private async void comboboxTeacherName_SelectedIndexChanged(object sender, EventArgs e) { try { TeacherName = comboBoxTeacherName.Items[comboBoxTeacherName.SelectedIndex].ToString(); } catch { } await Task.Factory.StartNew(() => { InvokeUI(() => { var listDiscipline = WorkWithDB.GetAllDisciplineForTeacher(TeacherName).ToList(); if (listDiscipline != null) { AddItemToComboBox(comboBoxListDiscipline, listDiscipline); } listDiscipline.Clear(); }); }); }