error migrating vb.net program from vs2019 to vs2026

Question

Designer could not be shown since none of the classes can be designed.

|| |Instances of this error (1)| || ||

1.		Hide Call Stack
1.		Hide Call Stack

at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.EnsureDocument(IDesignerSerializationManager manager) at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager) at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager) at System.ComponentModel.Design.Serialization.BasicDesignerLoader.BeginLoad(IDesignerLoaderHost host)

Answer 1

This designer error usually means the project is not building cleanly after the migration, or the form class is no longer in a state that the Windows Forms Designer can load.

Use this sequence:

1. Check the full project Error List and fix all compile errors first. The designer can fail to open any form when the project has unresolved build errors.
2. Verify the project target framework in Solution Explorer > right-click project > Properties. For migrated Visual Basic Windows Forms projects, confirm it targets the intended framework, such as .NET Framework 4.8, if that is what the project requires.
3. Clean stale build output:
   • Build > Clean Solution
   • Delete the bin and obj folders
   • Rebuild the solution
4. If the project uses settings-related attributes and the migration introduced errors such as System.Configuration.ApplicationScopedSettingAttribute not being found, add the missing package/reference and then rebuild.
5. If the form still does not open, check whether the form class is the first class in the file. The designer requires the first class in the file to be the one it loads.
6. Confirm the form inherits from a class that can be visually designed. If the class does not inherit from a designable base class, Visual Studio cannot open it in the designer.
7. If the file cannot be designed, open it in Code view instead: in Solution Explorer, right-click the file and choose View Code.
8. If the issue started after the Visual Studio upgrade and persists after rebuild, run Repair from Visual Studio Installer > More > Repair.

Relevant causes for the specific call stack shown:

• CodeDomDesignerLoader.PerformLoad can fail when the language does not provide a parser for the file type.
• It also throws when the class can be designed but is not the first class in the file, or when none of the classes in the file can be designed.

If the migrated project also shows missing type errors, resolve those first before reopening the designer.

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• Windows Forms Designer error page
• CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager) Method
• How can i solve this error - Microsoft Q&A When trying to open a VS19 project with VS22, the Designer gives this error
• updated and will not show designers - Microsoft Q&A I updated and now none of my design forms will display. One error message is The designer could not be shown for this file because none of he classes within it can be designed. Another says "The type 'System.Configuration.ApplicationScoped SettingAttribute' could not be found.