Dynamic loading of images in WPF

Question

I have a strange issue with WPF, I was loading images from the disk at runtime and adding them to a StackView container. However, the images were not displayed. After some debugging I found the trick, but it really doesn't make any sense. I've made a small demo app to identify the problem:

Create a new WPF project, and paste code as follows:

xaml:

<Window x:Class="wpfBug.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <StackPanel Name="sp">
    </StackPanel>
</Window>

xaml.cs, paste below default usings:

namespace wpfBug
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            Image i = new Image();
            BitmapImage src = new BitmapImage();
            src.BeginInit();
            src.UriSource = new Uri("picture.jpg", UriKind.Relative);
            src.EndInit();
            i.Source = src;
            i.Stretch = Stretch.Uniform;
            //int q = src.PixelHeight;        // Image loads here
            sp.Children.Add(i);
        }
    }
}

Copy a image to the bin/Debug folder and call it 'picture.jpg'

This program doesn't display anything, unless the commented line is uncommented.

Can anyone explain what I'm doing wrong, or why this happens? If you remove the image and run the program it generates an exception on the 'int q= ...' line. If that line is commented the program runs without exceptions even if no image is present. Loading an image only if nessesary makes sense, but then the image should be loaded when I add the Image control to the StackPanel.

Any ides ?

Edit: By the way, if you add the image as a resource, the 'int q = ..' line is not needed.

Answer 1

It is because the Creation was delayed. If you want the picture to be loaded immediately, you can simply add this code into the init phase.

src.CacheOption = BitmapCacheOption.OnLoad;

like this:

src.BeginInit();
src.UriSource = new Uri("picture.jpg", UriKind.Relative);
src.CacheOption = BitmapCacheOption.OnLoad;
src.EndInit();