Cannot perform runtime binding on a null reference on C# String.IsNullorEmpty in VS2019

Question

I use the String.IsNullorEmpty to check if a cell in Excel worksheet is null or empty. Why VS2019 still reports a error if the cell is empty? I am sure the worksheet wshIO exists and the intRowIO is 1 when this error came out. The code associated with this worksheet before this line works very well.

Note, don't paste images of code or errors. They re hard to read, and cannot be searched by a search engines and indexed. Instead paste that actual code, and the actual exception — TheGeneral
– TheGeneral, Commented Dec 16, 2020 at 2:33

halfer · Accepted Answer · 2020-12-17 19:07:25Z

4

You are calling ToString on (potentially) a null dynamic type.

For instance, it's the same scenario as the following:

dynamic s = null;
s.ToString(); // Cannot perform runtime binding on a null reference

One fix is to use the null conditional operator, which will check the dynamic type for null.

string.IsNullOrEmpty(s?.ToString());

Or related to your example:

string.IsNullOrEmpty(something.Cells[x,y].Value2?.ToString())

edited Dec 17, 2020 at 19:07

halfer

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answered Dec 16, 2020 at 2:31

TheGeneral

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2 Comments

Peter Lau Over a year ago

Thank you, General. You are right. Actually I just need to check if the range is null. I don't need to get the string from the range, which might be Null. I used something.Cells[x,y]!=Null solved the issue.

Peter Lau Over a year ago

Eventually, I use string.IsNullOrEmpty(something.Cells[x,y].Text) in my code as Cells[x,y]!=Null does not work actually. !=Null cannot detect a blank cell. I don't know why. I guess that's a separated question.

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