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POWhy does a WPF BitmapImage object not download an image from a Uri Source in ASP.Net Web Forms?
 

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  1. POWhy does a WPF BitmapImage object not download an image from a Uri Source in ASP.Net Web Forms?
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    <p>I'm trying to accomplish the following in ASP.Net:</p> <ol> <li>Create a WPF Canvas control</li> <li>Spin up a WPF Image control and a BitmapImage object</li> <li>Set the BitmapImage source to a Uri for an image</li> <li>Add the image to the canvas</li> <li>When the image is downloaded render the canvas to a new bitmap</li> </ol> <p>My code works correctly in WPF itself, however when running in an ASP.Net page the image is not downloaded.</p> <p>It works totally fine for other WPF UI elements. In the case of Image, using the BitmapImage.StreamSource property to set the source works correctly. When I use the BitmapImage.UriSource property the BitmapImage.DownloadCompleted event isn't raised, which hints that the image never starts downloading in the first place.</p> <p>It's important to note that it works fine for most controls - ellipses, rectangles, ink presenters, and also the Image control so long as I use a stream source rather than a uri source.</p> <p>So, what am I missing here? Why does the BitmapImage class behave differently in a web application?</p> <p>I know I'll get asked so the purpose in doing this is that I have written a Silverlight client to create graphical content which is stored on a web server. I want the web server to render the content to bitmap files.</p> <p>Thanks in advance for any advice..</p> <p>Here's my code for the ASP.Net page:</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Windows.Controls; using System.Windows.Media.Imaging; using System.Threading; using System.Windows; using System.Net; using System.IO; using System.Windows.Media; public partial class _Default : System.Web.UI.Page { private static Canvas c; protected void Page_Load(object sender, EventArgs e) { Thread t = new Thread(new ThreadStart( delegate { DownloadAndSave(); })); t.SetApartmentState(ApartmentState.STA); t.Start(); t.Join(); } [STAThread] void DownloadAndSave() { c = new Canvas(); BitmapImage bitmap = new BitmapImage(); System.Windows.Controls.Image image = new System.Windows.Controls.Image(); bitmap.DownloadCompleted += new EventHandler(bitmap_DownloadCompleted); bitmap.BeginInit(); bitmap.UriSource = new Uri("http://andrew.myhre.tanash.net/customassets/andrewmyhre/image/face.jpg"); bitmap.EndInit(); image.Source = bitmap; c.Children.Add(image); c.UpdateLayout(); c.Measure(new Size(400, 300)); c.Arrange(new Rect(new Size(400, 300))); } void bitmap_DownloadCompleted(object sender, EventArgs e) { // this never fires!! SaveImage(c); } void SaveImage(UIElement element) { RenderTargetBitmap bmp = new RenderTargetBitmap(400, 300, 96, 96, PixelFormats.Pbgra32); bmp.Render(element); BitmapEncoder encoder = new JpegBitmapEncoder(); encoder.Frames.Add(BitmapFrame.Create(bmp)); using (Stream stm = File.Create(Server.MapPath("~/file.jpg"))) encoder.Save(stm); } } </code></pre>
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