Question

I’m loading an image to a background, and I want the silverlight canvas containing it all to resize to the image size (or maximum or minimum that I determine) of whatever the size of the image is. So I’ve done the following:

private int ImageMargin = 4;

    public Page()
    {
        InitializeComponent();

        BitmapImage bi = new BitmapImage(new Uri("1.jpg", UriKind.Relative));
        backgroundImage.Source = bi;
        bi.DownloadProgress += new EventHandler<DownloadProgressEventArgs>(bi_DownloadProgress);

        backgroundImage.SizeChanged += new SizeChangedEventHandler(backgroundImage_SizeChanged);

    }

    void bi_DownloadProgress(object sender, DownloadProgressEventArgs e)
    {
        if (e.Progress == 100)
        {
          LayoutRoot.Height = backgroundImage.Height + ImageMargin * 2;
          LayoutRoot.Width = backgroundImage.Width + ImageMargin * 2;
        }
    }

The image loads correctly, but no matter where I seem to put the backgroundImage.Height/Width (off .Loaded event, .SizeChanged event [1], Using a border [2], etc), it always returns 0.0 or NaN. What am I doing wrong?

[1] http://silverlight.net/forums/t/14855.aspx
[2] http://silverlight.net/forums/t/90235.aspx

Answer 1

Ah, solution! Silverlight Tip of the Day #13 – How to Get an Images Dimensions in Silverlight.

private Image image;

    public Page()
    {
        InitializeComponent();
        LoadImage("image.png");
    }

    private void LoadImage(string path)
    {

        Uri uri = new Uri(path, UriKind.Relative);
        BitmapImage bitmapImage = new BitmapImage();
        bitmapImage.UriSource = uri;
        bitmapImage.DownloadProgress += 
            new EventHandler<DownloadProgressEventArgs>(bitmapImage_DownloadProgress);
    }

    void bitmapImage_DownloadProgress(object sender, DownloadProgressEventArgs e)
    {
        if (e.Progress == 100)
        {
            Dispatcher.BeginInvoke(delegate()
            {
               double height = image.ActualHeight;
               double width = image.ActualWidth;
            });
        }
    }

The KEY was this line:

The call to
Dispatcher.BeginInvoke(delegate() { …
} ); is required before you obtain the
Width/Height or they might be
intermittently zero.