I'm using Visual C# 2008 Express. This is the first time I've had this error in years, the last time I had it was around the time I started programming.
I have no idea what it actually means or why it suddenly came up, it seems rather ambiguous for what the error message says. All I know is that throughout my app, I inherit a lot of the main windows from a ThemedWindow class I came up with to give them a custom appearance, there are no errors in that code and everything was working 100% perfect 20 minutes ago.
The error in full:
Warning 12 The designer could not be shown for this file because none of the classes within it can be designed. The designer inspected the following classes in the file:
InheritingWindow --- The base class 'ThemedWindow' could not be loaded. Ensure the assembly has been referenced and that all projects have been built. 0 0
These problems were caused by an unfortunate bug in Visual Studio. I had other errors (not warnings) in some code, even though nothing else directly depended upon it, which played a part in this whole situation.
I could be wrong in explaining it but here's what I think went wrong: for some reason (bug), it totally forgot about unchanged objects it had already compiled before, gave me the actual errors I had in my code, and a bunch of other warnings because it wouldn't go past that point. I couldn't get into the designer for forms that depended upon
ThemedWindow because I'm guessing
ThemedWindow hadn't recompiled before these errors occurred.
Once I commented out the erroneous code as a quick fix and rebuilt the solution, everything compiled successfully.