private void Btn_AddAct_Click(object sender, EventArgs e)
        {
            List <Activity> activities = activityService.GetActivities();

            if (txt_ActDate.Text == "" || txt_ActID.Text == "" || txt_description.Text == "" || txt_NumGuides.Text == "" || txt_NumPart.Text == "")
            {
                MessageBox.Show("Please fill in ALL the fields to succesfully add an activity");
                return;
            }

            foreach (Activity act in activities)
            {
                if (txt_description.Text.ToLower() == act.Description.ToLower() || txt_ActID.Text == act.ActivityID.ToString())
                {
                    MessageBox.Show("The description or ID of an activity can not be the same as another activity");

                    txt_ActDate.Clear();
                    txt_ActID.Clear();
                    txt_description.Clear();
                    txt_NumGuides.Clear();
                    txt_NumPart.Clear();

                    return;
                }
            }

            string query = "INSERT INTO activities VALUES (" + txt_ActID.Text + ", '" + @txt_description.Text + "', " + @txt_NumGuides.Text + ", " + @txt_NumPart.Text + ", '" + @txt_ActDate.Text + "')";

            activityService.UpdateActivity(query);

            this.Close();
        }
        private void Btn_EditAct_Click(object sender, EventArgs e)
        {
            string   newDescription;
            Int16    newNumGuides;
            Int16    newNumPart;
            DateTime newDate;

            List <Activity> activities = activityService.GetActivities();


            if (txt_description.Text == "")
            {
                newDescription = selectedAct.Description;
            }
            else
            {
                foreach (Activity act in activities)
                {
                    if (txt_description.Text == act.Description)
                    {
                        MessageBox.Show("There already is an activity like this, please choose something else");
                        txt_description.Clear();
                        txt_ActDate.Clear();
                        txt_NumGuides.Clear();
                        txt_NumPart.Clear();

                        return;
                    }
                }

                newDescription = txt_description.Text;
            }

            if (txt_NumGuides.Text == "")
            {
                newNumGuides = selectedAct.NumberOfGuides;
            }
            else
            {
                newNumGuides = Int16.Parse(txt_NumGuides.Text);
            }

            if (txt_NumPart.Text == "")
            {
                newNumPart = selectedAct.NumberOfParticipants;
            }
            else
            {
                newNumPart = Int16.Parse(txt_NumPart.Text);
            }

            if (txt_ActDate.Text == "")
            {
                newDate = selectedAct.ActivityDate;
            }
            else
            {
                newDate = DateTime.Parse(txt_ActDate.Text);
            }

            string query = "UPDATE activities SET [description]='" + newDescription + "', numberOfGuides=" + newNumGuides + ", numberOfParticipants=" + newNumPart + ", [date]='" + newDate.ToString("yyyy/MM/dd") + "' WHERE activityID=" + selectedAct.ActivityID;

            activityService.UpdateActivity(query);

            this.Close();
        }