MainActivity.java

package com.example.ya_.myapplication;
/*summber:https://github.com/itb-prd/membuat-aplikasi-android-dasar-yonasadiel*/
import android.app.DialogFragment;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    public ArrayList<String> ToDoListContent = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        readFromFile();

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent getNewNameIntent = new Intent(view.getContext(), addScreen.class);
                final int result = 2;

                startActivityForResult(getNewNameIntent, result);
            }
        });

       displayList();

    }

    protected void displayList() {
        ListAdapter theAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, ToDoListContent);

        ListView theListView = (ListView) findViewById(R.id.ToDoListView);

        theListView.setAdapter(theAdapter);

        theListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, final int position, long id) {

                DialogFragment newFragment = editDialog.newInstance(position,ToDoListContent.get(position));
                newFragment.show(getFragmentManager(),"dialog");
                displayList();
            }
        });

        saveIntoFile();
    }

    private void readFromFile() {
        String filename = "todolistfile.dat";

        try {
            FileInputStream ins = new FileInputStream(new File(getFilesDir(), filename));
            BufferedReader br = new BufferedReader(new InputStreamReader(ins));

            String todo;

            while((todo = br.readLine()) != null) {
                ToDoListContent.add(todo);
            }
            br.close();
        } catch (Exception e){
            e.printStackTrace();
        }
    }

    private void saveIntoFile() {
        String filename = "todolistfile.dat";

        try {
            PrintWriter pw = new PrintWriter(new FileOutputStream(new File(getFilesDir(), filename)));
            for (String todo: ToDoListContent) {
                pw.println(todo);
            }
            pw.close();
        } catch (Exception e){
            e.printStackTrace();
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == 1 && data != null) {
            int index = data.getExtras().getInt("Index of ToDoList");
            ToDoListContent.set(index,data.getExtras().getString("New Name"));
            displayList();
        } else if (requestCode == 2 && data != null) {
            ToDoListContent.add(data.getExtras().getString("New Task"));
            displayList();
        } else if (requestCode == 3 && data != null) {
            ToDoListContent.remove(data.getExtras().getInt("Index of ToDoList"));
            displayList();
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.about_page) {
            DialogFragment Fragment = new AboutDialog();
            Fragment.show(getFragmentManager(),"theDialog");

            return true;
        } else if (id == R.id.exit_the_app) {
            finish();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

}