Android Data Sync

Dmytro Danylyk

Timee GmbH.

What is data synchronization?

"Data synchronization - is the process of establishing consistency among data from a source to a target data storage and vice versa and the continuous harmonization of the data over time." - Wikipedia

Download data from server

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

GCM

User Action

(pull-to-refresh)

(data on server updated)

Database

(request data from server and save to database)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

GCM

User Action

(pull-to-refresh)

(data on server updated)

Database

(request data from server and save to database)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(pull-to-refresh)

GCM

(data on server updated)

Database

(request data from server and save to database)

Sync

Database

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(pull-to-refresh)

GCM

(data on server updated)

(request data from server and save to database)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(pull-to-refresh)

GCM

(data on server updated)

Database

(request data from server and save to database)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(pull-to-refresh)

GCM

(data on server updated)

Database

(request data from server and save to database)

Upload data to server

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

Sync

User Action

(updated profile)

Database

(save data to database and upload to server)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(updated profile)

Database

(save data to database and upload to server)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

Database

(save data to database and upload to server)

User Action

(updated profile)

Sync

Event Bus

Table A was updated

Table B was updated

Table C was updated

Activity A reload data

Activity B reload data

Activity C reload data

User Action

(updated profile)

Database

(save data to database and upload to server)

Layers

User Credentials

Storage

User Interface

Sync

Communication

User Credentials Layer

Responsibilities:

  • store user credentials
  • retrieve user credentials

User Credentials Layer

Where to store user credentials?

External Storage

Not secure.

Where to store user credentials?

Preferences

External Storage

Can be cleared by user.

Where to store user credentials?

Preferences

External Storage

SQLite Databases

Can be cleared by user.

Where to store user credentials?

Preferences

Account Manager

External Storage

SQLite Databases

Why Account Manager?

  • Gives users a central point  to define their credentials via Settings - Accounts

Why Account Manager?

  • Gives users a central point  to define their credentials via Settings - Accounts
  • User data is not cleared when user Clear Cache / Clear Data

Why Account Manager?

  • Gives users a central point  to define their credentials via Settings - Accounts
  • User data is not cleared when user Clear Cache / Clear Data
  • Provide possibility to turn on Auto-sync data

Why Account Manager?

  • Gives users a central point  to define their credentials via Settings - Accounts
  • User data is not cleared when user Clear Cache / Clear Data
  • Provide possibility to turn on Auto-sync data
  • Provide settings screen where user can trigger, turn on/off sync

Account Manager usage

AccountManager accountManager = AccountManager.get(getApplicationContext());

// create new account
Account account = new Account(username, accountType)

// add account and auth token
accountManager.addAccountExplicitly(account, password, userData);
accountManager.setAuthToken(account, authTokenType, accessToken);

How to add new account ?

Account Manager usage

// to get account manager
AccountManager accountManager = AccountManager.get(getApplicationContext());

// to get account
Account[] accounts = accountManager.getAccountsByType(getAccountType(context));
Account account != null && accounts.length != 0 ? accounts[0] : null;

// to get auth token
String authToken = accountManager.peekAuthToken(account, authTokenType);

How to get account ?

Want to know more?

developers.google.com

/android/guides/http-auth

Sync Layer

Sync Layer

Responsibilities:

  • perform requests to server
  • use storage layer to cache data to storage
  • send global app events via communication layer

How to make data sync?

Thread

Runs only when application is launched.

How to make data sync?

Thread

Service

Requires writing extra logic to handle automated execution, network checking, etc.

How to make data sync?

Thread

Service

Sync Adapter

Requires ContentProvider (or StubProvider if you are not using ContentProvider).

How to make data sync?

Thread

GCM Network Manager

Service

Sync Adapter

Not possible to execute immediate Task.

How to make data sync?

GCM Network Manager

Sync Adapter

  • Schedule one-off vs. periodic tasks.
  • Awareness of network activity.
  • Awareness of device charging state.
  • Automatic back-off and failure retry.
  • Persistence of tasks across boot.

When to sync?

At regular intervals

Run a sync adapter after the expiration of an interval you choose, or run it at a certain time every day.

When to sync?

At regular intervals

When the system sends out a network message

Run a sync adapter when the Android system sends out a network message that keeps the TCP/IP connection open; this message is a basic part of the networking framework.

When to sync?

At regular intervals

When the system sends out a network message

When device data changes

Run a sync adapter when data changes on the device. This option allows you to send modified data from the device to a server, and is especially useful if you need to ensure that the server always has the latest device data.

When to sync?

