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We are developing a VSTO Document-level customisation for MS word. We need to access the document from a background thread so that we do not stop the UI refreshing.

This works fine for properties such as Sections / Table etc on DocumentBase.

When trying to access CustomDocumentProperties or BuiltInDocumentProperties the following exception is received

Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.Office.Core.DocumentProperties'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{2DF8D04D-5BFA-101B-BDE5-00AA0044DE52}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

Is it possible to access these properties from a background thread?

Thanks

user1562637
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1 Answers1

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First of all, you should not access the Office object model from background threads because Office applications using the single threaded apartment model.

Use the late-binding technology for accessing the document properties, see the Type.InvokeMember method for more information. For example:

object properties = workBk.GetType().InvokeMember("CustomDocumentProperties", BindingFlags.Default | BindingFlags.GetProperty, null, workBk, null);

object property = properties.GetType().InvokeMember("Item", BindingFlags.Default | BindingFlags.GetProperty, null, properties, new object[] { propertyIndex });

object propertyValue = property.GetType().InvokeMember("Value", BindingFlags.Default | BindingFlags.GetProperty, null, propertyWrapper.Object, null);

Also you may take a look at the similar pages:

Set custom document properties with Word interop

Accessing Excel Custom Document Properties programatically

Community
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Eugene Astafiev
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  • Thanks, this helped a lot. For anyone else looking it also appears that CustomDocumentProperties returns a dynamic when accessed from a different thread and hence the cast exception – user1562637 Jul 20 '15 at 07:15
  • There is a less verbose solution in the last link in this answer, `dynamic`. As far as I can tell they are functionally equivalent, and the code is this answer was only relevant prior to C# 4.0. Also @Eugene, I think your first sentence is missing a 'not'. – Chris Mar 08 '17 at 15:11
  • Right, missed a 'not' part in the first sentence. – Eugene Astafiev Mar 08 '17 at 16:01