c# - how to fix this 'DropDownList1' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value -

public partial class allfiles : system.web.ui.page {  received re = new received(); catgories cat = new catgories(); protected void page_load(object sender, eventargs e) {     if(!ispostback)     {        dropdownlist1.datasource = cat.get_all_cat();       dropdownlist1.datatextfield = "اسم المستند";       dropdownlist1.datavaluefield = "رقم المستند";       dropdownlist1.databind();     } } protected void gridview1_selectedindexchanged1(object sender, eventargs e) {     // dropdownlist1.items.clear();    // dropdownlist1.selectedindex = 0;     textbox10.text = gridview1.selectedrow.cells[2].text;     textbox1.text = gridview1.selectedrow.cells[8].text;     textbox2.text = gridview1.selectedrow.cells[9].text;     textbox3.text = gridview1.selectedrow.cells[10].text;     textbox11.text = gridview1.selectedrow.cells[11].text;     textbox4.text = gridview1.selectedrow.cells[12].text;     textbox5.text = gridview1.selectedrow.cells[6].text;     textbox6.text = gridview1.selectedrow.cells[7].text;       dropdownlist1.selectedvalue = gridview1.selectedrow.cells[3].text;        textbox8.text = gridview1.selectedrow.cells[4].text;     textbox9.text = gridview1.selectedrow.cells[5].text;  } 

when row selected error displayed:

'dropdownlist1' has selectedvalue invalid because not exist in list of items. parameter name: value

finely found solution code

    dropdownlist1.selectedindex = dropdownlist1.items.indexof(dropdownlist1.items.findbytext(gridview1.selectedrow.cells[3].text)); 

it works