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Is there any way to inherit a class without constructors in .NET?

StackOverflow https://stackoverflow.com/questions/400565

Question

I'm currently trying to modify some HttpWebRequest functions, but I can't do it through inheritance because HttpWebRequest has no public constructors (besides the deserialization constructor). Is there a workaround to do this?

My objective is to code something like the example below, but this class objects must inherit the HttpWebRequest properties and methods:

using System;
using System.Net;
using System.Threading;

public class AsyncWebRequest:WebRequest
{
    private readonly AsyncCallback getResponseCallback;
    private readonly Uri uri;
    private volatile int RetriesLeft = 3;
    private volatile WebRequest request;

    public AsyncWebRequest(string uri, AsyncCallback getResponseCallback)
       :this(new Uri(uri), getResponseCallback)
    {
    }

    public AsyncWebRequest(Uri uri, AsyncCallback getResponseCallback):base()
    {
        this.uri = uri;
        this.getResponseCallback = getResponseCallback;
    }

    private IAsyncResult BeginGetResponse()
    {
        request = HttpWebRequest.CreateDefault(uri);
        ((HttpWebRequest)request).ReadWriteTimeout = Timeout;
        var result = request.BeginGetResponse(GetResponseCallback, null);
        ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle,
            GetResponseTimeout, null, Timeout, true);
        return result;
    }

    private void GetResponseTimeout(object state, bool timedOut)
    {
        if (timedOut)
        {
            Retry();
        }
    }

    private void Retry()
    {
        request.Abort();
        bool retry = false;
        lock (request)
        {
            if (RetriesLeft > 0)
            {
                Interlocked.Decrement(ref RetriesLeft);
                retry = true;
            }
        }
        if (retry)
        {
            BeginGetResponse();
        }
        else
        {
            getResponseCallback(null);
        }
    }

    private void GetResponseCallback(IAsyncResult AsyncResult)
    {
        try
        {
            getResponseCallback(AsyncResult);
        }
        catch(WebException webException)
        {
            Retry();
        }
    }
}

Solution

Unless you can trick the serialization constructor to do your bidding, then no, there is no way.

The constructors of that class are internal, so you have no way of calling them.

OTHER TIPS

You can't through inheritance from HttpWebRequest (if you don't want to call the serialization constructor) , but you can through composition and delegation, and through inheritance from WebRequest (I'm not sure if that will do it for you, but functionally it is quite similar). WebRequest has a default constructor.

In this case you then can't have the class 'be' a HttpWebRequest (as in an is-a relationship), since you can't extend from it, but it wil 'be' a WebRequest, which should suffice.

You could write a class that inherits from WebRequest, that has an instance member of type WebRequest, create a HttpWebRequest and assign to instance member in the constructor of the new type and delegate all calls to that reference (sort of a decorator pattern):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;

namespace ClassLibrary1
{
    public class MyHttpWebRequest : WebRequest
    {
        private WebRequest request;

        public MyHttpWebRequest(string uri)
        {
            request = HttpWebRequest.Create(uri);
        }

        public override WebResponse GetResponse()
        {
            // do your extras, or just delegate to get the original code, as long
            // as you still keep to expected behavior etc.
            return request.GetResponse();
        }

    }
}

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