How to Keep ArrayList Value When Changing Activity in Android

Question

This is ViewActivity

public class ViewActivity extends AppCompatActivity {

    private ListView lvPerson;
    private PersonListAdapter adapter;
    public List<Person> mPersonList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view);

        lvPerson = (ListView)findViewById(R.id.listView);

        //Add new person
        Intent intent = getIntent();
        if(intent.hasExtra("add")){
            String name = intent.getStringExtra("name");
            String email = intent.getStringExtra("email");
            String address = intent.getStringExtra("address");
            mPersonList.add(new Person(name, email, address));
            Toast.makeText(getApplicationContext(), "Data berhasil ditambahkan", Toast.LENGTH_SHORT).show();
        }

        //Init adapter
        adapter = new PersonListAdapter(getApplicationContext(), mPersonList);
        lvPerson.setAdapter(adapter);

    }
}

This is InputActivity

public class InputActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_input);
    }

    public void saveButtonClicked(View view){

        EditText name = (EditText) findViewById(R.id.editTextName);
        EditText email = (EditText) findViewById(R.id.editTextEmail);
        EditText address = (EditText) findViewById(R.id.editTextAddress);

        String strName = name.getText().toString();
        String strEmail = email.getText().toString();
        String strAddress = address.getText().toString();

        Intent intent = new Intent(this, ViewActivity.class);
        intent.putExtra("add", true);
        intent.putExtra("name", strName);
        intent.putExtra("email", strEmail);
        intent.putExtra("address", strAddress);
        startActivity(intent);

    }
}

Show my flow is when save button clicked in InputActivity, it will run "add person" code in ViewActivity and add data from form to ArrayList.

That's work, but when i changing activity using intent and i back to ViewActivity, ArrayList data gone.

What i want is to keep all value that i've already input in InputActivity.

Hope you understand what i mean :)

Do you want to preserve it indefinitely, or just within a single app session? — Tyler V, Jul 15 '18 at 02:15
but the problem is when i start new activity, the ArrayList data gone. I'm so stack, i have no idea with android. btw, this is my school task. this is the first time i learn Android @TylerV — Dimas Adi Andrea, Jul 15 '18 at 03:14
Thanks for the clarification. There are a lot of good answers here about passing data back and forth between activities. I added one with a different approach. — Tyler V, Jul 15 '18 at 03:19

Tyler V · Accepted Answer · 2018-07-15T03:26:52.867

There are some good answers here, but since you only want it to persist during one app session I'll add another approach, a singleton to hold the data:

class DataHolder {
    final List<Person> people = new ArrayList<>;

    private DataHolder() {}

    static DataHolder getInstance() {
        if( instance == null ) {
            instance = new DataHolder();
        }
        return instance;
    }

    private static DataHolder instance;
}

In either activity (or any place in your app), you can access the person list with

List<Person> ppl = DataHolder.getInstance().people;

For example, you would replace

public List<Person> mPersonList = new ArrayList<>();

with

// not sure why that was public...
private List<Person> mPersonList = DataHolder.getInstance().people;

It will only last for your current app session, but if you wanted to save them in the future you could add a backend database to the DataHolder so that every time you added a person it was automatically saved somewhere.

Brilliant!! this is totally works and very simple. big thanks from me. you save my live from getting D score :) — Dimas Adi Andrea, Jul 15 '18 at 03:27

Muhammad Ibrahim · Answer 2 · 2018-07-15T02:35:16.963

Override onSaveInstanceState(Bundle) in InputActivity to save whatever data you want then override onRestoreInstanceState(Bundle) in the same activity to get the values back. Using Bundle, you can store pretty much any data that you want. I'd recommend something like this:

public class ViewActivity extends AppCompatActivity {

private ListView lvPerson;
private PersonListAdapter adapter;
public List<Person> mPersonList = new ArrayList<>();

@Override 
protected void onSaveInstanceState (Bundle outState) { 
    outState.putStringArrayList("mPersonList", mPersonList); //I assume you want to mPersonList
}

@Override
protected void onRestoreInstanceState (Bundle savedInstanceState) {
    this.mPersonList = savedInstanceState.getStringArrayList("mPersonList"); //on coming back retrieve all values using key
        }

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_view);

    lvPerson = (ListView)findViewById(R.id.listView);

    //Add new person
    Intent intent = getIntent();
    if(intent.hasExtra("add")){
        String name = intent.getStringExtra("name");
        String email = intent.getStringExtra("email");
        String address = intent.getStringExtra("address");
        mPersonList.add(new Person(name, email, address));
        Toast.makeText(getApplicationContext(), "Data berhasil ditambahkan", Toast.LENGTH_SHORT).show();
    }

    //Init adapter
    adapter = new PersonListAdapter(getApplicationContext(), mPersonList);
    lvPerson.setAdapter(adapter);

