Set DroDownList selected value in GridView Row using C# in ASP.Net

The DropDownList is not retrieving values from database.

I want to set selected value of DropDownList in GridView row.

Can u please help me?

        protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                DropDownList txtdepname = (e.Row.FindControl("txtdepname") as DropDownList);

                string str = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\sivaranjani\\Documents\\Database6.accdb";
                OleDbConnection db = new OleDbConnection(str);
                db.Open();
                string st = "select DEPNAME,DID from tab";
                OleDbCommand dbc = new OleDbCommand(st, db);
                OleDbDataReader read = dbc.ExecuteReader();

                txtdepname.DataSource = read;
                txtdepname.DataTextField = "DEPNAME";
                txtdepname.DataValueField = "DID";
                txtdepname.DataBind();
                read.Close();
                db.Close();
            }
        }

       protected void ShowData()
       { 
           OleDbConnection connn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\sivaranjani\Documents\Database6.accdb");
           connn.Open();
           OleDbCommand cmd = new OleDbCommand("Select [emp].[ID],[emp].[EMPID],[emp].[EMPNAME],[emp].[AGE],[tab].[DEPNAME] from emp INNER JOIN tab ON [emp].[DID] = [tab].[DID]  ", connn);
           OleDbDataReader rd = cmd.ExecuteReader();
           DataTable dt = new DataTable();
           dt.Load(rd);
           connn.Close();
           if (dt.Rows.Count > 0)
           {
               GridView1.DataSource = dt;
               GridView1.DataBind();
           }
           else
           {
               dt.Rows.Add(dt.NewRow());
               GridView1.DataSource = dt;
               GridView1.DataBind();
               int columncount = GridView1.Rows[0].Cells.Count;
               GridView1.Rows[0].Cells.Clear();
               GridView1.Rows[0].Cells.Add(new TableCell());
               GridView1.Rows[0].Cells[0].ColumnSpan = columncount;
               GridView1.Rows[0].Cells[0].Text = "No Records Found";
           }
       }