Quick Start with Sync - Java SDK
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Tip
This Guide uses Device Sync
This guide helps you get started with an Android application that communicates with an App backend. The App provides features like Sync, Realm Functions, and user management. If your application requires only local database functionality, check out the Quick Start (Local-only) guide.
This page contains information to quickly get Atlas App Services integrated into your app. Before you begin, ensure you have:
Initialize Realm
Before you can use Realm in your app, you must initialize the Realm library. Your application should initialize Realm just once each time the application runs.
To initialize the Realm library, provide an Android
context to the Realm.init() static function. You can provide
an Activity, Fragment, or Application context for initialization with no
difference in behavior. You can initialize the Realm library
in the onCreate() method of an application subclass to
ensure that you only initialize Realm once each time the
application runs.
Tip
Register Your Application Subclass in the Android Manifest
If you create your own Application subclass, you must add it to your
application's AndroidManifest.xml to execute your custom
application logic. Set the android.name property of your manifest's
application definition to ensure that Android instantiates your Application
subclass before any other class when a user launches your application.
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.mongodb.example"> <application android:name=".MyApplicationSubclass" ... /> </manifest>
Initialize the App
To use App Services features such as authentication and sync, you must access your App using your App ID. You can find your App ID in the App Services UI.
Note
Android Studio Errors?
If Android Studio does not recognize the Realm, App, or
AppConfiguration types, there could be a problem with the
your Gradle build configuration. To fix the issue:
Clean your project with
Build > Clean ProjectRebuild your project based on your updated
build.gradlefile withBuild > Rebuild ProjectRevisit the Install the Java SDK guide to make sure that you installed the dependencies correctly.
Define Your Object Model
Your application's data model defines the structure of data stored within Realm Database and synchronized to and from App Services. You can define your application's data model in two ways:
Via schemas in App Services.
Via Kotlin or Java classes in your application code with Realm Object Models.
This quick start uses the latter approach, which defines your schema using classes in your mobile application code. To define your App's object model in this way, you need to enable Development Mode.
Once you've enabled Development Mode, add the following class definitions to your application code:
Tip
See also:
See Configure Your Data Model for more information on Realm Schema, object models, and Developer Mode.
Authenticate a User
When you have enabled anonymous authentication in the App Services UI, users can immediately log into your app without providing any identifying information:
Realm provides many additional ways to authenticate, register, and link users.
Tip
See also:
Open a Realm
Once you have enabled Sync and authenticated a
user, you can open a synced realm. Use
SyncConfiguration to control the specifics of how your application
synchronizes data with App Services, including timeouts, synchronous
reads and writes on the UI thread, and more.
Tip
See also:
Create, Read, Update, and Delete Objects
Once you have opened a realm, you can modify the objects within that realm in a write transaction block.
Important
Synchronous Reads and Writes on the UI Thread
By default, you can only read or write to a realm in your
application's UI thread using
asynchronous transactions. That is,
you can only use Realm methods whose name ends with the word
Async in the main thread of your Android application unless you
explicitly allow the use of synchronous methods.
This restriction exists for the benefit of your application users:
performing read and write operations on the UI thread can lead to
unresponsive or slow UI interactions, so it's usually best to handle
these operations either asynchronously or in a background thread.
However, if your application requires the use of synchronous
realm reads or writes on the UI thread, you can explicitly allow
the use of synchronous methods with the following
SyncConfiguration options:
To create a new Task, instantiate an instance of the
Task class and add it to the realm in a write block:
You can retrieve a live collection of all items in the realm:
You can also filter that collection using a filter:
To modify a task, update its properties in a write transaction block:
Finally, you can delete a task by calling the deleteFromRealm()
method in a write transaction block:
Watch for Changes
You can watch a realm, collection, or object for changes by attaching a custom
OrderedRealmCollectionChangeListener with the addChangeListener()
method:
Important
Serverless Limitations
You cannot watch for changes if the data source is an Atlas serverless instance. MongoDB serverless currently does not support change streams, which are used on watched collections to listen for changes.
Log Out
Once logged in, you can log out:
Complete Example
Run the complete example by replacing the appId with your realm app ID.
If you're running this project in a fresh Android Studio project, you can
copy and paste this file into your application's MainActivity -- just
remember to:
change the package declaration so it matches your project
replace the App ID placeholder with your App's App ID
update the
importstatements forTaskandTaskStatusif you're using Java
Output
Running the above code should produce output resembling the following:
Successfully authenticated anonymously. Updated range: 0 to 1 Deleted range: 0 to 1 Successfully logged out.