Android State - save and restore activity's state in a bundle

!!save_activity_state.md

Saving and restoring activity state across configuration changes

1. implement onSaveInstanceState(Bundle state)
2. implement onRestoreInstanceState(Bundle state)

• input controlls are saved automatically
• listview items/position etc need to be saved.
• to persist for the long term use SQLite db, shared prefrences or a file

MainActivity.java

package com.example.user.arrayadapter1;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private ArrayAdapter<Person> listAdapter;
    private ListView listView;
    private EditText editText;
    private ArrayList<Person> people;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button) findViewById(R.id.addButton);
        button.setOnClickListener(this);

        // Creating a list of initialization data for the list view
        // We're using composite objects - Person
        people = new ArrayList();
        people.add(new Person("Eli", 10));
        people.add(new Person("Dani", 11));
        people.add(new Person("Rani", 12));

        // Creating an array adapter (INIT DATA IS SUPPLIED AT THE END OF THE LINE)
        // The title of each item in the listview, is decided by the value a Person's toString() method
        // The listview calls the toString() method of its items, and uses the returned string as
        // the name of the item in the list
        listAdapter = new ArrayAdapter<Person>(this, android.R.layout.simple_list_item_1, people);

        // Connecting the array adapter to the listview
        listView = (ListView) findViewById(R.id.listView);
        listView.setAdapter(listAdapter);

//        this.editText = (EditText) findViewById(R.id.editText1);

        // Registering the list view to a single short click event (callback)
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Person person = (Person) parent.getItemAtPosition(position);
                Toast.makeText(getApplicationContext(), person.getName()+ " " + person.getAge(), Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    public void onClick(View view) {

        // Getitng a reference to the UI item where the user write names
        TextView textView = (TextView) findViewById(R.id.editText1);

        // Extracting the name the user wrote
        String name = textView.getText().toString();

        // Creating a person (hard coded age - 20)
        Person person = new Person(name, 20);

        // Adding the user to the names list (ArrayList)
        people.add(person);

        // Clearing the area where the user writes
        textView.setText("");

        // Updating the list (a classing Model - View interaction + Observer design pattern)
        listAdapter.notifyDataSetChanged();
    }

    @Override
    public void onSaveInstanceState(Bundle state) {
        super.onSaveInstanceState(state);
        state.putSerializable("people", people);
    }

    @Override
    public void onRestoreInstanceState(Bundle state) {
        super.onRestoreInstanceState(state);
        this.people.clear();
        this.people.addAll((ArrayList<Person>) state.getSerializable("people"));
        this.listAdapter.notifyDataSetChanged();
    }
}

Person.java

package com.example.user.arrayadapter1;

import java.io.Serializable;

public class Person implements Serializable{

    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return this.name;
    }
}

Thanks

Great