Question How to have multiple Firebase AddSnapshotListener(s) inside a single class?

[VivekScorp]

I have a class in android which has a listener setup to get visitorlist updates.

var visitorDetailsCollection = FirebaseFirestore.Instance.Collection("visitorDetails");
            var visitorDetailsquery = visitorDetailsCollection.WhereEqualTo("UserID", Firebase.Auth.FirebaseAuth.Instance.CurrentUser.Uid);
            visitorlistner = visitorDetailsquery.AddSnapshotListener(this);

and when the firestore db is updated the following method runs and gets the updates

public void OnEvent(Java.Lang.Object obj, FirebaseFirestoreException error)
{
try
            {
                var docs = (QuerySnapshot)obj;
                visitorDetails.Clear();
                foreach (var doc in docs.Documents)
                {
                        var visitordetails = new VisitorDetails
                        {
                            Name = doc.Get("VisitorName").ToString(),
                            ContactNumber = doc.Get("VisitorContact").ToString(),
                            VehicleNumber = doc.Get("VisitorVehicleNo").ToString(),
                            IsApproved = doc.Get("VisitorIsApproved").ToString(),
                            IsActive = doc.Get("VisitorIsActive").ToString(),
                            Purpose = doc.Get("PurposeOfVisit").ToString(),
                            Email = doc.Get("VisitorEmail").ToString(),
                            FromDate = toDatetime(doc.GetDate("FromDate") as Date),
                            ToDate = toDatetime(doc.GetDate("ToDate") as Date),
                            docID = doc.Id
                        };
                        visitorDetails.Add(visitordetails);                   
}

Now I want to add another listener to get residentdetails like this

residentlistner = residentDetailsquery.AddSnapshotListener(this);

How do I tell this listener to run a different function like

public void OnEvent2(Java.Lang.Object obj, FirebaseFirestoreException error)
{}

when the firestore db is updated?

 

[Skydiver]

The response you got in Stack Overflow is the best, cleanest approach: pass in a different instance instead of this. Any other approach, would be hacky where you need to detect the object passed into the event.

 

[VivekScorp]

but how to create a new/different instance?

 

[Skydiver]

The same way you would do would any other class. Declare a class. Call new to create an instance of that class. I don't understand why this is a difficult concept. You should have learned this as a basic part of learning how to program in any object-oriented language. I would assume that you already know how to do this considering that you are already advanced enough to be writing a mobile application. Please tell me that you aren't doing cargo-cult programming.

 

[VivekScorp]

ha ha, But that way it will again create a new instance of the same class and a new instance of the same onEvent function right?

Coz in Stackoverflow Jason asked me to create a separate instance of the listener rather than using "this"
so I asked on how to do that actually

 

[Skydiver]

No, you'll need to create an instance of a different class that also has an OnEvent() method on it.

Basically in pseudo code:

class VisitorDetailsUpdatedEventArgs : EventArgs
{
    // Properties/fields to hold visitor detail docs
    // Constructor that takes docs
}

class VisitorDetailsListener : WhatEverFirebaseBaseClassOrInterfaceNeeded
{
   :
    public event EventHandler<VisitorDetailsUpdateEventArgs> VisitorDetailsUpdated;

    public void OnEvent(Java.Lang.Object obj, FirebaseFirestoreException error)
    {
        // your code here that extracts visitor details docs

        // Notify event listeners the C# way, rather than the Java way. Pass the docs to into the event args.
        VisitorDetailsUpdated?.Invoke(this, new VisitorDetailsUpdatedEventArgs( ... ))
    }
    :
}

class ResidentUpdatedEventArgs : EventArgs
{
    // Properties/fields to hold resident docs
    // Constructor that takes docs
}

class ResidentListener : WhatEverFirebaseBaseClassOrInterfaceNeeded
{
:
    public event EventHandler<ResidentUpdatedEventArgs> ResidentUpdated;

    public void OnEvent(Java.Lang.Object obj, FirebaseFirestoreException error)
    {
        // your code here that extracts resident docs

        // Notify event listeners the C# way, rather than the Java way. Pass the docs to into the event args.
        ResidentUpdated?.Invoke(this, new ResidentUpdatedEventArgs( ... ))
    }
:
}

class YourController
{
    :
    VisitorDetailsListener _visitorDetailsListener = new VisitorDetailsListener();
    ResidentListener _visitorDetailsListener = new ResidentListener();
    :

    public YourController( ... )
    {
        :
        // register for events the C# way
        _visitorDetailsListener.VisitorDetailsUpdated += OnVisitorDetailsUpdated;
        _residentListener.VisitorDetailsUpdated += OnResidentUpdated;
        :
        // register for Firebase events
        visitorDetailsQuery.AddSnapshotListener(_visitorDetailsListener);
        residentQuery.AddSnapshotListener(_residentListener);
        :
    }

    // Handle events the C# way

    void OnVisitorDetailsUpdated(object sender, VisitorDetailsUpdatedEventArgs e)
    {
        // process the visitor details in the event args
    }

    void OnResidentUpdated(object sender, ResidentUpdatedEventArgs e)
    {
        // process the resident in the event args
    }
    :
}

Lines 46-47 above create new instances of C# classes. Lines 50-51 register those classes as listeners for Firebase.

 

[VivekScorp]

Cant thank you enough man, implemented this and it works like a charm

 

[Zeal Ye Lay]

Cant thank you enough man, implemented this and it works like a charm

Is it work?Please share me if you work.

 

[Skydiver]

See post #4 and #6. You don't need to copy and paste someone else's code. You just need to understand and think. You can chose to get a fish, or you can choose to learn how to fish.