Accessing HTTP Web Services

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YDN Silverlight Developer Center

Silverlight: Accessing HTTP Web Services

Overview
Using the WebClient Class
Using the HttpWebRequest Class
Further Reading

Overview

There are two main classes used in Silverlight to access HTTP web services, WebClient and HttpWebRequest.

Using the `WebClient` Class

The WebClient class is suitable for most GET and POST requests and is easier to use than HttpWebRequest as it requires less code and due to its event-based model that returns data on the UI thread.

Download As a String

The following example shows how to download a file as a string and write the contents to the debug output.

C# Example

using System;
using System.Diagnostics;
using System.Net;
using System.Text;
using System.Windows.Browser;
using System.Windows.Controls;

namespace SilverlightApplication3
{
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();

GetFileAsString();
        }

private void GetFileAsString()
        {
            var stringClient = new WebClient();

// Hook event handler
            stringClient.DownloadStringCompleted 
			  += new DownloadStringCompletedEventHandler(sClient_DownloadStringCompleted);

// Start download
            stringClient.DownloadStringAsync(
			  new Uri("../SampleText.txt", UriKind.Relative), "myToken");
        }

private void sClient_DownloadStringCompleted(
						object sender, DownloadStringCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                Debug.WriteLine("Token: " + e.UserState + ", Data: " + e.Result);
            }
            else
            {
                // Handle error
                Debug.WriteLine(e.Error);
            }
        }
    }
}

Visual Basic Example

Download As a Stream

The following example shows how to download a file as a stream and write the contents to the debug output. Normally you would use either the XmlReader or the DataContractJsonSerializer class to work with the response.

C# Example

Visual Basic Example

Make a POST Request

The following example shows how to make a POST request, download the result as a string, and write the contents to the debug output.

C# Example

private void PostString()
        {
            var postClient = new WebClient();

// Hook event handler
            postClient.UploadStringCompleted 
                += new UploadStringCompletedEventHandler(pClient_UploadStringCompleted);

var address = new Uri("../Request.aspx", UriKind.Relative);

// Create the data we want to send
            string appId = "YahooDemo";
            string context = "Italian sculptors and painters of the ...";
            string query = "madonna";
            StringBuilder data = new StringBuilder();
            data.Append("appid=" + HttpUtility.UrlEncode(appId));
            data.Append("&context=" + HttpUtility.UrlEncode(context));
            data.Append("&query=" + HttpUtility.UrlEncode(query));

// Set headers and make POST request
            postClient.Headers["Content-Type"] = "application/x-www-form-urlencoded";
            postClient.UploadStringAsync(address, data.ToString());
        }

private void pClient_UploadStringCompleted(object sender, UploadStringCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                Debug.WriteLine(e.Result);
            }
            else
            {
                // Handle error
                Debug.WriteLine(e.Error);
            }
        }

Visual Basic Example

Private Sub PostString()

Dim postClient As New WebClient

' Hook event handler
        AddHandler postClient.UploadStringCompleted, _
            New UploadStringCompletedEventHandler( _
                AddressOf pClient_UploadStringCompleted)

Dim address As New Uri("../Request.aspx", UriKind.Relative)

' Create the data we want to send
        Dim appId As String = "YahooDemo"
        Dim context As String = "Italian sculptors and painters of the renaissance..."
        Dim query As String = "madonna"
        Dim data As New StringBuilder

data.Append(("appid=" & HttpUtility.UrlEncode(appId)))
        data.Append(("&context=" & HttpUtility.UrlEncode(context)))
        data.Append(("&query=" & HttpUtility.UrlEncode(query)))

' Set headers and make POST request
        postClient.Headers.Item("Content-Type") = "application/x-www-form-urlencoded"
        postClient.UploadStringAsync(address, data.ToString)

End Sub

Private Sub pClient_UploadStringCompleted(ByVal sender As Object, _
                                              ByVal e As UploadStringCompletedEventArgs)

If (e.Error Is Nothing) Then
            Debug.WriteLine(e.Result)
        Else
            Debug.WriteLine(e.Error)
        End If

End Sub

Using the `HttpWebRequest` Class

The HttpWebRequest supports a larger subset of the HTTP protocol, but uses a delegate-based callback mechanism and requires that any calls to the UI thread be marshaled appropriately. Please refer to the Silverlight documentation for details and samples.

Silverlight: Accessing HTTP Web Services

Overview

Using the WebClient Class

Download As a String

C# Example

Visual Basic Example

Download As a Stream

C# Example

Visual Basic Example

Make a POST Request

C# Example

Visual Basic Example

Using the HttpWebRequest Class

Further Reading

Using the `WebClient` Class

Using the `HttpWebRequest` Class