In an effort to reduce data transfer (since it's costing us a lot of money), we're in the process of updating our Firebase Realtime Database value listener to use child listeners. Since most of the fields don't change, and the ones that change most frequently we only care about in certain app states, using only child added and child removed listeners seems to fit the bill.

Adding listeners for just child_added and child_removed appears to work perfectly on web. And iOS seems to be set up that way as well, though I admittedly haven't tested there yet. Android, however, appears to require that we add one massive listener that will listen for child moved and child changed too.

Listening for these, to my understanding, mostly defeats the purpose of using the child listeners over the value listener. Since any time any of the child's data changes (most of which we don't care about most of the time), it will send the entire child's snapshot again. We're trying to avoid data transfer by only listening for added/removed and circumstantially specific child properties, but this requires we basically listen to all of it at all times? Is there another way to implement this, to get what I'm hoping for?

To summarize our object, we have:

parent
--child A
----child A property 1
----child A property 2
--child B
----child B property 1
----child B property 2

etc. And we want to know when a child is added or removed, but most of the time we don't care about keeping the child's properties updated and would prefer to avoid re-transferring that data. How is that accomplished on Android (using Java, specifically)? Thanks!

CodePudding user response：

There is no difference between the data transferred for a ValueEventListener vs a ChildEventListener when they are used on the same query/path in the database.

If you only want to know when a child is added/remove, but not about their contents, consider adding an additional top-level branch to your tree, where you keep just the key of the child node and then true as its value.