}
}

The problem is in ViewActivity when i add the data to ArrayList. I'ts added, but when i changing activity the data will gone — Dimas Adi Andrea, Jul 15 '18 at 02:24
Then you should override these two added method in ViewActivity. Let me show you how. — Muhammad Ibrahim, Jul 15 '18 at 02:25
But i use "List" when declare ArrayList "public List mPersonList = new ArrayList<>();" it's give me error. Do you knom how to fix that? — Dimas Adi Andrea, Jul 15 '18 at 03:08
Dear @DimasAdiAndrea List is an interface, ArrayList is a class that implements List, among several other interfaces(ArrayList class also implements Serializable, So I would recommend to use ArrayList — Muhammad Ibrahim, Jul 15 '18 at 03:13
Moreever the main Idea is to override two methods to save data and retrieve it back. You can o tweaks to imlpement it as per your requirements — Muhammad Ibrahim, Jul 15 '18 at 03:15

Jackey · Answer 3 · 2018-07-15T02:27:43.803

What you're doing is actually very very bad, since you're just creating Activity after Activity for each Person you want to add and create. It wastes memory and power.

Instead, what you should look for is simply to return the results from InputActivity back to ViewActivity.

In your ViewActivity, don't call startActivity(intent), instead use startActivityForResult(intent, REQUEST_CODE). Then override onActivityResult() so you can handle the results that are returned back to ViewActivity.

In InputActivity, don't call startActivity() instead, return the intent back to the ViewActivity.

An example of this is like so:

ViewActivity

public class ViewActivity extends AppCompatActivity {

    private ListView lvPerson;
    private PersonListAdapter adapter;
    public List<Person> mPersonList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view);

        lvPerson = (ListView)findViewById(R.id.listView);

        //Init adapter
        adapter = new PersonListAdapter(getApplicationContext(), mPersonList);
        lvPerson.setAdapter(adapter);

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if(resultCode == RESULT_OK){
            String name = data.getStringExtra("name");
            String email = data.getStringExtra("email");
            String address = data.getStringExtra("address");
            mPersonList.add(new Person(name, email, address));
            adapter.notifyDataSetChanged();
            Toast.makeText(getApplicationContext(), "Data berhasil ditambahkan", Toast.LENGTH_SHORT).show();
        }
    }

}

InputActivity

public class InputActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_input);
    }

    public void saveButtonClicked(View view){

        EditText name = (EditText) findViewById(R.id.editTextName);
        EditText email = (EditText) findViewById(R.id.editTextEmail);
        EditText address = (EditText) findViewById(R.id.editTextAddress);

        String strName = name.getText().toString();
        String strEmail = email.getText().toString();
        String strAddress = address.getText().toString();

        Intent intent = new Intent();
        intent.putExtra("add", true);
        intent.putExtra("name", strName);
        intent.putExtra("email", strEmail);
        intent.putExtra("address", strAddress);
        setResult(RESULT_OK, intent);
        finish();    
    }
}

Doing it this way avoids recreating ViewActivity again so you don't have to recreate all the views and repopulate the lists. You simply reuse the existing ViewActivity and add the results to the existing list.

score 1 · Answer 4 · answered Jul 15 '18 at 02:22

If i understand you correctly, your flow is the following: 1.) ViewActivity -> Intent -> InputActivity 2.) InputActivity -> Intent -> ViewActivity

If that is the case, you should read more about the "Activity Lifecycle" in Android: https://developer.android.com/guide/components/activities/activity-lifecycle

In short: onCreate only gets called at the creation of the ViewActivity. If you go from there to the InputActivity and then back -> ViewActivity already exists and therefore oncreate does not get called.

One solution which comes to my mind for your case is startActivityForResult. Here an example on how to use it: How to manage `startActivityForResult` on Android?

Another general tip, as it seems that you are fairly new to android development: Use breakpoints and Log (https://developer.android.com/reference/android/util/Log) heavily to get a better feeling where and when things are happening. And do not only use tutorials to start development in Android. It does not hurt to read some beginners guide/book that explains some android specifics in more detail (like the Activity-Lifecycle)

score 0 · Answer 5 · answered Jul 15 '18 at 02:06

0

You can serialize it as a string, using Gson/Jackson/or whatever, and then save it with [SharedPreferences][1]. And then in the new activity you just load it back from SharedPreferences.

answered Jul 15 '18 at 02:06

Maxime Claude

965
12
27

While this would technically work, android already gives you the ability to save the state of and activity with `onSaveInstanceState` and `onRestoreInstanceState` – tyczj Jul 15 '18 at 02:20
he is trying to pass a class between two activities. At least this is what I have understood of his question, I might be wrong. – Maxime Claude Jul 15 '18 at 02:32

How to Keep ArrayList Value When Changing Activity in Android

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