c# - combobox selected value wont filter any more after clearing items -

i use combobox filter datagridview data loaded database. when form loads, datagridview , combobox filled data. combobox doesn't have selected values, when choose item dropdown, datagridview filters data fine. but, when want start on pressing button refresh, load data again in datagridview, filtered data shown.

how data shown in datagridview before touching combobox?

code far...

private void form1_load(object sender, eventargs e) { this.combobox1.selectedindexchanged +=new system.eventhandler(combobox1_selectedindexchanged); } private void combobox1_selectedindexchanged(object sender, eventargs e) { dv = dt.defaultview; dv.rowfilter=string.format("status '%{0}'", combobox1.selecteditem.tostring()); datagridview1.datasource = dv; } private void button1refresh_click(object sender, eventargs e) { combobox1.datasource = null; //doesn't work combobox1.text = ""; //clears first item in combobox, still filters combobox1.items.clear(); //clears items still filters combobox1.selectedindex = -1; //sets combobox -1, filters combobox1.resettext(); //doesnt work dt.clear(); datagridview1.datasource = null; datagridview1.rows.clear(); datagridview1.refresh(); fillldata(); //invoke function fill datagridview again , combobox //this function works great @ first run, after clicking on refresh, show's filtered data  } 

thank in advance