private void btn_Edit_Activities_Click(object sender, EventArgs e)
{
var selectedItem = listViewActivities.SelectedItems[0];
Activity selectedActivity = activities.Where(t => t.countStudents == int.Parse(selectedItem.Text)).FirstOrDefault();
ActivityDialog activityDialog = new ActivityDialog(selectedActivity);
activityDialog.Show();
btn_Edit_Activities.Enabled = false;
btn_Add_Activity.Enabled = false;
}
private void btn_Add_Activity_Click(object sender, EventArgs e)
{
ActivityDialog activityDialog = new ActivityDialog();
activityDialog.Show();
}