wpf - How to Set Image Resource URI from Code-Behind

Question

I am trying to embed a PNG graphic into a DLL and load it into an Image control as a BitmapImage. However, WPF keeps throwing an exception saying that the resource cannot be found.

First, some minimal sample code and the steps to reproduce the problem:

• Create a WPF project named ImageResTest with an empty main window (you can set the default namespace to ImageResTest). The code-behind file of the main window should look like this:

  using System;
  using System.Windows;
  using System.Windows.Controls;
  
  namespace ImageResTest
  {
      public partial class Window1 : Window
      {
          public Window1()
          {
              InitializeComponent();
  
              var obj = new MyData.SomeStuff.MyClass();
  
              this.Content = obj.Img;
          }
      }
  }
  

• Create a class library named ImageResTestLib (you can set the default namespace to ImageResTest, as above, so everything discussed here is in the same root namespace).

• Add references from ImageResTestLib to PresentationCore, PresentationFramework, System.Xaml and WindowsBase.
• Add a reference from ImageResTest to ImageResTestLib.
• Inside ImageResTestLib, add the folder hierarchy MyData/SomeStuff/Resources.

• In the SomeStuff folder, add the following file MyClass.cs:

  using System;
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Media;
  using System.Windows.Media.Imaging;
  
  namespace ImageResTest.MyData.SomeStuff
  {
      public class MyClass
      {
          public MyClass()
          {
              img = new Image();
              {
                  var bmp = new BitmapImage();
                  bmp.BeginInit();
                  bmp.UriSource = new Uri(@"/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png", UriKind.RelativeOrAbsolute);
                  bmp.EndInit();
  
                  img.Source = bmp;
                  img.Width = bmp.PixelWidth;
              }
          }
  
          private Image img;
  
          public Image Img {
              get {
                  return img;
              }
          }
      }
  }
  

• In the Resources folder, add a PNG file named Img.png and set its build action to Resource (as suggested, for example, here).

So far, so good - launching this application should create a window which instantiates MyClass and retrieves an Image created by that MyClass instance. That image should have been filled with a BitmapImage whose data was loaded from the graphic included as a resource.

Unfortunately, there seems to be something wrong with the resource URI. The documentation on MSDN has not helped so far.

I have tried the following variants of resource URIs:

• The form depicted in the code sample above - /AssemblyName;component/Path/Filename - was suggested here and here, but a DirectoryNotFoundException is thrown, saying that a part of the path C:ImageResTestLib;componentMyDataSomeStuffResourcesImg.png was not found.
• pack://application:,,,/MyData/SomeStuff/Resources/Img.png was suggested here, here, here and here, but throws an IOException saying that the resource mydata/somestuff/resources/img.png could not be found.
• pack://application:,,,/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png was also suggested here, as well as here, but throws a FileNotFoundException saying that ImageResTestLib, Culture=neutral or one of its dependencies was not found.
• Resources/Img.png (relative from the code file) was implied here and here, but throws a DirectoryNotFoundException saying that C:UsersmyusernameDocumentsTestDOTNETWPFTestImageResTestinDebugResourcesImg.png was not found.
• MyData/SomeStuff/Resources/Img.png (relative to the project), also as implied here, behaves analogously to the previous one.

As none of these would work, I tried the following workaround based on a ResourceDictionary:

• Add a WPF resource dictionary named MyClassResources.xaml in the SomeStuff folder.
• In that resource dictioanry, add a BitmapImage resource with the key img.

• Change the contents of MyClass.cs like this:

  using System;
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Media;
  using System.Windows.Media.Imaging;
  
  namespace ImageResTest.MyData.SomeStuff
  {
      public class MyClass
      {
          public MyClass()
          {
              ResourceDictionary dict = new ResourceDictionary();
              dict.Source = new Uri("/ImgResTestLib;component/MyData/SomeStuff/MyClassResources.xaml", UriKind.RelativeOrAbsolute);
  
              img = new Image();
              {
                  var bmp = (BitmapImage)dict["img"];
  
                  img.Source = bmp;
                  img.Width = bmp.PixelWidth;
              }
          }
  
          private Image img;
  
          public Image Img {
              get {
                  return img;
              }
          }
      }
  }
  

Now, the resource dictionary can be loaded from the indicated URI (when removing the contents of the resource dictionary, loading completes successfully). However, the PNG graphics are still not found when using a path like /ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png.

What am I doing wrong and how can I load the respective resources (if possible, without the extra resource dictionary)?

---

EDIT: Some more information:

• I am using a German Windows 7 x64
• .NET 4.0 Client is set as the target framework
• Just to make sure, I have tried building and running this both from within Visual Studio 2010 and SharpDevelop 4.3.3; both times resulting in the same exception.

