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I have recently been getting an error in the Windows Forms designer of VS2010SP1 when using inherited UserControls.

The error is

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: DebugPanel --- The base class 'UI.Panels.PanelBase' could not be loaded. Ensure the assembly has been referenced and that all projects have been built.

PanelBase is a UserControl that is defined in the same class library as DebugPanel that also implements an interface IPanel (which is in turn defined in the same class library). IPanel implements an interface IBaseItem that is defined in a different class library.

So we have

DebugPanel            (Library UI.Shared2)
- PanelBase           (Library UI.Shared2)
    - UserControl     (System.Windows.Forms - .NET4)
    - IPanel          (Library UI.Shared2)
        - IBaseItem   (Library Net.Common)

PanelBase is designable correctly, the project all builds correctly and works but when I try and design any inherited control the designer fails. This is not limited to the DebugPanel control, but any control inheriting from PanelBase... I've also seen the issue with other controls that I use that have similar inheritance hierarchies.

I can generally resolve the problem temporarily by cleaning the library UI.Shared2, closing VS and then opening it again, rebuilding the solution and opening the designer. This will then work for a short while and then start to fail again.

Does anyone have any suggestions that can resolve this issue permanently without resorting to restarting VS?

Edit: I am targeting the full version of .NET 4 with all libraries.

participant
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Anthony
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  • Try targeting the full version of .NET instead of the Client Profile. – Hans Passant Oct 14 '11 at 09:28
  • Apologies - I forgot to add that I am targeting the full version of .NET4. Initially I was only targeting the Client Profile but I thought I'd give the full version a go! – Anthony Oct 14 '11 at 09:29
  • I had similar problem opening few of my forms in VS2010, but I put it down to some 3rd party components we use from .net 1.1 up in the base classes. My situation was so bad that it shows red error messages every time i try to open it in designer and even it refuses to save the hand written code.Our management decided to not renew licenses of that 3rd party ( .net 4 version). So I end up wrapping those controls in a .net 4.0 wrapper and then use those controls in the base components now everything works fine :). I dont know if you are in same situation. – Surjit Samra Oct 15 '11 at 03:15
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    @SSamra, that is an interesting suggestion - one that I wouldn't have thought of (since surely it should be backwards compatible!) but could potentially be the source of the problem as we do indeed use a 3rd party library that targets .NET 2 (from memory). I'll give that a go, thanks. – Anthony Oct 24 '11 at 10:37

8 Answers8

23

I had the same issue. I had a Form object/base object I was inheriting from, and all of a sudden I see this message for all Forms that were inheriting from the Base.

I tried to backtrack and figure out what changed recently and remembered I set my project Platform Target from Any CPU to x64. I changed it back to Any CPU and the problem got resolved, and then setting it back again to x64 still kept the problem fixed.

This was on VS 2013, by the way.

Avazee
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  • Messing with targets is what did it for me as well. This fix works in VS 2015 in my case. – KatDevsGames Sep 21 '15 at 18:26
  • This fixed it for me as well. For some reason, the windows forms projects were set to x64. I changed them to AnyCPU, cleaned and built, and it was fixed. Thanks! – komma8.komma1 Sep 06 '16 at 21:32
  • Same here in VS2015. I also forgot that I had switched. Below is a reference to the problem, which explains that the Form Designer requires a compiled assembly in order to display an inherited form but that VS itself is a 32-bit process, and the solution is to use AnyCPU. I haven't tried but is it not possible to move the base form class into an AnyCPU dll and reference it in the x64 one? https://support.microsoft.com/en-ca/kb/967050 – Craig Silver Oct 15 '16 at 21:21
  • Solved for me on VS2015. – emerson.marini Apr 03 '19 at 10:55
  • Switched from Release to Debug and then the other way round, and it worked. Thanks! – Lev Leontev Sep 24 '21 at 12:57
  • Solved for me on VS2022 – tedebus Aug 31 '23 at 09:47
8

I've been having this issue a lot recently and found an easy and fast workaround and decided to share it (works for me on VS 2012).

When you have a Form like this:

public partial class MyForm : MyBaseForm

and the designer fails to design MyBaseForm saying the base class 'System.object' cannot be designed, all I have to do is to remove : MyBaseForm and revert (Backspace > Ctrl + Z). The designer will come to its senses then.

public partial class MyForm : MyBaseForm // The designer has trouble with this
public partial class MyForm              // Force an error
public partial class MyForm : MyBaseForm // Revert back, the designer should now work again

All that's left to do now, is to wait for Microsoft to fix that annoying bug.

