Preventing users from using an instance of Excel

I'm using Microsoft.Office.Interop.Excel to create Excel reports with C#. Those reports have a large amount of graphics and take long time to prepare. During the preparation, The instance of the Excel application that my program uses is hidden from the user.

MY problem is that Microsoft Office tends to share application instances automatically. If the user opens an Excel workbook, Excel will try to find a running instance of Excel and open the document from there. When the user tries to open an Excel workbook while my program is running, it is attached to the instance my program uses.

This generates two problem. First, it forces my reports into visibility before they are supposed to become visible. And second, my program now needs to fight with user over the attention of the Excel instance - and my program usually loses.

So, is there any way to make the Excel instance reject requests(from the user. it should still obey to my program) to open documents, and make Office ignore my instance when it has to decide how to open an Excel document?

You could handle the Application.WorkbookOpen event. In here, either start a second instance of Excel and have it open the workbook, or close the workbook with an error message.

I also saw the Application.Interactive property. I haven't played with this, but it may be of use to you.

You can use NPOI, I suggest you visit the following link

http://npoi.codeplex.com/discussions/36157?ProjectName=npoi

I have done a little experimenting, and I think this will work:

Whenever you begin working with Excel, create two instances, and work with the second. When you're done with your work, delete the second instance and its object, then check the "UserControl" property of the first. If it returns "true", then delete only the object, but leave the process for that instance behind. If it returns "false", then delete the instance as well.

As far as I can tell, the user can open and close any number of workbooks, and it will use the first instance you created, as long as you don't delete it, and the second instance will be unmolested.