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    lt 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  gt       lt StackPanel Name  sp  gt       lt  StackPanel gt   lt  Window gt    xaml cs  paste below default usings   namespace wpfBug            lt summary gt          Interaction logic for Window1 xaml          lt  summary gt      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

User · Answer

This is strange behavior and although I am unable to say why this is occurring, I can recommend some options.

First, an observation. If you include the image as Content in VS and copy it to the output directory, your code works. If the image is marked as None in VS and you copy it over, it doesn't work.

Solution 1: FileStream

The BitmapImage object accepts a UriSource or StreamSource as a parameter. Let's use StreamSource instead.

        FileStream stream = new FileStream("picture.png", FileMode.Open, FileAccess.Read);
        Image i = new Image();
        BitmapImage src = new BitmapImage();
        src.BeginInit();
        src.StreamSource = stream;
        src.EndInit();
        i.Source = src;
        i.Stretch = Stretch.Uniform;
        panel.Children.Add(i);

The problem: stream stays open. If you close it at the end of this method, the image will not show up. This means that the file stays write-locked on the system.

Solution 2: MemoryStream

This is basically solution 1 but you read the file into a memory stream and pass that memory stream as the argument.

        MemoryStream ms = new MemoryStream();
        FileStream stream = new FileStream("picture.png", FileMode.Open, FileAccess.Read);
        ms.SetLength(stream.Length);
        stream.Read(ms.GetBuffer(), 0, (int)stream.Length);

        ms.Flush();
        stream.Close();

        Image i = new Image();
        BitmapImage src = new BitmapImage();
        src.BeginInit();
        src.StreamSource = ms;
        src.EndInit();
        i.Source = src;
        i.Stretch = Stretch.Uniform;
        panel.Children.Add(i);

Now you are able to modify the file on the system, if that is something you require.

User · Answer

In code to load resource in the executing assembly where my image  Freq png  was in the folder  Icons  and defined as  Resource            this Icon   new BitmapImage new Uri   pack   application                       Assembly GetExecutingAssembly   GetName   Name                   component                    Icons Freq png   UriKind Absolute       I also made a function if anybody would like it          lt summary gt      Load a resource WPF-BitmapImage  png  bmp       from embedded resource defined as  Resource  not as  Embedded resource        lt  summary gt       lt param name  pathInApplication  gt Path without starting slash lt  param gt       lt param name  assembly  gt Usually  Assembly GetExecutingAssembly     If not mentionned  I will use the calling assembly lt  param gt       lt returns gt  lt  returns gt  public static BitmapImage LoadBitmapFromResource string pathInApplication  Assembly assembly   null        if  assembly    null                assembly   Assembly GetCallingAssembly               if  pathInApplication 0                        pathInApplication   pathInApplication Substring 1             return new BitmapImage new Uri   pack   application         assembly GetName   Name     component     pathInApplication  UriKind Absolute         Usage           this Icon   ResourceHelper LoadBitmapFromResource  Icons Freq png

User · Answer

Here is the extension method to load an image from URI   public static BitmapImage GetBitmapImage      this Uri imageAbsolutePath      BitmapCacheOption bitmapCacheOption   BitmapCacheOption Default        BitmapImage image   new BitmapImage        image BeginInit        image CacheOption   bitmapCacheOption      image UriSource   imageAbsolutePath      image EndInit         return image      Sample of use   Uri  imageUri   new Uri imageAbsolutePath   ImageXamlElement Source    imageUri GetBitmapImage BitmapCacheOption OnLoad     Simple as that

User · Answer

You could try attaching handlers to various events of BitmapImage    DecodeFailed DownloadFailed DownloadCompleted   They might tell you a little about what s going on  as far as the image is concerned

User · Answer

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

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