private void button1_Click(object sender, EventArgs e) { subjectObject.Notify(); string PersonCode = textBox1.Text; string Password = textBox2.Text; IPerson personOnline = businessManager.Authentication(PersonCode, Password); textBox2.Text = string.Empty; if (personOnline is Alumnus) { textBox1.Text = string.Empty; new Form3().ShowDialog(); } else if (personOnline is Employee) { textBox1.Text = string.Empty; new Form4().ShowDialog(); } else { MessageBox.Show("Invalid UserName or Password"); } businessManager = new BusinessManager(); }