Hi Scott,
Thank you for your interest in Essential XlsIO.
We do not have any API to check if a worksheet object has been closed or not. But you can you can check this by using below code snippet.
[C#]
try
{
workbook.Close();
}
catch (System.NullReferenceException ex)
{
MessageBox.Show("workbook is already closed");
}
Please refer the sample in the below link which illustrates the above.
http://websamples.syncfusion.com/samples/XlsIO.Windows/66721/main.htmPlease try this and let me know if this helps.
Thanks,
Melba