Drop down list in Asp.net using C#

Click on drop down list in write this code

{

    string str = "server = MUNESH\\SQL2008R2;Database=datastore;UID=sa;Password=123;";

    SqlConnection con = new SqlConnection(str);

    string query = "select * from tablename where name = '"+dropdownlist.text+"' ";

    SqlCommand cmd = new SqlCommand( query,con);

    sqldatareader dbr;

    try

    {

        con.open();

        dbr = cmd.executereader();

        while(dbr.read())

        {

            string sID = (string) dbr["ID"].tostring;

            string sname = (string) dbr["name"] // name is string value

            string sage = (string) dbr["age"].tostring;

            textbox1.text = sid;

            textbox2.text = sname;

            textbox3.text = sage;

            showgrid();

        }

        catch(execption es)

        {

           messagebox.show(es.message);

        }

    }