[Firestore] Asynchronous methods from library hang and don't return anything.

Hello. I am trying to incorporate Cloud Firestore into a C# application. I created the async method below (and I call it from the main method of my application):

        public async Task firebaseStuff()
        {
            FirestoreDb db = FirestoreDb.Create(projectId);
            CollectionReference collection = db.Collection("users");
            QuerySnapshot allUsers = await collection.GetSnapshotAsync();
            MessageBox.Show("Done Querying!");
            return;
        }

The users collection only has one document. The GetSnapshotAsync() method doesn’t seem to return anything and the “Done Querying!” box never shows. Am I missing something?

[jskeet]

Right, the constructor itself can’t be asynchronous - but you can call a static factory method which is asynchronous, does all the async work, and then constructs an instance:

public static MainWindow CreateAsync()
{
    var doc = await CreateFirebaseDoc();
    return new MainWindow(doc);
}

I don’t know whether that will be the right solution for you or not, but it’s one option to consider.

What’s more important is that you understand why your previous code failed - by calling Wait(), you were saying “I’m not going to let the WPF dispatcher thread do anything else until the task returned by firebaseStuff has completed”. Unfortunately, the firebaseStuff method has said “When the task returned by AddAsync completes, I need to come back to the WPF Dispatcher thread in order to return and set the task result”. That’s why you’ve got a deadlock.

I’m going to close this issue now as it really isn’t related to Firestore or the client library - it’s just a matter of working correctly with async methods.

[nmggithub]

The app itself is a WPF app. I am calling the method from within the MainWindow.xaml.cs constructor which isn’t (and can’t be, to my knowledge) async. I just tried without .Wait() and it seems to have worked? I’m going to try and test it a few more ways before confirming.

EDIT: Yeah, it works. Thank you for explaining what I did wrong.