Could not load file or assembly 'Xceed.Wpf.Toolkit

I know that this is a very old question but I happened to run across this exact error not too long ago. If your visual studio application uses two projects or a project that references another project, I would check to make sure that BOTH projects have the extended toolkit installed.

Right click on both your projects and click, "Manage NuGet Packages" and then browse on the left hand side of the dialogue to "Installed Packages". If you do not see extended toolkit on both projects then you can use the manager to search online and install them for you.

My issue was that I only had the extended toolkit installed on one project not both.

Hopefully this helps someone out in the future.

I am a fan of this approach. You can register an event on the AppDomain for the AssemblyResolve event, which catches when an assembly cannot be loaded.

It looks like this:

// using System.Reflection and System.IO

AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(CurrentDomain_AssemblyResolve);

private Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args )
{
    if (args.Name.ToUpper().StartsWith("XCEED.WPF"))
    {
       string asmLocation = Assembly.GetExecutingAssembly().Location;

       string asmName = args.Name.Substring(0, args.Name.IndexOf(','));
       string filename = Path.Combine( asmLocation, asmName );

       if (File.Exists(filename)) return Assembly.LoadFrom(filename);
    }
}

You can make it a little more complete than this, but you get the idea...

Although this has probably been solved, a common reason is failure to add the Xceed.Wpf.Toolkit dll to your entry point project. You probably added it to one of your class libary projects and set its "Copy Local" attribute to true. A reference to this dll also has to be added to your main project which contains your App.xaml.cs with its "Copy Local" attribute set to true.

I am surprised Visual Studio 2013 does not handle this automatically.

So, I found a new and better solution to this question of mine from 2014.

Today I ran into the same problem where loading a WPF control from an assembly would throw an XamlParseException, except this time it was with a WPF control library assembly that I had created.

I tried moving the DLL into the same folder as the EXE, and as before this solved the problem.

After some searching, I found this question on the telerik.com forums: http://www.telerik.com/forums/xamlparseexception-could-not-load-file-or-assembly

It turns out if you simply give the control a name, by adding a x:Name attribute, this will add a reference to the control in the code-behind and for some reason resolves the issue with loading the assembly.

  <!--This causes a XamlParseException -->
  <mylib:MyCustomControl />

  <!-- This works -->
  <mylib:MyCustomControl x:Name="foobar"/>