Listbox Multiselect for search function in vb.net -

i have changed dropdown listbox have multiple selection when searching not working. have included list box values , search have used in stored procedure. in advance

cmdgetdefectsymptoms.parameters("@languageid").value = strlanguage             cmdgetdefectsymptoms.parameters("@defaultlanguageid").value = configurationmanager.appsettings("defaultlanguage")             cmdgetdefectsymptoms.parameters("@failuremode").value = dbnull.value             dtrdefectsymptom = cmdgetdefectsymptoms.executereader             listbox1.datasource = dtrdefectsymptom             listbox1.databind()             dtrdefectsymptom.close()             listbox1.items.insert(0, datacom.getlocalizedlabel("ddlall", strlanguage))             listbox1.items(0).value = -1             listbox1.selectedindex = 0             listbox1.selectionmode = listselectionmode.multiple  **button search  if listbox1.items.count > 0 , listbox1.selectedindex <> 0             cmdsearchissues.parameters("@defectsymptom").value = listbox1.selecteditem.value         end if ***storedprocedure perform search  if @defectsymptom not null     begin         set @sqlwhere = @sqlwhere + n'(i.defectsymptom = @defectsymptom) and'     end