private void OnLoginButtonClickEvent(object sender, EventArgs e) { var userName = FindViewById <EditText>(Resource.Id.userName1); var password = FindViewById <EditText>(Resource.Id.password2); Regex regexUserName = new Regex(@"(?!^[0-9]*$)(?!^[a-zA-Z]*$)^([a-zA-Z0-9]{5,12})$"); Regex regexpassword = new Regex(@"^([a-zA-Z0-9@*#]{5,12})$"); Match matchUserName = regexUserName.Match(userName.Text); Match matchPassword = regexpassword.Match(password.Text); if (matchUserName.Success && matchPassword.Success) { User user = new User(); DBRepository db = new DBRepository(); user.Name = userName.Text; user.Password = password.Text; bool exists = db.CheckIfUserExist(user); if (exists) { var intent = new Intent(this, typeof(ShowListActivity)); StartActivity(intent); } else { var textmessage = FindViewById <TextView>(Resource.Id.listViewMessage); textmessage.Text = "User Name or Password is incorrect. Login with correct user name and password."; } } else { var textmessage = FindViewById <TextView>(Resource.Id.listViewMessage); textmessage.Text = "User Name or Password is incorrect. Login with correct user name and password."; } }