How do you login to a webpage and retrieve its con

问题:

How do you login to a webpage and retrieve its content in C#?

回答1:

That depends on what's required to log in. You could use a webclient to send the login credentials to the server's login page (via whatever method is required, GET or POST), but that wouldn't persist a cookie. There is a way to get a webclient to handle cookies, so you could just POST the login info to the server, then request the page you want with the same webclient, then do whatever you want with the page.

回答2:

Look at System.Net.WebClient, or for more advanced requirements System.Net.HttpWebRequest/System.Net.HttpWebResponse.

As for actually applying these: you'll have to study the html source of each page you want to scrape in order to learn exactly what Http requests it's expecting.

回答3:

How do you mean "login"?

If the subfolder is protected on the OS level, and the browser pops of a login dialog when you go there, you will need to set the Credentials property on the HttpWebRequest.

If the website has it's own cookie-based membership/login system, you will have to use HttpWebRequest to first response to the login form.

回答4:

string postData = "userid=ducon";
            postData += "&username=camarche" ;
            byte[] data = Encoding.ASCII.GetBytes(postData);
            WebRequest req = WebRequest.Create(
                URL);
            req.Method = "POST";
            req.ContentType = "application/x-www-form-urlencoded";
            req.ContentLength = data.Length;
            Stream newStream = req.GetRequestStream();
            newStream.Write(data, 0, data.Length);
            newStream.Close();
            StreamReader reader = new StreamReader(req.GetResponse().GetResponseStream(), System.Text.Encoding.GetEncoding("iso-8859-1"));
            string coco = reader.ReadToEnd();

回答5:

Use the WebClient class.

Dim Html As String

Using Client As New System.Net.WebClient()
    Html = Client.DownloadString("http://www.google.com")
End Using

回答6:

You can use the build in WebClient Object instead of crating the request yourself.

WebClient wc = new WebClient();
wc.Credentials = new NetworkCredential("username", "password");
string url = "http://foo.com";          
try
{
    using (Stream stream = wc.OpenRead(new Uri(url)))
    {
        using (StreamReader reader = new StreamReader(stream))
        {
            return reader.ReadToEnd();
             }
    }
}
catch (WebException e)
{
    //Error handeling
}

回答7:

Try this:

public string GetContent(string url)  
{ 
  using (System.Net.WebClient client =new System.Net.WebClient()) 
  { 
  return client.DownloadString(url); 
  } 
}