CODEWITHSUNDEEP
winformsvisual-studio-2010
estanford
estanford

Reputation: 1312

Trouble finding source of a designer exception in VS2010

When loading the mainform of a WinForms app I'm working on, I encountered a familiar exception: a "To prevent possible data loss before loading the designer, the following errors must be resolved" error. The stacktrace is as follows: 

Object reference not set to an instance of an object.    

Instances of this error (4)  

1.   Hide Call Stack 

at System.ComponentModel.ReflectPropertyDescriptor.SetValue(Object component, Object value)
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkPropertyDescriptor.SetValue(Object component, Object value)
at System.Windows.Forms.Design.ControlDesigner.CanResetSizePropertyDescriptor.SetValue(Object component, Object value)
at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializePropertyAssignStatement(IDesignerSerializationManager manager, CodeAssignStatement statement, CodePropertyReferenceExpression propertyReferenceEx, Boolean reportError)
at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeAssignStatement(IDesignerSerializationManager manager, CodeAssignStatement statement)
at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeStatement(IDesignerSerializationManager manager, CodeStatement statement)

I know what's causing this error -- there are four lines buried somewhere in the MainForm that make reference to an image object that doesn't exist at design time. I even have an idea of how to fix the error, thanks to this post at MSDN. The trouble is, I can't find the lines from which the exception is thrown. Normally I would navigate to the exception using the Error List window, but it says that there are zero errors. Any ideas as to how I can locate the offending lines?

Upvotes: 2

Views: 2957

Answers (1)

Rebecca Scott
Rebecca Scott

Reputation: 2431

I usually find that this relates to a user control hosted on the form that relies on a DI container or similar, but as you say it is sometimes difficult to determine the source from the call stack the designer provides. If you're hosting a lot of controls, to figure out which controls are causing the issue without diving into each one you could:

  1. Make a list of the user controls that are directly hosted on the form, then
  2. Create a new temporary form, then
  3. Drop each user control in your list onto the form to see which one kills the designer

Upvotes: 2

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