The stacktrace of the FileNotFoundException I am getting based on Ian's code is as follows:

System.Windows.Markup.XamlParseException: Zeilennummer "3" und Zeilenposition "2" von "Durch den Aufruf des Konstruktors für Typ "ImageResTest.Window1", der den angegebenen Bindungseinschr?nkungen entspricht, wurde eine Ausnahme ausgel?st.". ---> System.IO.FileNotFoundException: Die Datei oder Assembly "ImageResTestLib, Culture=neutral" oder eine Abh?ngigkeit davon wurde nicht gefunden. Das System kann die angegebene Datei nicht finden.
   bei System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   bei System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   bei System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   bei System.Reflection.Assembly.Load(AssemblyName assemblyRef)
   bei System.Windows.Navigation.BaseUriHelper.GetLoadedAssembly(String assemblyName, String assemblyVersion, String assemblyKey)
   bei MS.Internal.AppModel.ResourceContainer.GetResourceManagerWrapper(Uri uri, String& partName, Boolean& isContentFile)
   bei MS.Internal.AppModel.ResourceContainer.GetPartCore(Uri uri)
   bei System.IO.Packaging.Package.GetPartHelper(Uri partUri)
   bei System.IO.Packaging.Package.GetPart(Uri partUri)
   bei System.IO.Packaging.PackWebResponse.CachedResponse.GetResponseStream()
   bei System.IO.Packaging.PackWebResponse.GetResponseStream()
   bei System.IO.Packaging.PackWebResponse.get_ContentType()
   bei System.Windows.Media.Imaging.BitmapDecoder.SetupDecoderFromUriOrStream(Uri uri, Stream stream, BitmapCacheOption cacheOption, Guid& clsId, Boolean& isOriginalWritable, Stream& uriStream, UnmanagedMemoryStream& unmanagedMemoryStream, SafeFileHandle& safeFilehandle)
   bei System.Windows.Media.Imaging.BitmapDecoder.CreateFromUriOrStream(Uri baseUri, Uri uri, Stream stream, BitmapCreateOptions createOptions, BitmapCacheOption cacheOption, RequestCachePolicy uriCachePolicy, Boolean insertInDecoderCache)
   bei System.Windows.Media.Imaging.BitmapImage.FinalizeCreation()
   bei System.Windows.Media.Imaging.BitmapImage.EndInit()
   bei ImageResTest.MyData.SomeStuff.MyClass..ctor(Uri baseUri) in C:UsersusernameDocumentsTestDOTNETWPFTestImgResTestLibMyDataSomeStuffMyClass.cs:Zeile 36.
   bei ImageResTest.Window1..ctor() in c:UsersusernameDocumentsTestDOTNETWPFTestImageResTestWindow1.xaml.cs:Zeile 17.
   --- End of inner exception stack trace ---
   bei System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   bei System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
   bei System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
   bei System.Windows.Application.LoadBamlStreamWithSyncInfo(Stream stream, ParserContext pc)
   bei System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties)
   bei System.Windows.Application.DoStartup()
   bei System.Win

Answer 1

Part of the problem is that WPF has no context with which to resolve that URL. It's a relative URL, and typically, it would be resolved relative to the base URI of the XAML content in which it's used. If I use exactly the same URL you start with in this code:

public MainWindow()
{
    InitializeComponent();

    var img = new Image();
    Content = img;
    var bmp = new BitmapImage();
    bmp.BeginInit();
    bmp.UriSource = new Uri(@"/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png", UriKind.RelativeOrAbsolute);
    bmp.EndInit();

    img.Source = bmp;
    img.Width = bmp.PixelWidth;
}

then it works. That's in the codebehind for MainWindow, obviously.

With one tiny change, moving this line:

Content = img;

to the end, then I get the same DirectoryNotFoundException as you.

WPF tries to resolve that URI to an actual resource at the point at which you assign the BitmapImage as the Source property of that Image. My first example works because the Image is in the visual tree, and so it picks up the base URI of MainWindow.xaml, and resolves that resource URI relative to that base URI.

If you really need to create the Image before it gets associated with a visual tree, you've got various options. You could actually set the base URI on the image:

img.SetValue(BaseUriHelper.BaseUriProperty, baseUri);

However, that's kind of weird. It's easier just to construct an absolute URI, e.g.:

bmp.UriSource = new Uri(
    baseUri,
    @"/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png");

Both of these of course presume that you know what the base URI is. You can find that out by asking in your MainWindow constructor:

public MainWindow()
{
    InitializeComponent();

    var baseUri = BaseUriHelper.GetBaseUri(this);
    ...

In your case, that'll be: pack://application:,,,/ImageResTest;component/mainwindow.xaml

This in turn makes it clear what the resolved URI should be: pack://application:,,,/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png

Interestingly, you say you try that and get an error. Well I'm trying that exact URI, and I'm not getting an error. Just to be clear, here's my modified version of your MyClass constructor:

public MyClass(Uri baseUri)
{
    img = new Image();
    var bmp = new BitmapImage();
    bmp.BeginInit();
    bmp.UriSource = new Uri(baseUri, @"/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png");
    bmp.EndInit();

    img.Source = bmp;
    img.Width = bmp.PixelWidth;
}

and here's my MainWindow constructor:

public MainWindow()
{
    InitializeComponent();

    var obj = new MyData.SomeStuff.MyClass(BaseUriHelper.GetBaseUri(this));

    this.Content = obj.Img;
}

This works for me, having followed your instructions. If I understand you correctly, you're seeing a FileNotFoundException when you do this. This makes me wonder if your instructions have omitted something. E.g., I'd expect to see this error if ImageResTestLib was strongly named. (If you want to refer to a resource in a strongly-named library, you need a fully qualified assembly display name before the ;component part.)

Another option would be to use Application.GetResourceStream, along with the BitmapImage.StreamSource property. But again, this is going to need a working URL, so you're likely going to hit the same problem as you had before. Once you work out what's different in your project that's stopping pack://application:,,,/ImageResTestLib;component/MyData/SomeStuff/Resources/Img.png from working, then the basic approach you already have should be fine.