Displaying data from SQL DB table into Textbox

AutoPostBack="True" OnSelectedIndexChanged="droplist1_SelectedIndexChanged"

protected void droplist1_SelectedIndexChanged(object sender, EventArgs e)
   {
       using (SqlConnection con = new SqlConnection(conn))
       {
           string query = "select * from Login where uname='" + droplist1.SelectedValue + "' ";
           SqlDataAdapter da = new SqlDataAdapter(query, con);
           DataSet ds = new DataSet();
           da.Fill(ds);
           if (ds.Tables[0].Rows.Count > 0)
           {
               txtbox1.Text=ds.Tables[0].Rows[0].ItemArray[0].ToString();
           }
       }

   }

dim str as string 
str="select column from tablename where colname=@condition"
dim con as new SqlConnection("Data Source=.;Initial Catalog=master; uid=sa;pwd=12335")
dim cmd as new SqlCommand(str,con)
cmd.CommandType=CommandType.Text
cmd.Paramaters.AddWithValue("@condition",DropDownList1.SelectedValue)
dim adap as new SqlDataAdapter(cmd)

dim dt as new DataTable
adap.fill(dt)
TextBox1.text=dt.Rows(0)(0).ToString()