c# - SelectedValue for ComboBox not getting set -

i have combobox name cmbcontacttype. binded combo datasource displaymember valuename(string type) , valuemember valueid(number type). when user change value in cmbcontacttype cmbcontacttype.selectvalue set , able save document selectedvalue. facing problem while setting cmbcontacttype value database of type number. every time trying set value, null value set cmbcontacttype.selectvalue. following code binding datasource cmbcontacttype , setting selectedvalue of cmbcontacttype. using vs2010 , ms-access. please help.

    //method bind datasource.     public static void binddatasourcewithcombo(ref combobox cmb, string query, string valuemember, string displaymember)     {         datatable _tablesource = (new accessconnectionmanager()).getdatatablebysqlquery(query);          var _datasource = (from datarow _row in _tablesource.rows                            select new                            {                                valuemember = _row[valuemember],                                displaymember = _row[displaymember].tostring()                             }).tolist();          cmb.displaymember = "displaymember";         cmb.valuemember = "valuemember";         cmb.datasource = _datasource;     }      // method set values in document.     public void setdocumentproperties()     {         string _query = string.format("select contactcode,contactname,contacttype contactmaster contactcode = '{0}'", convert.tostring(cmbcontactcode.text));         datatable _table = accessconnectionmanagers.getdatatablebysqlquery(_query);          if (_table.rows.count > 0)         {             datarow _row = _table.rows[0];             txtcontactcode.text = convert.tostring(_row["contactcode"]);             txtcontactname.text = convert.tostring(_row["contactname"]);             cmbcontacttype.selectedvalue = _row["contacttype"];         }         else         {             txtcontactcode.text = string.empty;             txtcontactname.text = string.empty;             cmbcontacttype.selectedvalue = 1;         }     } 

here code bind datasource cmbconacttype. method call on form_load event.

    private void loadcontacttypecombo()     {         //table: picklistvalues(id,masterid,valueid,valuename)          string _query = string.format("select valueid,valuename picklistvalues masterid = {0}", 1);         binddatasourcewithcombo(ref cmbcontacttype, _query, "valueid", "valuename");     } 

try method

int index; // search item matches string index=cmbcontacttype.findstring(_row["contacttype"]); // select item in combo cmbcontacttype.selectedindex=index;