Excel Event Handlers

Question

Hello all, I am trying to initiate the edit of an Excel Workbook from within my applicattion and then intercept the Window Deactivate event. The opening of the Workbook works fine. But I keep getting an An unhandled exception of type 'System.InvalidCastException' occurred in interop.excel.dll Additional information: No such interface supported error during runtime for the line theExcelApp.WindowDeactivate += new Excel.AppEvents_WindowDeactivateEventHandler(ExcelWindow_Deactivate); I am using the Visual Studio IDE and it provided me with the EventHandler designation. I am at a loss. If anybody can tell me the proper way of assigning an EventHandler to an Excel Application Event, I would be much obliged.

Answer 1

Glad this helped. Don't remember exactly off hand, but I think I did a search on Google "Excel Events C#" or something equivalent. -Mike G.

Answer 2

Mike, Thank you for the information. I am curious how you managed to find the article. I spent several hours on MSDN without finding any information. Again, thank you for the info.

Answer 3

Hi rev robert, I found a useful article on your question in the Microsoft Knowledge Base Click It says if you get this exception (InvalidCastException) do the following Below is the full solution copied from this article: An unhandled exception of type 'System.InvalidCastException' occurred in interop.excel.dll Additional information: No such interface supported CAUSE The event wrapper classes in the interop assembly that is generated for Excel have access privileges that are too strict. Because these wrapper classes are marked Private, the universal runtime disallows an IUnknown::QueryInterface call to the wrapper classes and returns E_NOINTERFACE. This translates to the exception error that is described in the "Symptoms" section. RESOLUTION To work around this problem, you can manually modify the interop assembly that is generated for Excel to relax the access privileges for the event wrapper classes. To do this, follow these steps: Save and close your Visual Studio .NET project. Open a Visual Studio .NET command prompt and change the directory to the output directory of your project (for example, project name\bin for a Visual Basic project or project name\bin\release for a C# project). Use Ildasm.exe to extract the intermediate language from the Excel interop assembly, as follows: ildasm.exe /source Interop.Excel.dll /output=Interop.Excel.il Open Interop.Excel.il in a text editor such as WordPad and search for occurrences of "_SinkHelper". Change the access privileges of the _SinkHelper classes from Private to Public, and then save and close Interop.Excel.il. At the Visual Studio .NET command prompt, use Ilasm.exe with the /dll switch to recompile the intermediate language file into an interop assembly, as follows: ilasm.exe /dll Interop.Excel.il /output=Interop.Excel.dll Open your project in Visual Studio .NET. Add a reference to the Interop.Excel.dll that you created in step 5. To do this, follow these steps: IMPORTANT: These steps are required. If you do not set a reference to the new interop assembly, Visual Studio .NET regenerates the interop assembly when you compile the project or create a setup package. In Visual Studio .NET Solution Explorer, right-click Excel in the list of project references, and then click Remove. On the Project menu, click Add Reference. On the .NET tab, click Browse, locate the Interop.Excel.dll file in the output directory of your project, and then click Open. Click OK in the Add References dialog box to accept your selection. Test the program again with the modified interop assembly. To do this, follow these steps: Press F5 to rebuild and to run the program. When Form1 appears, click Button1 to start Excel. Start a new workbook, and then enter data in any cell. On the View menu in Visual Studio .NET, click Other Windows and then click Output. The "Change Event Triggered" text in the Output window confirms that your program handled the event. Hope this helps, -Mike G. C# Corner Autor