AuthActivity.java

package com.example.android.mybbideal;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class AuthActivity extends AppCompatActivity {

    SharedPreferences sharedPreferences;

    String userName;
    String userPwd;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        sharedPreferences = getSharedPreferences(Constant.MyPREFERENCES,Context.MODE_PRIVATE);

        userName = sharedPreferences.getString(Constant.Name,"0");

        setContentView(R.layout.activity_auth);
        Button buttonAuth = (Button) this.findViewById(R.id.button_auth);

        if(userName.equals("0")) {
            buttonAuth.setText("Daftar");
        } else {
            buttonAuth.setText("Login");
        }

        TextView txtLupaPwd = (TextView) this.findViewById(R.id.text_lupa_pwd_login);

        txtLupaPwd.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                AuthActivity.this.finish();
                Intent intent = new Intent(AuthActivity.this, ForgotPwdActivity.class);
                AuthActivity.this.startActivity(intent);
            }
        });

        EditText editUsername = (EditText) findViewById(R.id.username);
        EditText editPassword = (EditText) findViewById(R.id.password);

        if (savedInstanceState == null) {
            Bundle extras = getIntent().getExtras();
            if(extras == null) {
                // do nothing
            } else {
                editUsername.setText( extras.getString("extraUser"));
                editPassword.setText( extras.getString("extraPwd") );
            }
        }
    }

    public void prosesAuth(View view) {
        EditText editUsername = (EditText) findViewById(R.id.username);
        EditText editPassword = (EditText) findViewById(R.id.password);

        String u = editUsername.getText().toString();
        String p = editPassword.getText().toString();

        Button btnBtn = (Button) this.findViewById(R.id.button_auth);
        if( btnBtn.getText().toString().equals("Daftar") ) {
            SharedPreferences.Editor editor = sharedPreferences.edit();

            editor.putString(Constant.Name, u);
            editor.putString(Constant.Pwd, p);
            editor.apply();

            goToActivity(MainActivity.class);
        } else  {
            userName = sharedPreferences.getString(Constant.Name,"0");
            userPwd = sharedPreferences.getString(Constant.Pwd,"0");

            if( u.equals(userName) && p.equals(userPwd) ) {
                goToActivity(MainActivity.class);
            } else {
                Toast.makeText(this, "Invalid username/password!", Toast.LENGTH_SHORT).show();
            }
        }
    }
    public void goToActivity(Class act) {
        this.finish();
        Intent intent = new Intent(this,act);
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        this.startActivity(intent);
    }
}