Configure & Open a Synced Realm - .NET SDK

Synced Realms vs. Non-Synced Realms

Synced realms differ from non-synced local Realm in a couple of ways:

• Synced realms attempt to sync changes with your backend App Services App, whereas non-synced realms do not.

• Synced realms can be accessed by authenticated users, while non-synced realms have no concept of users or authentication.

You can copy data from a non-synced realm to a synced realm, and vice versa, but you cannot sync a non-synced realm.

Synced Realms

To open a synced realm, you must have an authenticated User object. To obtain an initial User instance, you need to authenticate against the Atlas App Services backend, which requires the device to be online the first time a user logs in. Once initial authentication has occurred, you can retrieve an existing user while offline.

Open a Synced Realm While Online

The steps for opening a synced realm while online are:

1. Your app code walks the user through authenticating.

2. Create a FlexibleSyncConfiguration object that includes User object.

3. Open a synced realm by calling the GetInstanceAsync() method.

4. If your FlexibleSyncConfiguration did not contain initial subscriptions, add a subscription.

The following code demonstrates these steps:

var app = App.Create("myRealmAppId");
var user = await app.LogInAsync(Credentials.Anonymous());
Realm realm;
var config = new FlexibleSyncConfiguration(user)
{
    PopulateInitialSubscriptions = (realm) =>
    {
        var allTasks = realm.All<MyTask>();
        realm.Subscriptions.Add(allTasks, new SubscriptionOptions { Name = "allTasks" });
    }
};
try
{
    realm = await Realm.GetInstanceAsync(config);
}
catch (Exception ex)
{
    Console.WriteLine($@"Error creating or opening the
        realm file. {ex.Message}");
}

In the above example, the code shows how to open the realm asynchronously by calling GetInstanceAsync(). You can also open a realm synchronously by calling the GetInstance() method:

var synchronousRealm = Realm.GetInstance(config);

Open a Synced Realm While Offline

Once a user authenticates, the User object persists on the device until the user logs off. This allows your app to retrieve an existing user and open a synced realm in an offline state. Changes that occur while offline will be synced by the SDK once the device reconnects to your App.

The following code shows how to check if there is an existing User object. If none is found, it uses the process outlined about to obtain a user. If the device already has a user, it opens the synced realm with that user:

var app = App.Create("myRealmAppId");
Realms.Sync.User user;
FlexibleSyncConfiguration config;
Realm realm;
if (app.CurrentUser == null)
{
    // App must be online for user to authenticate
    user = await app.LogInAsync(Credentials.Anonymous());
    config = new FlexibleSyncConfiguration(user);
    realm = Realm.GetInstance(config);
    // Go on to add or update subscriptions and use the realm
}
else 
{
    // This works whether online or offline
    // It requires a user to have been previously authenticated
    user = app.CurrentUser;
    config = new FlexibleSyncConfiguration(user);
    realm = Realm.GetInstance(config);
    // Go on to add or update subscriptions and use the realm
}

Configuring Timeouts with AppConfiguration

For granular control of your app connection, you can set the SyncTimeoutOptions on the AppConfiguration object. You can set the following Sync timeout properties:

• ConnectTimeout: the amount of time to allow for a connection to become fully established.

• ConnectionLingerTime: the amount of time to keep a connection open after all sessions have been abandoned.

• PingKeepAlivePeriod: the amount of time between each heartbeat ping message

• PongKeepAliveTimeout: the amount of time to wait for a response to a heartbeat ping before concluding that the connection has dropped.

• FastReconnectLimit: the amount of time since the loss of a previous connection for a new connection to be considered a "fast reconnect".

AppConfiguration configuration = new AppConfiguration("myRealmAppId")
{
    SyncTimeoutOptions = new SyncTimeoutOptions()
    {
        ConnectTimeout = TimeSpan.FromMinutes(2),
        ConnectionLingerTime = TimeSpan.FromSeconds(30),
        PingKeepAlivePeriod = TimeSpan.FromMinutes(1),
        PongKeepAliveTimeout = TimeSpan.FromMinutes(1),
        FastReconnectLimit = TimeSpan.FromMinutes(1),
    },
};