template filed text box does not show value

i have use textbox cells[12] but doesn't display value when click on imahe button on gried view

if (e.CommandName == "select")
{

for (int i = 0; i < gv_rap.Rows.Count; i++)
{
var color = ((Label)gv_rap.Rows[i].Cells[3].FindControl("lblcolor")).Text.Trim(); //If its label
var cl = ((Label)gv_rap.Rows[i].Cells[4].FindControl("lblclearity")).Text.Trim();
var shape = ((Label)gv_rap.Rows[i].Cells[7].FindControl("lblshape")).Text.Trim();
string frm = ((DropDownList)gv_rap.Rows[i].Cells[12].FindControl("ddlfrm")).Text.Trim();
string to = ((DropDownList)gv_rap.Rows[i].Cells[13].FindControl("ddlto")).Text.Trim();

TextBox txtrap = ((TextBox)gv_rap.Rows[i].Cells[14].FindControl("txtrap"));
string str = "select rap from test where frm='" + frm+ "'and tom='" + to + "'and round='" + shape + "'and clearity='" + cl + "'and color= '" + color + "'";
SqlCommand cmd = new SqlCommand(str, conn);
conn.Open();
SqlDataReader reader = cmd.ExecuteReader();

if (reader.Read())
{

txtrap.Text= reader["rap"].ToString();

reader.Close();

conn.Close();
}

}

above my code when click onsingle time select image button at that time all row in griedview
change value in txtrap field griedview textbox...

i have to one by one get value in txtrap taxtbox...

please help..