private void ShowEditForm(object sender, EventArgs e)
        {
            var studentEdit = new StudentEditForm(_student.StudentId.ToString());

            studentEdit.ShowDialog();
            Close();
        }
 private void ShowStudentEditForm(object sender, EventArgs e)
 {
     if (studentsListBox.SelectedIndex == -1)
     {
         MessageBox.Show("Odaberi ucenika!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
     }
     else
     {
         var studentEdit = new StudentEditForm(studentsListBox.SelectedItem.ToString().OnlyNumbers());
         studentEdit.ShowDialog();
         FillStudentsListBox();
     }
 }