Dr. Dobb's is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Channels ▼


Working with Events in Silverlight

Using Events to Download Files

Silverlight events can also be used in other ways that don't involve require user interaction. In Silverlight you can use a built-in Downloader object to download files used by an application on-the-fly. This functionality is useful when you need to download several images as an application initializes or need to download XAML fragments or other file types on demand as a user performs an action.

The Silverlight Downloader object exposes three events as in Table 2.




Fires when a download completes.


Fires when a download fails due to no content being returned.


Fires as a download progresses and provides the percentage of the file that has been downloaded.

Table 1

Listing Three provides an example of using the Silverlight Downloader object and handling its events. The code starts by creating the Silverlight object instance using the standard Silverlight.createObjectEx() method. Within this method the onLoad event is hooked to an event handler of the same name. The onLoad() event handler creates the Downloader control using the CreateObject() method and then wires its events to their respective event handlers using the AddEventListener() method. Once the events are wired up it then defines the file to download and calls Send() to start the download.

As the file is downloaded the onDownloadProgressChanged() event handler is called which is used to get the download progress. The code then updates a TextBlock object's Text property with the percentage of the download that has completed. When the file download completes the onCompleted() event handler is called which provides the user with an updated status.

var _TB = null;
function CreateSilverlight()
      source: "MyApp.xaml",
      parentElement: document.body,
      id: "slControl",
      properties: { width: "100%", height: "100%", version: "1.0" },
      events: { onLoad: onLoad, onError: null }
function onLoad(control, context, rootElement)
    _TB = control.Content.FindName("tbProgress");
    var downloader = control.CreateObject("downloader");
    downloader.AddEventListener("Completed", onCompleted);
    downloader.AddEventListener("DownloadFailed", onDownloadFailed);
    downloader.Open("GET", "MyFiles.zip?" + new Date()); 
function onDownloadProgressChanged(sender, eventArgs)
    var percentComplete = sender.DownloadProgress * 100;
    _TB.Text = Math.floor(percentComplete) + "%";
function onCompleted(sender, eventArgs)
    _TB.Text = "Download complete!";
    //Access files that were downloaded
Function onDownloadFailed(sender, eventArgs)
    //eventArgs will always be null in this event handler
    alert("Download failed");
Listing Three: Handling events exposed by Silverlight's Downloader object.


Events are where it's at in the world of application development. By defining events in XAML and handling them in JavaScript you can build a Silverlight application that is responsive to end user actions.

Related Reading

More Insights

Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.