I added the xmlns attribute to my window and things worked just fine. I got my IntegerUpDown in there and all was well. Close VS2015 Community and open it again, and the control is invisible. It still builds correctly and can be edited but it's just a transparent frame in the editor.
Fine, I can work with this. Now I wanted to use a DecimalUpDown, but that completely breaks, I get an exception, see attached image. The tag that was added is just empty. Other controls work but are as invisible as IntegerUpDown. DoubleUpDown breaks the same way DecimalUpDown does.
I've uninstalled and reinstalled without any difference, what is going on here? My application works fine outside of this, but I'm very new to Visual Studio so I might be missing something obvious.
Comments: ** Comment from web user: BOLL **
OK, I finally found out why it breaks.
I get this issue if I add a second platform in the Configuration Manager, then the controls become invisible and some of them just generate the above mentioned exceptions and errors.
I had added a separate x64 platform because I use 64-bit .DLLs. Now I instead edit the build settings in Properties and set x64 there and things work again. I discovered this by experimenting with a new project.
So to recreate the error do the following:
1. Start a new Visual C# > Windows > Classic Desktop > WPF Application
* With the project open, click down the dropdown at the top that says "Debug", open the "Configuration Manager".
* Click the "Any CPU" drop-down and pick <New...>, pick a platform and press OK, I used x64 here.
* Open your xaml and drag any control from WpfToolkit into the editor. It should either be invisible or give errors.