private void btRegistreer_Click(object sender, EventArgs e)
        {
            try
            {
                SQLService sqlService = new SQLService();
                sqlService.Insert("INSERT INTO gebruiker (username,password,user_voornaam,user_achternaam,email,admin_level) VALUES ('Josh', 'Josh','Josh','Josh','Josh',1) ");
            }
            catch (Exception obj)
            {

                MessageBox.Show(obj.Message);
            }
        }
        private void btLogin_Click(object sender, EventArgs e)
        {
            try
            {
                SQLService sqlService = new SQLService();
                bool bestaat = sqlService.Bestaat("SELECT * FROM gebruiker WHERE username = '******' AND password = '******' ");

                if (bestaat == false)
                {
                    MessageBox.Show("Bestaat niet");
                }
                else
                {
                    MessageBox.Show("Bestaat");
                }
            }
            catch (Exception)
            {

                throw;
            }
        }
 private void bt_Add_Click(object sender, EventArgs e)
 {
     SQLService sqlService = new SQLService();
     sqlService.Insert("INSERT INTO Categorie (Catergorie_naam) VALUES('" + textBox1.Text +"')");
 }