ComboBox, three-level linkage menu, new entry point small white, some code needs to be optimized, big God do not spray

//Load event for the current form        Private voidProvinceandcity_load (Objectsender, EventArgs e) {            //Connection String            stringstrconn ="Data Source=.;i Nitial catalog=province; User Id=sa; Pwd=ok"; //Connection ObjectSqlConnection conn =NewSqlConnection (strconn); //DataSet ObjectDataSet ds =NewDataSet (); //Query Province Statement            stringsql ="SELECT * from province"; SqlDataAdapter Adapter=NewSqlDataAdapter (Sql,conn); Adapter. Fill (DS,"Province"); //bind the province's data to a drop-down box in the province             This. Cboprovince.datasource = ds. tables["Province"];  This. Cboprovince.valuemember ="ID";  This. Cboprovince.displaymember ="Provincename"; //get the province number            intid = Convert.ToInt32 ( This. Cboprovince.selectedvalue); //Search Cities by province numbersql ="SELECT * from city WHERE proid="+ID; Adapter=NewSqlDataAdapter (Sql,conn); Adapter. Fill (DS," City"); //will find out the city bound in the City drop-down box             This. Cbocity.datasource = ds. tables[" City"];  This. Cbocity.valuemember ="ID";  This. Cbocity.displaymember ="CityName"; //Get City Number            intCityid = Convert.ToInt32 ( This. Cbocity.selectedvalue); //Search Districts by city numbersql ="SELECT * from county WHERE cityid="+Cityid; Adapter=NewSqlDataAdapter (SQL, conn); Adapter. Fill (DS,"County"); //The counties to be found are bound in the county drop-down box             This. Cbocounty.datasource = ds. tables["County"];  This. Cbocounty.valuemember ="ID";  This. Cbocounty.displaymember ="Countyname"; }        //events in the province drop-down box        Private voidCboprovince_selectionchangecommitted (Objectsender, EventArgs e) {            stringstrconn ="Data Source=.;i Nitial catalog=province; User Id=sa; Pwd=ok"; SqlConnection Conn=NewSqlConnection (strconn); DataSet DS=NewDataSet (); //get the province number            intid = Convert.ToInt32 ( This. Cboprovince.selectedvalue); //Search Cities by province number            stringsql ="SELECT * from city WHERE proid="+ID; SqlDataAdapter Adapter=NewSqlDataAdapter (SQL, conn); Adapter. Fill (DS," City"); //will find out the city bound in the City drop-down box             This. Cbocity.datasource = ds. tables[" City"];  This. Cbocity.valuemember ="ID";  This. Cbocity.displaymember ="CityName"; }        //City drop-down box events        Private voidCbocity_selectionchangecommitted (Objectsender, EventArgs e) {            stringstrconn ="Data Source=.;i Nitial catalog=province; User Id=sa; Pwd=ok"; SqlConnection Conn=NewSqlConnection (strconn); DataSet DS=NewDataSet (); //Get City Number            intCityid = Convert.ToInt32 ( This. Cbocity.selectedvalue); //Search Districts by city number            stringsql ="SELECT * from county WHERE cityid="+Cityid; SqlDataAdapter Adapter=NewSqlDataAdapter (SQL, conn); Adapter. Fill (DS,"County"); //The counties to be found are bound in the county drop-down box             This. Cbocounty.datasource = ds. tables["County"];  This. Cbocounty.valuemember ="ID";  This. Cbocounty.displaymember ="Countyname"; }

ComboBox, three-level linkage menu, new entry point small white, some code needs to be optimized, big God do not spray