Correct way to check for null objects?

Question

Hi all,
I'm using the Precedents object of an Excel Range:

Excel.Range range = (Excel.Range)Globals.ThisAddIn.Application.ActiveCell;
foreach (Excel.Range r in range.Precedents)
                {
                    //stuff
                }

When there are precedents, this is fine.  However if there are no precedents, I get a COMException.  I'd like to do a check to prevent the exception, but "normal" checks for null/empty objects don't work, such as:
if (range.Precedents == null)
if (range.Precedents.Count > 0)

These throw the same COMException.  It seems you can't "touch" a null/empty object at all.

Placing everything inside a try/catch works, but this feels like the wrong way to be coding, is there a better option?
Thanks...

Answer 1

Are you checking to make sure range is not null as well?

---

William Wegerson (www.OmegaCoder.Com)

Answer 2

The range is not null, even in the case of a new worksheet/blank cell.

 if (range != null)
            {
              //this executes
            }

Answer 3

Hello Jonathan,

If the range has not precedents, it will throw an exception when accessing this property. Here, it is right way to use try/catch block. Code like this:
            try
            {               
                foreach (Excel.Range r in range.Precedents)
                {
                    ......
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

If you have any further question, please feel free to let us know.

Best regards,
Bessie

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Answer 4

This is the fastest option, and you can check that the error message returned is "No cells were found."

There is a much slower way of doing this, and that is to
 - ShowPrecendents
 - NavigateArrows

cheers

Answer 5

Hi all,
Thanks for the replies.  I've implemented the try/catch(s) and they work fine.  Was hoping for something that made the code "cleaner", but if that's the way it is, that's the way it is...
-Jon