Selected Values in a combobox is not reading

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C#

.NET

cmd = new SqlCommand("select intrfacname from transfer where ipad='" + comboBox2.SelectedItem.ToString() + "'", cn.con);
dr1 = cmd.ExecuteReader();
while (dr1.Read())
{
    textBox2.Text = dr1[0].ToString();
}
dr1.Dispose();
cmd.Dispose();

Am Selecting the combo box value and read into an text box but value of that selected index is not reading in a string Before dis code i bind the values in combo box the code for that is here but it works

 private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
  cmd = new SqlCommand("select ipad from transfer where ntwrk='" + comboBox1.SelectedItem.ToString() + "'", cn.con);
            

            dr = cmd.ExecuteReader();
            DataTable dt = new DataTable();

            dt.Columns.Add("ipad", typeof(string));
           // dt.Columns.Add("contactname", typeof(string));
            dt.Load(dr);

            comboBox2.ValueMember = "ipad";
            comboBox2.DisplayMember = "ipad";
            comboBox2.DataSource = dt;
            cmd.Dispose();
            dr.Dispose();
}

But the above code for reading a value does not work help me pls