main()
    {
        NetworkClient net = new SkyfilterClient();
        var sky = (SkyfilterClient)net;
    }
}

public class NetworkClient{}
public class SkyfilterClient : NetworkClient{}

然而，如果它实际上是一个NetworkClient，那么你不能神奇地使它成为子类.下面是一个例子:

However, if it is actually a NetworkClient, then you cannot magically make it become the subclass. Here is an example of that:

using System;

class Program
{
    static void Main()
    {
        NetworkClient net = new NetworkClient();
        var sky = (SkyfilterClient)net;
    }
}

public class NetworkClient{}
public class SkyfilterClient : NetworkClient{}

但是，您可以创建一个转换器类.这里还有一个例子:

HOWEVER, you could create a converter class. Here is an example of that, also:

using System;

class Program
{
    static void Main()
    {
        NetworkClient net = new NetworkClient();
        var sky = SkyFilterClient.CopyToSkyfilterClient(net);
    }
}

public class NetworkClient
{  
  public int SomeVal {get;set;}
}

public class SkyfilterClient : NetworkClient
{
    public int NewSomeVal {get;set;}
    public static SkyfilterClient CopyToSkyfilterClient(NetworkClient networkClient)
    {
        return new SkyfilterClient{NewSomeVal = networkClient.SomeVal};
    }
}

但是，请记住，您无法以这种方式进行转换是有原因的.您可能缺少子类所需的关键信息.

But, keep in mind that there is a reason you cannot convert this way. You may be missing key information that the subclass needs.

最后，如果你只是想看看尝试的转换是否有效，那么你可以使用is:

Finally, if you just want to see if the attempted cast will work, then you can use is:

if(client is SkyfilterClient)
    cast

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