In this short article, I’ll show you how to send data to a website from a C# application using GET or POST method. The tutorial also includes how to receive data from a website, by getting the page’s source - so it’s a neat way to check if the everything is working as intended.

1. GET Method

Using the GET method is the easiest way to send any text data since all you have to do is to open the Url address with already-defined parameters, with WebClient. Notice that WebClient is IDisposable you can use it this way:

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string username = "john";
string urlAddress = "http://www.yoursite.tld/somepage.php?username=" + username;  

using (WebClient client = new WebClient())
{
       // this string contains the webpage's source
       string pagesource = client.DownloadString(urlAddress);  
}

The code above opens a Url address, with 1 GET parameter: /somepage.php?username=john.

Now if you need to check what the program sent, use a PHP snippet like this one and look in the source of the page:

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<?php
    $username = $_GET["username"];  //make sure you filter these values, before showing them
    echo $username;  //$username == "john"
?>

2. POST Method

Sending data using POST, even if it looks similar to GET, you’ll need a different approach. Not very different, we’re still using WebClient, but we must also include a new class: NameValueCollection. This dictionary-like container will store each parameter’s name and value. Once all the data has been loaded, call WebClient.UploadValues to send the information to the webpage.

First, make sure you include this namespace:

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using System.Collections.Specialized;

Then, you can jump to the code:

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string username = "john";
string referer = "myprogram";
string urlAddress = "http://www.yoursite.tld/somepage.php";

using (WebClient client = new WebClient())
{
       NameValueCollection postData = new NameValueCollection() 
       { 
              { "username", username },  //order: {"parameter name", "parameter value"}
              { "referer", referer }
       };

       // client.UploadValues returns page's source as byte array (byte[])
       // so it must be transformed into a string
       string pagesource = Encoding.UTF8.GetString(client.UploadValues(urlAddress, postData));
}

Once again, a short PHP snippet that can be used with the example above (the result is shown in the source code, downloaded by WebClient.UploadValues):

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<?php
    $username = $_POST["username"];  
    $referer = $_POST["referer"];
    echo $username." from ".$referer;  // $username == "john" and $referer == "myprogram"
?>