Skip to main content

WPF–Using the XmlnsDefinitionAttribute causes issues when loading a WPF form in an Addin

Yesterday a colleague asked me for help. She was building an addin for ESRI ArcGis and she wanted to load a WPF form and show some related data. The problem was that when loading the WPF form some of the DLL’s were searched in the Addin folder but for some of the DLL’s, .NET was looking inside the bin folder of the main application. Easy solution would be to just copy over all addin assemblies to the bin folder of ArcGis. Of course this was not what we want as it removes the advantages of the whole addin concept.

So the big question is; why are some DLL’s loaded from the correct location and others not?

Let’s have a look at the WPF form first:

In this form the services DLL was loaded correctly whereas the caliburn.micro dll(still my favorite MVVM framework Smile) was not. The difference is that the services DLL namespace is constructed using the clr-namespace syntax whereas the Caliburn.Micro namespace is constructed using an URL.

Where does this URL come from?

WPF defines a CLR attribute that is consumed by XAML processors in order to map multiple CLR namespaces to a single XAML namespace. This attribute, XmlnsDefinitionAttribute, is placed at the assembly level in the source code that produces the assembly. The WPF assembly source code uses this attribute to map the various common namespaces, such as System.Windows and System.Windows.Controls, to the http://schemas.microsoft.com/winfx/2006/xaml/presentation namespace. This prevents you from loading a lot of namespaces yourself as they can be grouped using one XAML namespace alias.

Unfortunately it was exactly this functionality that caused the Addin loader to look for assemblies at the wrong location.

How did we fix it?

By relying on the CLR behavior that the runtime first will check if an assembly is already loaded before it will try to search for it on the file system, we were able to solve the issue. Therefore inside the bootstrap logic of the addin we added the following line to explicitly load the Caliburn.Micro assembly into the appdomain:

Labels:

Popular posts from this blog

Podman– Command execution failed with exit code 125

After updating WSL on one of the developer machines, Podman failed to work. When we took a look through Podman Desktop, we noticed that Podman had stopped running and returned the following error message: Error: Command execution failed with exit code 125 Here are the steps we tried to fix the issue: We started by running podman info to get some extra details on what could be wrong: >podman info OS: windows/amd64 provider: wsl version: 5.3.1 Cannot connect to Podman. Please verify your connection to the Linux system using `podman system connection list`, or try `podman machine init` and `podman machine start` to manage a new Linux VM Error: unable to connect to Podman socket: failed to connect: dial tcp 127.0.0.1:2655: connectex: No connection could be made because the target machine actively refused it. That makes sense as the podman VM was not running. Let’s check the VM: >podman machine list NAME         ...
Read more

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.
Read more

Cleaner switch expressions with pattern matching in C#

Ever find yourself mapping multiple string values to the same result? Being a C# developer for a long time, I sometimes forget that the C# has evolved so I still dare to chain case labels or reach for a dictionary. Of course with pattern matching this is no longer necessary. With pattern matching, you can express things inline, declaratively, and with zero repetition. A small example I was working on a small script that should invoke different actions depending on the environment. As our developers were using different variations for the same environment e.g.  "tst" alongside "test" , "prd" alongside "prod" .  We asked to streamline this a long time ago, but as these things happen, we still see variations in the wild. This brought me to the following code that is a perfect example for pattern matching: The or keyword here is a logical pattern combinator , not a boolean operator. It matches if either of the specified pattern...
Read more