private void button3_Click(object sender, EventArgs e) { if (lbSubjects.SelectedItem != null) { QuestionAddForm form = new QuestionAddForm(((Subject)lbSubjects.SelectedItem).ID); form.ShowDialog(); int selected = ((Subject)lbSubjects.SelectedItem).ID; dgvQuestions.DataSource = null; dgvQuestions.DataSource = controller.GetQuestions(selected); } }