NullReferenceException when searching for data in DataGridView

Question

Hi I've written this code to search for cardserial in a gridview. But I get an error :

"Object reference not set to an instance of an object."

foreach (DataGridViewRow row in dataGridView2.Rows)
{
    if (row.Cells["CardSerial"].Value.ToString().Equals(textBox2.Text))
    {
        dataGridView2.Rows[row.Index].DefaultCellStyle.BackColor = Color.Yellow;
    }
}

Could you tell me what's the problem?

Answer 1

First check if value in the cell is not null (if it is calling ToString on it fails)

foreach (DataGridViewRow row in dataGridView2.Rows)
{
    var serial = row.Cells["CardSerial"].Value;

    if (serial != null && serial.ToString().Equals(textBox2.Text))
    {
        row.DefaultCellStyle.BackColor = Color.Yellow;
    }
}

Answer 2

Most likely, of the following is null, which is causing the exception when you dereference it:

• dataGridView2
• row.Cells["CardSerial"]
• row.Cells["CardSerial"].Value
• textBox2
• dataGridView2.Rows[row.Index]
• dataGridView2.Rows[row.Index].DefaultCellStyle

To find out which one, debug your program, and make use of the watch window, immediate window, or add a number of debug/trace output lines.

Of specific note may be the case where row.Cells["CardSerial"].Value is null.