How to subscribe Firebase realtime DB event

FiresharpEventHandling.cs

        //client1 = new FireSharp.FirebaseClient(new FirebaseConfig(...));
        client1.OnAsync(StringPath, Added, Changed, Removed);

        private void Removed(object sender, ValueRemovedEventArgs args, object context)
        {
            Log(args.Path + " removed");
        }

        private void Changed(object sender, ValueChangedEventArgs args, object context)
        {
            Log(args.Path + " changed from " + args.OldData + " to " + args.Data);
        }

        private void Added(object sender, ValueAddedEventArgs args, object context)
        {
            Log(args.Path + " added");
        }
        
        private void Log(string info)
        {
            InfoBox.Text += Environment.NewLine + info; //InfoBox is a ListBox UI control
        }