How to use Realm Collection Notifications in an ASP.NET Core Application? - asp.net-core

Question

I've tried using this sample code from the Realm .NET SDK but my handler code never gets called consistently:
var token = realm.All<Person>().SubscribeForNotifications ((sender, changes, error) =>
{
// Access changes.InsertedIndices, changes.DeletedIndices, and changes.ModifiedIndices
});
I've tried running this from a number of different threads, but I suspect none of them have a looper/runloop, a requirement noted in the SDK. Is it even possible to create a looper/runloop thread in ASP.NET Core that will work with Realm? How would I do that?

Answer 1

Finally figured out how to implement the looper/run loop that works for Realm Notifications. The keys parts of the solution are:
Use a hosted service to start/stop the thread.
Use Nito.AsyncEx to establish a synchronization context for that thread.
Loop inside the thread, calling the RefreshAsync method on the realm instance.
Call Task.Delay between loop iterations to keep the thread cpu-friendly.
Here is the code:
public class RealmNotificationService : IHostedService
{
private System.Threading.Thread _thread;
public Task StartAsync(CancellationToken stoppingToken)
{
_thread = new System.Threading.Thread(() =>
Nito.AsyncEx.AsyncContext.Run(() => Looper(stoppingToken))
);
_thread.Start();
return Task.CompletedTask;
}
public Task StopAsync(CancellationToken stoppingToken)
{
return Task.CompletedTask;
}
private async void Looper(CancellationToken stoppingToken)
{
using (var connection = await Realm.GetInstanceAsync({YOUR-CONFIG}))
{
var token = connection.All<{YOUR-OBJECT}>().SubscribeForNotifications((sender, changes, error) =>
{
// Access changes.InsertedIndices, changes.DeletedIndices, and changes.ModifiedIndices
});
}
while (!stoppingToken.IsCancellationRequested)
{
await connection.Realm.RefreshAsync();
await Task.Delay(2000, stoppingToken);
}
}
}

Answer 2

Bill Raudabaugh's answer almost worked for me. However, the final while loop is outside of the using so connection is undefined.
I was able to get it to work by moving that loop inside of the using. Also I removed the RefreshAsync() as it seems it's not needed; Realm automatically updates in real time without having to refresh.
Here is my code:
public class RealmNotificationService : IHostedService
{
private System.Threading.Thread _thread;
public Task StartAsync(CancellationToken stoppingToken)
{
_thread = new System.Threading.Thread(() =>
Nito.AsyncEx.AsyncContext.Run(() => Looper(stoppingToken))
);
_thread.Start();
return Task.CompletedTask;
}
public Task StopAsync(CancellationToken stoppingToken)
{
return Task.CompletedTask;
}
private async void Looper(CancellationToken stoppingToken)
{
using (var connection = await Realm.GetInstanceAsync({YOUR-CONFIG}))
{
var token = connection.All<{YOUR-OBJECT}>().SubscribeForNotifications((sender, changes, error) =>
{
// Access changes.InsertedIndices, changes.DeletedIndices, and changes.ModifiedIndices
});
while (!stoppingToken.IsCancellationRequested)
{
await Task.Delay(2000, stoppingToken);
}
}
}
}