Object reference not set to an instance of an object - When reading dataGridView

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Hi all,

I am having a problem when trying to read cells in a DataGridView.

When the program executes the code below...

C#

for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
    if (dataGridView1.Rows[i].Cells[0].Value.ToString().Length == 0 && dataGridView1.Rows[i].Cells[1].ToString().Length != 0)
    {
        MessageBox.Show("You must enter a description for each value.");
        return;
    }
    if (dataGridView1.Rows[i].Cells[1].Value.ToString().Length == 0 && dataGridView1.Rows[i].Cells[0].ToString().Length != 0)
    {
        MessageBox.Show("You must enter a value for each description.");
        return;
    }
}

The following error appears:

Object reference not set to an instance of an object.

What I do is execute the program and type 'test' (for example), in the first field [Description]. When i Click on the button which activates the verification, the error happens.

Can someone help me? :confused:

I am using Visual Studio Team System - C#

Thanks in advance! :)

Posted 31-Oct-10 22:48pm

lucasgrohl

Updated 1-Nov-10 2:27am

Henry Minute

v5

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Hiren solanki · Answer 1 · 2010-10-31T23:06:00

Object reference not set to an instance of an object

It's a generic error which occurs when you are having any uninitialized or null valued object for which you are going to apply any operations. That's why It is considered as Exception of kind NullReferenceException.

To overcome this error always check 'Null' on the object before any operation done on it.

You could have more clarity with NullReferenceException with THIS[^] article.

Please vote and Accept Answer if it Helped.

Pawan Kiran · Answer 2 · 2010-10-31T23:04:00

Don't Refer Cells With Index, Better to Specify Column Name's.

A small change to Mr.Abhishek answer

dataGrid1.Rows[i].Cells["ColumnName"].Value != null

Replace your code with:

for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
      if (!string.IsNullOrEmpty(dataGridView1.Rows[i].Cells["Column1"].Value.ToString())&& !string.IsNullOrEmpty(dataGridView1.Rows[i].Cells["Column2"].Value.ToString())) //Above Statement is Used to Check For String is Null or Empty. By making use of string.IsnullorEmpty() We can Handle this kind of "Object Reference not set to instance of an object" situations. I am not sure how far My Code would be useful.. But have a look at this. 
       {
           if (dataGridView1.Rows[i].Cells["Column1"].Value.ToString().Length == 0
|| dataGridView1.Rows[i].Cells["Column1"].Value == null
&& dataGridView1.Rows[i].Cells[1].Value.ToString().Length != 0)
           {
                 MessageBox.Show("You must enter a description for each value.");
                 return;
           }
           if (dataGridView1.Rows[i].Cells["Column2"].Value.ToString().Length == 0 ||dataGridView1.Rows[i].Cells["Column2"].Value == null &&dataGridView1.Rows[i].Cells[0].Value.ToString().Length != 0)
           {
                 MessageBox.Show("You must enter a value for each description.");
                 return;
           }
     }
}

**JF2015** · Answer 3 · 2010-10-31T23:06:00

Hi,
try this to find your error:

C#

for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
    if (dataGridView1.Rows[i].Cells[0] == null)
    {
        MessageBox.Show("Cells[0] is null");
        continue;
    }
    if (dataGridView1.Rows[i].Cells[1] == null)
    {
        MessageBox.Show("Cells[1] is null");
        continue;
    }
    if (dataGridView1.Rows[i].Cells[0].Value.ToString().Length == 0 && dataGridView1.Rows[i].Cells[1].ToString().Length != 0)
    {
        MessageBox.Show("You must enter a description for each value.");
        return;
    }
    if (dataGridView1.Rows[i].Cells[1].Value.ToString().Length == 0 && dataGridView1.Rows[i].Cells[0].ToString().Length != 0)
    {
        MessageBox.Show("You must enter a value for each description.");
        return;
    }
}

Abhishek Sur · Answer 4 · 2010-10-31T22:54:00

Solution 1

NullReferenceException can occur in many cases.
Always it is good to check an object before calling .ToString().Length like this.
So Please ensure dataGrid1.Rows[i].Cells[1].Value != null before you call ToString().

Posted 31-Oct-10 22:54pm

Abhishek Sur

Updated 1-Nov-10 2:34am

v2

Comments

lucasgrohl 1-Nov-10 5:01am

I replaced the previous code for:

for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
if (dataGridView1.Rows[i].Cells[0].Value.ToString().Length == 0 || dataGridView1.Rows[i].Cells[0].Value == null && dataGridView1.Rows[i].Cells[1].ToString().Length != 0)
{
MessageBox.Show("You must enter a description for each value.");
return;
}

if (dataGridView1.Rows[i].Cells[1].Value.ToString().Length == 0 || dataGridView1.Rows[i].Cells[0].Value == null && dataGridView1.Rows[i].Cells[0].ToString().Length != 0)
{
MessageBox.Show("You must enter a value for each description.");
return;
}
}

But the error persists =(

fjdiewornncalwe 1-Nov-10 10:29am

if( string.IsNullOrEmpty( dataGridView1.Rows[i].Cells[0].Value ) ... You don't even have to check the length then, just do the IsNullOrEmpty check. It does both.

fjdiewornncalwe 1-Nov-10 10:30am

As a second notation. Unless you can guarantee the existence of all the objects in the hierarchy of the call, you may want to do a null check on each level of the call as well just be sure where your reference error is occuring.

Object reference not set to an instance of an object - When reading dataGridView

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