`WebClient`

This downloads files from remote servers. We use the WebClient type in the System.Net namespace. We make network requests to Internet sites or other servers with an HTTP address.

In VB.NET programs, WebClient provides critical functionality for downloading webpages and other files. We can manage headers and test responses.

To start, the WebClient type is found in the System.Net namespace. Next, the WebClient is best used in the scope of a Using-block—this helps resource management.

Info The example demonstrates how you can set a request header by specifying the string of its key.

Finally We call the DownloadData function which receives the URL parameter and returns a byte array containing the resource's data.

Imports System.Net

Module Module1
    Sub Main()
        ' Resource acquisition statement.
        Using client As New WebClient
            ' Set one of the headers.
            client.Headers("User-Agent") = "Mozilla/4.0"

            ' Download data as byte array.
            Dim arr() As Byte = client.DownloadData("http://www.example.com/")

            ' Display result.
            Console.WriteLine(arr.Length)
        End Using
    End Sub
End Module
5821

Example 2

Next we set two headers, and then download the data. Then we read one of the response headers. The target website returns a Content-Encoding heading that corresponds.

And In this way, you can use the WebClient to test the web sites you develop for correctness.

Imports System.Net

Module Module1
    Sub Main()
        Using client As New WebClient
            ' Set one of the headers.
            client.Headers("User-Agent") = "Googlebot/2.1"
            client.Headers("Accept-Encoding") = "gzip"

            ' Download data.
            Dim arr() As Byte = client.DownloadData("http://www.dotnetperls.com/")

            ' Display result.
            Console.WriteLine(arr.Length)
            Console.WriteLine(client.ResponseHeaders("Content-Encoding"))
        End Using
    End Sub
End Module2092
gzip

Example 3

We can download a web page as a String, not a byte array. Often, strings are more easily used in other parts of your program, making the DownloadString method more convenient.

Note The DownloadString function behaves similarly to the DownloadData function, but instead of a byte array it returns a String.

Imports System.Net

Module Module1
    Sub Main()
        Using client As New WebClient
            ' Download the web page as a string.
            Dim value As String = client.DownloadString("http://www.dotnetperls.com/")
            ' Write the first characters of the result.
            Console.WriteLine(value.Substring(0, 15))
        End Using
    End Sub
End Module
<!doctype html>

Asynchronous

The WebClient type provides asynchronous functions. Often, we should prefer another threading construct such as BackgroundWorker.

WebClient provides essential functionality for many programs. Many .NET programs use WebClient extensively for programmatic acquisition of remote resources.