Nolonar
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  • Bug still exists in VS 2013, but this hack still seems to work. – Daniel Jul 25 '14 at 19:10
  • I tried moving MyBaseForm in to a separate project, as suggested by jmoreno and it did NOT fix the issue. This simple trick did, however. – sapbucket Jul 24 '15 at 17:34
  • Nice try, but in my case the designer did not come back to its senses. It showed the very same error. – Obi Wan Jul 05 '17 at 19:23
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    Bug still in VS 2019, combing through several of my referenced projects and setting them to compile with AnyCPU eventually worked for me – bkwdesign Oct 06 '21 at 14:47
7

I would suggest putting your base class in a separate project. As you obviously know, the problem is that VS is losing track of some meta information, which you can get it to find by quitting and rebuilding. If the base class is in a separate project, a clean/rebuild is more likely to bring it back up to date.

RJFalconer
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jmoreno
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  • Hmmm, I might give that a go with a branch of the code and a limited subset of the projects - unfortunately the component is used in a large number of other projects so it would be a bit of an administrative nightmare to ensure they have all been updated correctly. Although I'm not sure this should be a "solution", it should just work! – Anthony Oct 24 '11 at 10:35
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    Just a follow up... I didn't quite follow this suggestion but it is the closest to my eventual "solution". I moved the new classes (DebugPanel on my hierarchy above) in to a separate project and so far everything seems to work. I'm not happy at having to do this and I feel it is a bug in the Forms Designer but oh well... – Anthony Nov 11 '11 at 12:03
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    @Anthony: Oh, there's no question about it being a bug in VS. But other than reporting it, http://connect.microsoft.com/VisualStudio, there's nothing to do but live with it or work around it. – jmoreno Nov 11 '11 at 17:56
  • I might have a solution that does not require moving the project. I had the same problem and my solution was to 1) Close or deselect the inheriting forms designer tab 2) Close VS 3) Delete obj folder 4) Restart VS and Rebuild project. It worked for me! – AndrewBenjamin Oct 07 '15 at 16:18
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    Six years later this is still a bug. Great work, Microsoft. – Obi Wan May 16 '17 at 20:51
  • I am having this issue again and I have some feedback on your answer: My base class is in a separate project. I quote and rebuilt the solution and the error still happens. So your answer failed to solve my issue. – Obi Wan Jul 05 '17 at 19:04
  • @ObiWan: it's a bug in VS, my answer is not a solution, it is simply one workaround that **may** reduce the frequency of encountering the bug. There is no real answer/solution other than MS finding the problem and fixing it or coincidentally fixing it. All of the answers to this questions are simply things that may, under some circumstances, cause the bug not to be hit or cause VS to overwrite the bad data that the bug produces or are different problems with similar symptoms. Good luck with finding a workaround that works for you. – jmoreno Jul 05 '17 at 23:14
  • I appreciate your response. I did some more research, and according to at least two different Microsoft resources, this is not a bug but is by design. I strongly disagree with this being "by design", but that is what they are saying. I have a more complex situation in that I have a Form A which has a Base Class of Form B. Form B has a base class of Form C. And Form C is just a form with the standard base class. For me, Forms A and B refuse to show at all and I have not been able to get them to show no matter what I do. But hey, its "by design" so its all good, right? – Obi Wan Jul 07 '17 at 13:42
  • 11 years later vs2022 and this is Still a problem. It's a wonder any software works. I predict a software apocalypse. – dcarl661 Sep 26 '22 at 18:55
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  1. Clean Project (not sure if this is necessary)
  2. Set build to Release
  3. Rebuild Project

The forms designer will not rebuild the forms that you manually edited if you build the project in Debug mode apparently.

sonofsmog
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1

I also have found that when you are trying to design a form that may have referenced libraries that are already in use, then it fails to design.

I often run several Visual Studio instances. If I leave an instance of VS running a program in debug mode, and that program shares a library with the instance of Visual Studio in which I am trying to design, then I run into this problem. It also can be as simple as the DLL that the designer references is in use.

Once you close the program that is locking those library files then the designed returns to normal.

jonsca
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Andrew Kanieski
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1

To add to this extensive list of issues that could cause this error, it seems that inheriting from a generic type or abstract class can screw the designer.

bakester14
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  • Agreed, in my case it was a generic subclass of a view that screwed the designer, in addition must put ppoject settings as AnyCPU. Combining these 2 fixed most of my problems. – Alexis Martial Apr 26 '23 at 12:10
1

I solved this issue renaming all my forms and user controls and than renaming them back again...

For Example:

My user control... enter image description here

Right click on.., enter image description here

Renaming... enter image description here

And then do the same whit the original name all works now...

Payedimaunt
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0

I had this bug with VS2015, tried clean/rebuild steps, build in release didn't work.

I put the base control in another project and the designer complained that there wasn't a constructor for it. I had a constructor with 2 arguments, but no empty one. I added an empty constructor and the designer worked. I then moved the base control back in it's original location with the derived controls, and the designer bug came back.

I gave up and just put the base control in a "VsBug" project, seems to be happy...

S Bowyer
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