At regular intervals

When the system sends out a network message

When device data changes

When server data changes

Run the sync in response to a GCM message from a server, indicating that server-based data has changed. This option allows you to refresh data from the server to the device without degrading performance or wasting battery life by polling the server.

Regular intervals sync

/*
 * Specifies that a sync should be requested with the specified the account, 
 * authority, and extras at the given frequency.
 */

 long intervalSeconds = TimeUnit.MINUTES.toSeconds(60);
 ContentResolver.addPeriodicSync(account, authority, bundle, intervalSeconds);

Sync Adapter usage

When the system sends out a network message

/*
 * Set whether or not the provider is synced when it receives a network tickle.
 */

 ContentResolver.setSyncAutomatically(account, authority, true);

Sync Adapter usage

When device data changes

/*
 * Start an asynchronous sync operation
 */

 ContentResolver.requestSync(mAccount, AUTHORITY, settingsBundle);

Sync Adapter usage

When server data changes

public class MyGcmListenerService extends GcmListenerService {

    @Override
    public void onMessageReceived(String from, Bundle data) {
        String type = data.getString("type");
        
        switch (SyncType.fromString(type)) {
            case SyncType.FEED:
                SyncAdapter.syncFeed();
                break;

            case SyncType.PROFILE:
                SyncAdapter.syncProfile();
                break;
        }
    }
}

Sync Adapter usage

Want to know more?

developer.android.com

/training/sync-adapters

Storage Layer

Storage Layer

Responsibilities:

  • save data to persistent storage
  • retireve data from persistent storage

Where to store data?

Preferences

Can be used for small amount of data.

Where to store data?

Preferences

SQLiteDatabase

  • Require a lot of extra code, unless you use ORM
  • Doesn't support lazy loading

Where to store data?

Preferences

SQLiteDatabase

Realm

  • Easy to implement
  • Fast

What is realm?

"Realm is a mobile database: a replacement for SQLite & ORMs." - realm.io

Realm usage

public class User extends RealmObject {

    @PrimaryKey
    private String name;
    private int age;

    // Standard getters & setters
}

Model

Realm usage

// Query to look for all users
RealmResults<User> result1 = realm.where(User.class).findAll();

// Query with conditions
RealmResults<User> result2 = realm.where(User.class)
                                  .equalTo("name", "John")
                                  .or()
                                  .equalTo("name", "Peter")
                                  .findAll();

Read

Realm usage

User user = new User("John");
user.setEmail("john@corporation.com");

// Copy the object to Realm. Any further changes must happen on realmUser
realm.beginTransaction();
realm.copyToRealm(user);  
realm.commitTransaction();

Write

Realm usage

private void reloadData() {
    // new thread
    new Thread(new Runnable() {
        @Override
        public void run() {
            // switch to ui thread
            List<User> userList = UserDAO.newInstance().getAll();
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mAdapter.setData(userList);
                }
            });
        }
    }).start();
}

SQLite data loading flow

Realm usage

private void loadData() {
    // ui thread, because query of 5000 objects takes around 4 ms
    mAdapter.setData(UserDAO.newInstance().getAll());
}

private void reloadData() {
    // no need to reload data, since realm result
    // represent all changes made in table
    mAdapter.notifyDataSetChanged();
}

Realm data loading flow

Want to know more?

realm.io/docs/java/latest

Communication Layer

Communication Layer

Responsibilities:

  • deliver global app events

How to deliver global app events?

Local Broadcast

Require extra code to store / retrieve data from intent

How to deliver global app events?

Local Broadcast

Event Bus

Simplifies the communication between components

What is event bus?

"EventBus - allows publish-subscribe-style communication between components without requiring the components to explicitly register with one another (and thus be aware of each other)"

Greenrobot usage

public class SyncEvent {

    private Type mType;
    private Status mStatus;
    
    // Additional fields if needed
}

Define event

Greenrobot usage

public class MyActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventBus.getInstance().register(this);
    }

}

Subscribe to event

Greenrobot usage

public class MyActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventBus.getInstance().register(this);
    }

    @Override
    protected void onDestroy() {
        EventBus.getInstance().unregister(this);
        super.onDestroy();
    }

}

Subscribe to event

Greenrobot usage

public class MyActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventBus.getInstance().register(this);
    }

    @Override
    protected void onDestroy() {
        EventBus.getInstance().unregister(this);
        super.onDestroy();
    }

    public void onEvent(SyncEvent event) {
        if(event.mType == Type.PROFILE) {
            if(event.mStatus == Status.COMPLETED) {
                // reload UI
            }
        }
    }

