Exception (nullreferenceexception) on datagridview

Question

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Is anybody can help me understand the issue of my code? It is always going to the exception, does not matter if I try to "treat" the cell with NULL.

My catch System.Exception error is:
"Object reference not set to an instance of an object"

C#

try
 {

     worksheet = workbook.ActiveSheet;

     worksheet.Name = "ExportedFromDatGrid";

     int cellRowIndex = 1;
     int cellColumnIndex = 1;


     //Loop through each row and read value from each column.
     for (int i = -1; i < dataGridView1.Rows.Count - 1; i++)
     {
         for (int j = 0; j < dataGridView1.Columns.Count; j++)
         {
             // Excel index starts from 1,1. As first Row would have the Column headers, adding a condition check.
             if (cellRowIndex == 1)
             {
                 worksheet.Cells[cellRowIndex, cellColumnIndex] = dataGridView1.Columns[j].HeaderText;
             }
             else
             {

                 if (dataGridView1.Rows[i].Cells[j].Value.ToString() != null)
                 {
                     worksheet.Cells[cellRowIndex, cellColumnIndex] = dataGridView1.Rows[i].Cells[j].Value.ToString();
                 }
                 else
                 {
                     worksheet.Cells[cellRowIndex, cellColumnIndex] = String.Empty;
                 }


                 // working:
                 //worksheet.Cells[cellRowIndex, cellColumnIndex] = dataGridView1.Rows[i].Cells[j].Value.ToString();
             }
             cellColumnIndex++;
         }
         cellColumnIndex = 1;
         cellRowIndex++;
     }

     //Getting the location and file name of the excel to save from user.
     SaveFileDialog saveDialog = new SaveFileDialog();
     saveDialog.Filter = "Excel files (*.xlsx)|*.xlsx|All files (*.*)|*.*";
     saveDialog.FilterIndex = 2;

     if (saveDialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
     {
         workbook.SaveAs(saveDialog.FileName);
         MessageBox.Show("Export Successful");
     }
 }
 catch (System.Exception ex)
 {
     MessageBox.Show(ex.Message);
 }
 finally
 {
     excel.Quit();
     workbook = null;
     excel = null;
 }

What I have tried:

I tried, with no success, to use an IF/ELSE condition to avoid the program entering the "exception".

Posted 8-Jun-17 7:38am

Member 13248805

Updated 19-Oct-20 21:56pm

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Comments

ZurdoDev 8-Jun-17 14:16pm

This is very, very simple. But no one can help unless you tell us which line of code is causing the error.

2 solutions

Solution 2

if (dataGridView1.Rows[i].Cells[j].Value.ToString() != null)

the above throws exception if null found. use below step instead of above.

if ( (dataGridView1.Rows[i].Cells[j].Value ?? "").ToString() != "")

Posted 19-Oct-20 21:57pm

Santhosh Ks

Updated 19-Oct-20 21:58pm

v2

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Richard Deeming · Accepted Answer · 2017-06-08T08:25:00

Your catch block isn't helping you - you're throwing away almost all of the useful details of the exception, and preventing Visual Studio from breaking when the exception is thrown.

But at a guess, the exception is probably thrown from this line:

if (dataGridView1.Rows[i].Cells[j].Value.ToString() != null)

If the Value is null, you'll get a NullReferenceException when you try to call ToString on it.

If the Value is not null, then ToString will not return null.

Remove the .ToString() call on that line.

if (dataGridView1.Rows[i].Cells[j].Value != null)
{
    worksheet.Cells[cellRowIndex, cellColumnIndex] = dataGridView1.Rows[i].Cells[j].Value.ToString();
}
else
{
    worksheet.Cells[cellRowIndex, cellColumnIndex] = String.Empty;
}