title: "Object reference not set to an instance of an object" in my gridview
body: <p>what can i do... i tried many codes by searching google but failed... plz help me</p>
  
  <pre><code>protected void RegistrationDetails_RowUpdating(object sender, GridViewUpdateEventArgs e)
      {
          int stdid = Convert.ToInt32(RegistrationDetails.DataKeys[e.RowIndex].Value.ToString());
          int stdroll = Convert.ToInt32(RegistrationDetails.DataKeys[e.RowIndex].Value.ToString());
          int clsid = Convert.ToInt32(RegistrationDetails.DataKeys[e.RowIndex].Value.ToString());
          //DateTime tdob = Convert.ToDateTime(RegistrationDetails.DataKeys[e.RowIndex].Value);
          int vyear = Convert.ToInt32(RegistrationDetails.DataKeys[e.RowIndex].Value.ToString());
          //DateTime vadmdate = Convert.ToDateTime(RegistrationDetails.DataKeys[e.RowIndex].Value);
          GridViewRow row = (GridViewRow)RegistrationDetails.Rows[e.RowIndex]; 
          Label lblID = (Label)RegistrationDetails.Rows[e.RowIndex].FindControl("lblID");
          //TextBox txtname=(TextBox)gr.cell[].control[];  
          //TextBox tid = RegistrationDetails.Rows[e.RowIndex].Cells[0].Controls[0] as TextBox;
          //TextBox troll = RegistrationDetails.Rows[e.RowIndex].Cells[1].Controls[0] as TextBox;
          TextBox tname = RegistrationDetails.Rows[e.RowIndex].Cells[3].Controls[0] as TextBox;
          TextBox tdob = RegistrationDetails.Rows[e.RowIndex].Cells[4].Controls[0] as TextBox;
          TextBox taddress = RegistrationDetails.Rows[e.RowIndex].Cells[5].Controls[0] as TextBox;
          TextBox tcontactp = RegistrationDetails.Rows[e.RowIndex].Cells[6].Controls[0] as TextBox;
          TextBox tgender = RegistrationDetails.Rows[e.RowIndex].Cells[7].Controls[0] as TextBox;
          TextBox tmobile = RegistrationDetails.Rows[e.RowIndex].Cells[8].Controls[0] as TextBox;
          //TextBox tyear = RegistrationDetails.Rows[e.RowIndex].Cells[8].Controls[0] as TextBox;
          TextBox tjdate = RegistrationDetails.Rows[e.RowIndex].Cells[10].Controls[0] as TextBox;
          TextBox tpass = RegistrationDetails.Rows[e.RowIndex].Cells[11].Controls[0] as TextBox;
          //TextBox tclsid = RegistrationDetails.Rows[e.RowIndex].Cells[11].Controls[0] as TextBox;
          TextBox tsecid = RegistrationDetails.Rows[e.RowIndex].Cells[12].Controls[0] as TextBox;
  
          //string vfullname = fullname.Text;
          //string vaddress = address.Text;
          //string vcperson = cperson.Text;
          //string vmobile = mobile.Text;
          //string vpass = pass.Text;
          //TextBox textadd = (TextBox)row.FindControl("txtadd");  
          //TextBox textc = (TextBox)row.FindControl("txtc");  
          RegistrationDetails.EditIndex = -1;
          con.Open();
          //SqlCommand cmd = new SqlCommand("SELECT * FROM detail", conn);  
          OleDbCommand cmd = new OleDbCommand("update registration set Roll=" + stdroll + ", Full_Name='" + tname.Text + "', Date_of_Birth='" + tdob.Text + "',Address='" + taddress.Text.Trim() + "', Contact_Person='" + tcontactp.Text + "', Gender='" + tgender.Text + "', Mobile='" + tmobile.Text + "', CYear=" + vyear + ", Joining_Date='" + tjdate.Text + "', UPassword='" + tpass.Text + "', Class_ID=" + clsid + ", Section_ID='" + tsecid.Text + "' where Student_ID=" + stdid + "", con);
          cmd.ExecuteNonQuery();
          con.Close();
          refreshdata();
      }
  </code></pre>