Passing an arraylist of arraylists

Question

I know it\'s a commonly asked question and I looked at the solutions online, but I am having a difficulty implementing this on my own.

I have a class which contains thr

Answer 1

I think the best thing to do here would be to create a new class that implements Parcelable and pass instances of this new class between activities.

public class ParcelableListOfLists implements Parcelable {

    private ArrayList<ArrayList<imageHolder>> listOfLists;

    public ParcelableListOfLists(ArrayList<ArrayList<imageHolder>> listOfLists) {
        this.listOfLists = listOfLists;
    }

    public ArrayList<ArrayList<imageHolder>> getListOfLists() {
        return listOfLists;
    }

    // parcelable implementation here
}

Once you have this class, you can be in full control of how your data is parceled, and that lets you do some things that you won't be able to do with the Android built-in offerings.

Here's one way you could parcel a list of lists:

@Override
public void writeToParcel(Parcel dest, int flags) {
    if (listOfLists != null) {
        dest.writeInt(listOfLists.size());

        for (ArrayList<imageHolder> list : listOfLists) {
            dest.writeTypedList(list);
        }
    } else {
        dest.writeInt(-1);
    }
}

And on the other side, you can recreate the list of lists like this:

public ParcelableListOfLists(Parcel in) {
    int size = in.readInt();

    if (size != -1) {
        this.listOfLists = new ArrayList<>(size);

        for (int i = 0; i < size; ++i) {
            ArrayList<imageHolder> list = in.createTypedArrayList(imageHolder.CREATOR);
            listOfLists.add(list);
        }
    } else {
        this.listOfLists = null;
    }
}

With all of this together, you can pass your list of lists between activities like this:

Intent nextActivity = new Intent(loadImages.this, storiesScreen.class);
nextActivity.putExtra("images", new ParcelableListOfLists(images));
startActivity(nextActivity);

and retrieve them in the next activity like this:

ParcelableListOfLists plol = getIntent().getParcelableExtra("images");
ArrayList<ArrayList<imageHolder>> images = plol.getListOfLists();

Answer 2

Ok.

Your Model

public class ImageHolder implements Serializable {

    // Use String here, to avoid serialization problems
    private String uri;
    private Date date;
    private Location loc;

    public ImageHolder() {
    }

    public ImageHolder(String uri, Date date, Location loc) {
        this.uri = uri;
        this.date = date;
        this.loc = loc;
    }

    public String getUri() {
        return uri;
    }

    public void setUri(String uri) {
        this.uri = uri;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public Location getLoc() {
        return loc;
    }

    public void setLoc(Location loc) {
        this.loc = loc;
    }

    @Override
    public String toString() {
        return "ImageHolder{" +
                "uri=" + uri +
                ", date=" + date +
                ", loc=" + loc +
                '}';
    }
}

Create a Container class

public class Container implements Serializable {

    private ArrayList<ImageHolder> list;

    public Container() {
    }

    public Container(ArrayList<ImageHolder> list) {
        this.list = list;
    }

    public ArrayList<ImageHolder> getList() {
        return list;
    }

    public void setList(ArrayList<ImageHolder> list) {
        this.list = list;
    }

    @Override
    public String toString() {
        return "Container{" +
                "list=" + list +
                '}';
    }
}

Your First Activity

public class MainActivity extends AppCompatActivity {

    public static final String TAG = MainActivity.class.getSimpleName();

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

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

        ImageHolder imageHolder0 = new ImageHolder("http://www.stackoverflow.com", new Date(), new Location("test0"));
        ImageHolder imageHolder1 = new ImageHolder("http://www.google.com", new Date(), new Location("test1"));

        ArrayList<ImageHolder> list = new ArrayList<>();
        list.add(imageHolder0);
        list.add(imageHolder1);

        Container container = new Container(list);

        Gson gson = new Gson();
        String json = gson.toJson(container);

        Intent intent = new Intent(MainActivity.this, TestActivity.class);
        intent.putExtra("yourKey", json);

        startActivity(intent);
    }
}

Your second activity

public class TestActivity extends AppCompatActivity {
    public static final String TAG = TestActivity.class.getSimpleName();

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

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

        Gson gson = new Gson();
        Container container = gson.fromJson(getIntent().getStringExtra("yourKey"), Container.class);

        Log.d(TAG, "OK?" + container.getList().toString());

        // Here convert String uri Fields to Uri Objects
        // Example:
        Uri uri = Uri.parse(container.getList().get(0).getUri());
    }
}

Logcat result: 08-01 11:10:22.097 6671-6671/it.darksurfer.english.template D/TestActivity: OK?[ImageHolder{uri=http://www.stackoverflow.com, date=Wed Aug 01 11:10:21 GMT+02:00 2018, loc=Location[test0 0,000000,0,000000 acc=??? t=?!? et=?!?]}, ImageHolder{uri=http://www.google.com, date=Wed Aug 01 11:10:21 GMT+02:00 2018, loc=Location[test1 0,000000,0,000000 acc=??? t=?!? et=?!?]}]

Obviously you can put an undefined number of others ArrayList in the list of Container class!

Answer 3

I think that you can use Gson too.

In your build.gradle

implementation 'com.google.code.gson:gson:2.8.4'

In the first activity

Gson gson = new Gson();
String json = gson.toJson(yourObject);
intent.putExtra("yourKey", json);

In the second activity

Gson gson = new Gson();
YourObject yourObject = gson.fromJson(getIntent().getStringExtra("yourKey"), YourObject.class);

Easy and fast.