adding items to list string but getting null reference exception

Question

I am adding items to string list and i know there is data that exists to insert but i keep getting the null reference error message Object reference not set to an instance of an object.

    public class ExcelRow
        {
            public List<String> lstCells;
            public byte[] rowHash;
            ......
        }
    public class ExcelInfo
        {
            public List<ExcelRow> excelRows;
        }

    public ExcelInfo ReadExcel(OpenFileDialog openFileDialog)
        {
            var _excelFile = new ExcelQueryFactory(openFileDialog.FileName);
            var _info = from c in _excelFile.WorksheetNoHeader() select c;

            ExcelRow excelRow;
            ExcelInfo resp;

            resp = new ExcelInfo();

            foreach (var item in _info)
            {
                excelRow = new ExcelRow();
                excelRow.lstCells.Add(item.ElementAt(0));
                excelRow.lstCells.Add(item.ElementAt(1));
                excelRow.lstCells.Add(item.ElementAt(2));
                excelRow.lstCells.Add(item.ElementAt(3));
                .....
                excelRow.CalculateHash();
                resp.excelRows.Add(excelRow);
             }
            return resp;
       }

This is where i am getting the error: excelRow.lstCells.Add(item.ElementAt(0));

Almost all cases of `NullReferenceException` are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Aug 27 '13 at 02:03

King King · Accepted Answer · 2013-08-27T01:57:30.347

2

You need to initialize your lstCells in your ExcelRow constructor:

public class ExcelRow {
  public List<String> lstCells;
  public byte[] rowHash;
  public ExcelRow(){
     lstCells = new List<string>();
  }
  //....
}

public class ExcelInfo {
  public List<ExcelRow> excelRows = new List<ExcelRow>();
}

edited Aug 27 '13 at 01:57

answered Aug 27 '13 at 01:48

King King

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Thanks that worked for adding all my items but now i am getting the same thing when i hit `resp.excelRows.Add(excelRow);` and i could see that excelRow does contain items – Masriyah Aug 27 '13 at 01:54
While at it, `ExcelInfo.excelRows` is never initialized either from the code shown. – Timothy Walters Aug 27 '13 at 01:56
@Masriyah yes, you have also to initialize the `excelRows`. – King King Aug 27 '13 at 01:58

score 1 · Answer 2 · answered Aug 27 '13 at 01:49

You are not showing your ExcelRow constructor, but from the error, I am guessing you never instantiate lstCells and it remains null.

You could find this out by debugging your program and mousing over each item in the line or methodically removing one item at a time from the line until it starts working again. and deducing the problem.

adding items to list string but getting null reference exception

2 Answers2