topic Re: Object reference not set to an instance of an object. in ArcObjects SDK Questions

Object reference not set to an instance of an object.

Gautham_SChejarla — Tue, 08 Feb 2011 23:40:49 GMT

Hi All,

I am using C# for ArcObjects desktop. Kindly clarify me on the below to declarations

1.   IApplicatin app = IMxDocument.doc as IApplication;
      ----
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throws an exception (NUllReferenceException) when i use
app.OpenDocument(filename)------ where filename is a string in the openFileDialog1

2.    IApplication app = (IMxDocument.doc as IDocument).Parent
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This does not throw an exception. My doubt is why does the first option throw an error while second option does not even though both IApplication & IDocument.Parent both refer to Application.

Thanks a lot in advance...!

Re: Object reference not set to an instance of an object.

SteveFang — Wed, 09 Feb 2011 18:31:31 GMT

IMxDocument is not the same as IApplication, they are in two different co-classes. The document is derived from the application so you can't cast a document as application but you can cast the parent of the document as application because the parent of a document is the application. Hopefully that explanation helps.

Re: Object reference not set to an instance of an object.

Gautham_SChejarla — Thu, 10 Feb 2011 16:16:36 GMT

IMxDocument is not the same as IApplication, they are in two different co-classes. The document is derived from the application so you can't cast a document as application but you can cast the parent of the document as application because the parent of a document is the application. Hopefully that explanation helps.

Thanks a lot....