Our application exports snippets of databases in XLSX format. We wrote our own code on top of System.Packaging as it is many (many!) times faster than using the Excel objects.
Right now we save these files with a .xlsx format, and that works OK. However, it would be much nicer if double-clicking one of these opened our app instead, but failed back to Excel on machines without it.
I know that SpreadsheetML has a feature to do this. If you insert this near the top of the file:
<?mso-application progid=""Excel.Sheet""?>
some sort of magic occurs that causes Excel to open on Win machines. While this might work in SML files, it does not appear to work in "real" xlsx files - I tried adding this line to various parts of the workbook structure but it remained unrecognized.
So is there a similar mechanism we can use in "true" XLSX files generated by System.Packaging? Or some other Windows mechanism we should use in these situations?