使用C＃从URL获取内容会收到此错误“ WebRequest不包含GetRespone和…的定义”

Question

This code comes from Microsoft's documentation. I put this code in a Console app and a Windows Form app separately.

In the Console app, there is an error : “WebRequest does not contain a definition for GetRespone and …”

But in the Windows Form app, there is no error.

I really don't know why this happen. I am a beginner of C#, so this question may be stupid. But I feel very confused. Please explain to me. Thank you!

Below are two screenshots for these two situation:

Here is the code.

using System;
using System.IO;
using System.Net;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a request for the URL.   
            WebRequest request = WebRequest.Create(
              "http://www.contoso.com/default.html");
            // If required by the server, set the credentials.  
            request.Credentials = CredentialCache.DefaultCredentials;
            // Get the response.  
            WebResponse response = request.GetResponse();
            // Display the status.  
            Console.WriteLine(((HttpWebResponse)response).StatusDescription);
            // Get the stream containing content returned by the server.  
            Stream dataStream = response.GetResponseStream();
            // Open the stream using a StreamReader for easy access.  
            StreamReader reader = new StreamReader(dataStream);
            // Read the content.  
            string responseFromServer = reader.ReadToEnd();
            // Display the content.  
            Console.WriteLine(responseFromServer);
            // Clean up the streams and the response.  
            reader.Close();
            response.Close();
        }
    }
}

Update 1:

I was using Macbook Pro by the parallel virtual machine and the VS version is Enterprise 2017, .net framework is 4.5.2.

But after I shifted to a windows laptop, and the code is running perfect. Maybe the problem is the virtual machine ? ... It's very strange. It seems that I can't just trust to the virtual machine... Anyway, Thanks for helping !

Update 2:

It seems that I was too optimistic. When I use Visual Studio 2017, even I build it on Windows Laptop, the error still shown. So, I think there is a high chance that the problem is Visual Studio 2017...

Answer 1

It looks like reader.Close() is also complaining, which leads me to believe one or more of your referenced assemblies is missing. Can you check the References folder in your project and see if any have a yellow warning icon on them?

Answer 2

You must use an HttpWebRequest and HttpWebResponse, not a WebRequest:

using System;
using System.IO;
using System.Net;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a request for the URL.   
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
              "http://www.contoso.com/default.html");
            // If required by the server, set the credentials.  
            request.Credentials = CredentialCache.DefaultCredentials;
            // Get the response.  
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            // Get the stream containing content returned by the server.  
            Stream dataStream = response.GetResponseStream();
            // Open the stream using a StreamReader for easy access.  
            StreamReader reader = new StreamReader(dataStream);
            // Read the content.  
            string responseFromServer = reader.ReadToEnd();
            // Display the content.  
            Console.WriteLine(responseFromServer);
            // Clean up the streams and the response.  
            reader.Close();
            response.Close();
        }
    }
}

WebRequest.Create will create a derived class of WebRequest with the exact implementation (HttpWebRequest, FtpWebRequest and so on) for the specified address, so you must cast to the concrete implementation to access the concrete functions.

Also, as HttpWebRequest.GetResponse returns the concrete implementation of WebResponse you must cast it, in this case to HttpWebResponse.