private void btnLoginRegister_Click(object sender, EventArgs e) { if (!String.IsNullOrEmpty(this.txbLoginEmail.Text) && !String.IsNullOrEmpty(this.txbLoginPassword.Text)) { bool IsExists = false; foreach (var user in DatabaseSecond.Users.GetAll()) { if (user.Email == this.txbLoginEmail.Text && user.Password == this.txbLoginPassword.Text) { MessageBox.Show("Successfully Logined!"); BookControl bookControl = new BookControl(this); bookControl.ShowDialog(); IsExists = true; break; } } if (!IsExists) { MessageBox.Show("Email or password is wrong! Please try again!"); } } else { MessageBox.Show("All fields must be filled!"); } }