Question

I have seen many object reference not set to an instance of an object questions, but I couldn’t find my scenario in any.

I have a combo box named comboBox1. While form loads I have code to populate combobox:

  private void Form1_Load(object sender, EventArgs e)
  {
        // TODO: This line of code loads data into the
        // 'tenderDBDataSet.tbl_Tender_To_Details' table.
        // You can move, or remove it, as needed.
        OleDbCommand cmd = new OleDbCommand("SELECT DISTINCT 
            tbl_Tender_To_Details.To_Name, tbl_Tender_To_Details.To_Address1, 
            tbl_Tender_To_Details.To_Address2, 
            tbl_Tender_To_Details.To_City, tbl_Tender_To_Details.To_PinCode "+
            "FROM tbl_Tender_To_Details "+
            "WHERE to_Name IS NOT NULL ", conn);
        try
        {
            conn.Open();
            OleDbDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                comboBox1.Items.Add(reader["To_Name"]);
                // listBox1.Items.Add(reader[0].ToString());
                // MessageBox.Show(reader[0].ToString());
            }
            reader.Close();
            comboBox1.SelectedIndex = 0;
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            conn.Close();
        }
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        MessageBox.Show(comboBox1.SelectedValue.ToString());
    }

The MessageBox.Show(comboBox1.SelectedValue.ToString()); line shows:

“Object reference not set to an instance of an object for combo box”.

But my surprise is the value at index 0 is set to combo box while form loads after this object reference msg box.

Answer 1

you can try put this statement at page load and make sure the combobox has loaded with items or not??

comboBox1.SelectedIndex = 0; 

if you are using winforms then try put that statement in initializecomponent() function

comboBox1.SelectedIndex = 0;