}

Subscribe to event

Greenrobot usage

public class Sync {
    
    protected void doProfileSync() {
        EventBus.getInstance().post(new SyncEvent(Type.Profile, Status.IN_PROGRESS));
        // sync logic
        EventBus.getInstance().post(new SyncEvent(Type.Profile, Status.COMPLETED));
    }

}

Fire event

Want to know more?

github.com

/greenrobot/EventBus

User Interface Layer

User Interface Layer

Responsibilities:

  • display data
  • use storage layer to retrieve data from storage
  • listen to global app events from communication layer

Upload data to server

void onSaveClicked(User user) {
    UserProfileDAO.update(user);
    SyncAdapter.syncProfile();
}
void update(User user) {
    realm.beginTransaction();
    realm.copyToRealmOrUpdate(user);  
    realm.commitTransaction();
}

User Interface

Storage

void syncProfile() {
    sendProfileEvent(Status.IN_PROGRESS);
    doGet();
    doPost(UserProfileDAO.getModified());
    sendProfileEvent(Status.COMPLETED);
}
void onSaveClicked(User user) {
    UserProfileDAO.update(user);
    SyncAdapter.syncProfile();
}
void update() {
    realm.beginTransaction();
    realm.copyToRealmOrUpdate(user);  
    realm.commitTransaction();
}

User Interface

Storage

Sync

RealmResults<User> getModified() {
    return 
        realm.where(User.class)
        .equalTo("isModified", true)
        .findAll();
}

Storage

void syncProfile() {
    sendProfileEvent(Status.IN_PROGRESS);
    doGet();
    doPost(UserProfileDAO.getModified());
    sendProfileEvent(Status.COMPLETED);
}
void onSaveClicked(User user) {
    UserProfileDAO.update(user);
    SyncAdapter.syncProfile();
}
void update() {
    realm.beginTransaction();
    realm.copyToRealmOrUpdate(user);  
    realm.commitTransaction();
}

User Interface

Storage

Sync

RealmResults<User> getModified() {
    return 
        realm.where(User.class)
        .equalTo("isModified", true)
        .findAll();
}

Storage

public void onEvent(SyncEvent e) {
    if(e.type == Type.PROFILE
            && e.status == Status.COMPLETED) {
            // reload UI
        }
    }
}

User Interface

Communication

void sendProfileEvent(Status s) {
    EventBus.getInstance.send(
        new SyncEvent(Type.Profile, s);
    );
}

Download data from server

void onPullToRefresh() {
    SyncAdapter.syncProfile();
}

User Interface

void syncProfile() {
    sendProfileEvent(Status.IN_PROGRESS);
    doGet();
    doPost(UserProfileDAO.getModified());
    sendProfileEvent(Status.COMPLETED);
}
void onPullToRefresh() {
    SyncAdapter.syncProfile();
}

User Interface

Sync

RealmResults<User> getModified() {
    return 
        realm.where(User.class)
        .equalTo("isModified", true)
        .findAll();
}

Storage

void syncProfile() {
    sendProfileEvent(Status.IN_PROGRESS);
    doGet();
    doPost(UserProfileDAO.getModified());
    sendProfileEvent(Status.COMPLETED);
}
void onPullToRefresh() {
    SyncAdapter.syncProfile();
}

User Interface

Sync

RealmResults<User> getModified() {
    return 
        realm.where(User.class)
        .equalTo("isModified", true)
        .findAll();
}

Storage

public void onEvent(SyncEvent e) {
    if(e.type == Type.PROFILE
            && e.status == Status.COMPLETED) {
            // reload UI
        }
    }
}

User Interface

Communication

void sendProfileEvent(Status s) {
    EventBus.getInstance.send(
        new SyncEvent(Type.Profile, s);
    );
}

F.A.Q.

"No, requests like sign in, sign up, search (if result is not cached) are performed directly in activity."

Are all application requests performed via sync?

"If user data is always considered as most recent you should do POST, then GET.

If server data is always considered as most recent you should do GET, then POST."

What to do first during sync, GET or POST?

"Add to all your data objects isModified field. When user update object in database set isModified field to true. During sync, upload all objects where isModified equals true."

Which data to upload during POST?

"Track if activity is visible in onPause / onResume methods and render screen only if data was updated and activity is visible."

Having several activities in stack which listen to the same event, cause inefficient view render.

@dmytrodanylyk

dmytrodanylyk.com

slides.com/dmytrodanylyk

S

Android Data Sync

By Dmytro Danylyk

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