C＃：转换基类子类 [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();
    }

}
}

和也有一个孩子从类派生NetworkClient：

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，当我尝试投NetworkClient到SkyfilterClient。抛出一个异常，无法转换类型'Network.NetworkClient对象键入'Network.SkyfilterClient。

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'.

请告诉我错我的代码？我看到流可以被转换成的NetworkStream，MemoryStream的。为什么NetworkClient不能转换为Skyfilter客户？

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 ，然后浇铸应该工作。这里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{}

不过，如果它实际上是一个 NetworkClient ，那么你就不能奇迹般地使之成为子类。下面是一些例子：

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{}

不过，你可以创建一个转换器类。下面是一些例子，也：

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，是有原因的你不能转换这种方式。您可能会丢失，该子类需要的关键信息。

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，如果你只是想看看是否试图投会的工作，那么你可以使用是：

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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