Question

I have created a custom data grid control. I dragged it on windows form and set its properties like column and all & ran the project. It built successfully and I am able to view the grid control on the form.

Now if i try to view that form in designer, I am getting following error..

Object reference not set to an instance of an object.     




Instances of this error (1)  

1.   Hide Call Stack 

at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.GetMemberTargetObject(XmlElementData xmlElementData, String& member)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.CreateAssignStatement(XmlElementData xmlElement)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.XmlElementData.get_CodeDomElement()
at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.EndElement(String prefix, String name, String urn)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.Parse(XmlReader reader)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.XML.CodeDomXmlProcessor.ParseXml(String xmlStream, CodeStatementCollection statementCollection, String fileName, String methodName)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomParser.OnMethodPopulateStatements(Object sender, EventArgs e)
at System.CodeDom.CodeMemberMethod.get_Statements()
at System.ComponentModel.Design.Serialization.TypeCodeDomSerializer.Deserialize(IDesignerSerializationManager manager, CodeTypeDeclaration declaration)
at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.DeferredLoadHandler.Microsoft.VisualStudio.TextManager.Interop.IVsTextBufferDataEvents.OnLoadCompleted(Int32 fReload) 

If I ignore the exception, form appears blank with no sign of grid control on it. However I can see the code for the grid in the designer file.

Any pointer on this would be a great help.

I have customized grid for my custom requirements like I have added custom text box n all. I have defined 3 constructors

public GridControl() 
public GridControl(IContainer container) 
protected GridControl(SerializationInfo info, StreamingContext context)

Answer 1

I have this problem all the time…it sucks.

[Ramble(on)]

Here is what I think I know:

1. When designing place the control on a form. Build and refresh often..this will let you know what change caused the designer to barf.
2. Close visual studio all the way an re-open….I cannot tell you how many times I have chased a designer error that was the designer being “stuck”.
3. It is very important that you understand : The designer is really, really stupid…like bag of rocks stupid.

4. Any public fields or properties of custom object types will almost always cause designer confusion*. I find the following attributes will clear up most of these problems:

   [Browsable(false)]

   [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]

5. Public fields or properties without a default constructor will always cause designer confusion. When you drop a user control on a form the designer effectively creates the control..so any public object needs a clear creation path. I have found that the easiest way around this (read hack) is keeping the non-trivial custom classes private and expose public properties as a facade.

— Did I say restart visual studio because sometimes the designer is “stuck” on an error that doesn’t exist ?..I hope I did.

[Ramble(off)]

I hope some of this helps..

*designer confusion: Instead of showing your controls the designer shows you a useless error message that might or might not include the dire warning that it is protecting you from code loss…blah, blah.