Visual Designer cannot load this class

The other reason something might be null is because you hadn't yet assigned anything to it.

Is there a way to determine what needs to not be null?  The error says Value cannot be null.  My UserControl has a UltraLabel and a UltraMaskedEditor.  I don't have a Value property.

Look for an assignment to a parameter named "value".  Second: look in the .log file at /.metadata/.log.  There might be more to the message, or perhaps a second message there that may indicate a primary problem.

I am running into this again and have tried everything I can to no avail.

This is the information from the .log file:

!ENTRY com.openedge.pdt.core 4 20001 2012-04-17 17:09:54.970
!MESSAGE Root component of designer host was not created.
at OpenEdge.Designer.DesignCanvas.Commands.DeSerializeCodeDomMessage.Execute()
at OpenEdge.Designer.Comm.EditorServer.handleCallback(IIPCClient targetClient, IIPCInputMessage callbackMsg)

!ENTRY com.openedge.pdt.core 4 20001 2012-04-17 17:09:54.970
!MESSAGE Root component of designer host was not created.
at OpenEdge.Designer.DesignCanvas.OEDesignSurfaceManager.CreateVisualEditor(VisualEditorManager editorManager, DesignSurfaceCreationContext createContext)
at OpenEdge.Designer.DesignCanvas.Commands.DeSerializeCodeDomMessage.CreateEditor()

!ENTRY com.openedge.pdt.ve 4 20001 2012-04-17 17:09:54.970
!MESSAGE An internal error occured
!STACK 0
java.lang.reflect.InvocationTargetException: An exception occurred loading the design canvas: Root component of designer host was not created.
at com.openedge.pdt.ve.editor.VisualDesignerFormLoader.run(VisualDesignerFormLoader.java:266)
at com.openedge.pdt.ve.editor.VisualDesigner.loadDesignEditor(VisualDesigner.java:803)
at com.openedge.pdt.ve.editor.VisualDesigner.doSafeLoadDesignEditor(VisualDesigner.java:765)
at com.openedge.pdt.ve.editor.VisualDesigner.doLoad(VisualDesigner.java:719)
at com.openedge.pdt.ve.editor.VisualDesigner.loadDesignEditor(VisualDesigner.java:1084)
at com.openedge.pdt.ve.editor.VisualDesigner$2.run(VisualDesigner.java:535)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)
Caused by: com.openedge.pdt.ve.comm.ClientServiceException: An exception occurred loading the design canvas: Root component of designer host was not created.
at com.openedge.pdt.ve.editor.command.output.IPCDeSerializeCodeDomMessage.execute(IPCDeSerializeCodeDomMessage.java:105)
at com.openedge.pdt.ve.editor.VisualDesignerClient.execute(VisualDesignerClient.java:350)
at com.openedge.pdt.ve.editor.VisualDesignerFormLoader.run(VisualDesignerFormLoader.java:227)
... 6 more
Root exception:
com.openedge.pdt.ve.comm.ClientServiceException: An exception occurred loading the design canvas: Root component of designer host was not created.
at com.openedge.pdt.ve.editor.command.output.IPCDeSerializeCodeDomMessage.execute(IPCDeSerializeCodeDomMessage.java:105)
at com.openedge.pdt.ve.editor.VisualDesignerClient.execute(VisualDesignerClient.java:350)
at com.openedge.pdt.ve.editor.VisualDesignerFormLoader.run(VisualDesignerFormLoader.java:227)
at com.openedge.pdt.ve.editor.VisualDesigner.loadDesignEditor(VisualDesigner.java:803)
at com.openedge.pdt.ve.editor.VisualDesigner.doSafeLoadDesignEditor(VisualDesigner.java:765)
at com.openedge.pdt.ve.editor.VisualDesigner.doLoad(VisualDesigner.java:719)
at com.openedge.pdt.ve.editor.VisualDesigner.loadDesignEditor(VisualDesigner.java:1084)
at com.openedge.pdt.ve.editor.VisualDesigner$2.run(VisualDesigner.java:535)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

Have you tried to create a simple form with only one or two control and checked if it loaded ? My previous machine setup had an isuue with designer which was due to .net version error.

Root component of designer host was not created.

This is a message from .NET.  This usually means you're inheritance is wrong.  Check the inherits phrase of your class definition to ensure it inherits from something valid, and the import statements to make sure things are kosher there as well if you are not using fully qualified type names.  Make sure that the base class name is specified with the correct case (upper/lower/mixed/whatever). Also check the .NET version to ensure you have the correct one.  Check the assemblies.xml file to make sure they point to the right versions of the .NET assemblies.

Hi Matthew,

Thank you for your reply. It got me into the process of painstakingly reviewing all code changes until I found the problem.

However,t turned out to be none of the things you mentioned below. Instead the problem was cause by an invalid handle in a GETter of a property. Therefore it was really a 4GL error. For some reason, however, the VD could not provide a proper error message.

I have asked Tech Support to create a knowledge base entry that sums up the possible causes of this error message.

-peter

I had a similar problem.

At the end it was an error in the constructor of the form that led to the crash ...

I forgot to write a check whether an object I used was valid or not ...

kind regards

Gerd

To err is human.

The problem here is that the VD does not provide *any* information so debugging such basic errors can take days instead of minutes.

We have tried to create a reproduction for Tech Support but whatever we try, we always get a proper error message *except* in our *real* code...