Database > firebaseArray uses private member functions

[kmcnellis]

• FirebaseUI version: 2.3.0

Its very hard to subclass the firebaseArray class (for the database recyclerview), due to the member functions being private, not protected (esp. getIndexForKey). This is needed to implement custom functionality.

[Kurt29]

There was just a Thread about that.
#898

[samtstern]

@kmcnellis can you tell us more about the features you're trying to implement on top of FirebaseArray? We are working (as @Eragon29 pointed out) to get some of this visibility stuff ironed out for 3.0.

[SUPERCILEX]

@kmcnellis Yeah, I'm actually leaning towards completely preventing inheritance. @samtstern convinced me to not make the Firebase arrays final for testing and mockability's sake, but all the methods are private and final where possible. I can't think of any scenario where using a wrapper couldn't do a better job.

Since you're asking about getIndexForKey, I'm guessing you're looking for custom sorting? That could easily be achieved with a wrapper object that extends ObservableSnapshotArray.

[bagintz]

@SUPERCILEX Can you explain a little more how one would implement a wrapper object that extends ObservableSnapshotArray for custom sorting? I am now running into this to :-/

[SUPERCILEX]

@bagintz There are two options:

1. You can use our method of sorting with your own custom list of snapshots by simply copying the getIndexForKey method.
2. Or, since you're pulling data from different sources that's probably going to be difficult, so instead, you can use DiffUtil to asyncronously figure out the proper order of your items and then call the related notify metods once DiffUtil returns a set of operations to transform your existing list into your updated properly sorted list of snapshots.

But like I said in the other thread, the RTDB really isn't designed for this kind of stuff. Instead, you should duplicate your data so you can get everything in the right order all in one pretty query.

[bagintz]

@SUPERCILEX
Ok, I was trying to use a custom comparator on the ObservableSnapshotArray and that was not working. I would much prefer #2, but am a little unclear how it would work. I updated the search index to use a single key to find items by user and status

query_key = [uid]_[status]

Which let's me get the data with one query (which is how I "fixed" the issue I was having in the other thread). But now I want to get that resultant list of items sorted by a date field that is in there. How am I able to use the "filter" with my new query_key above and then add something that helps me sort by date.

Thanks for the tips!

[SUPERCILEX]

For that, you can use setValue(..., priority) where the priority is a long timestamp and then use orderByPriority() on the Query. Or, I think orderBy("timestamp") would also work.

[bagintz]

@SUPERCILEX ok, I will take a look, I thought I could only have 1 orderby, since I am using the orderByChild to query for my [query_key] ??? Thanks again

[SUPERCILEX]

@bagintz Oh shoot, I didn't know you were using orderby for the query. Does equalTo not work? Otherwise, you'll have to use client side sorting as mentioned with DiffUtil.

[bagintz]

ref.orderByChild('query_key').equalTo('[uid]_[status') works great to get me my 4 values, but they each have a startDate (and weren't entered into Firebase in the correct order).

So I think client side is the way to go. I haven't used DiffUtil, I will give it a shot and come back if I have any questions :)

[bagintz]

@SUPERCILEX Ok, I think I can see how I can get there with DiffUtil, the problem is that my ArrayList that I am using to populate the Adapter is showing a size of 0 even though it shows the correct 4 cards in my view:

Query myRef = loansRef.orderByChild("query_key").equalTo(queryString);
ObservableSnapshotArray<Loan> myArray = new FirebaseArray<>(myRef, POJO.class);
adapter = new Adapter(myArray, R.layout.item, Adapter.ViewHolder.class);

Works fine, but if I try to get the size of myArray it shows 0, which doesn't let me do any sorting before sending the updated array to DiffUtil. Am I doing my wrapper object of snapshots wrong?

[bagintz]

@SUPERCILEX OK!! I got it working with diffutil. 2 quick questions:

1. Would it be helpful to do some sort of small writeup on what I did for future folks, and where should that go?
2. The only place I can find to do the initial diffutil to sort is onDatachanged, but that seems very inefficient, not to mention a little "jarring" to have the list show up and sort visually in front of you. Is there any other place in the FirebaseRecyclerAdapter that I can trigger the initial sort AFTER the mSnapshots has been populated, but before the initial view is created?
3. [edited] Also, it seems to not seem to work "out of the box" with custom sorting when data is changed directly in Firebase. Do I need to do something special to make this work?

Thank you so much

[bagintz]

@SUPERCILEX I think I am going to give up for now. It seems the DiffUtil won't work since the FirebaseRecyclerAdapter's snapshots are immutable so the clear and addAll methods won't work. This causes the list to "look" correct, but it does not update the true location for the Firebase listeners :(

Let me know if you have any other ideas.

final SnapshotDiffCallback diffCallback = new SnapshotDiffCallback(this.mSnapshots, sortedSnapshots);
final DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(diffCallback);

// clear snapshots and add
this.mSnapshots.clear();
this.mSnapshots.addAll(sortedSnapshots);

diffResult.dispatchUpdatesTo(this); // calls adapter's notify methods after diff is computed

[SUPERCILEX]

@bagintz You're not quite understanding what I mean by "wrapper object". I going to do a bit of whiteboard coding here so please bear with me:

class MySortedSnapshots extends ObservableSnapshotArray<MyModel> {
    List<DataSnapshot> mSortedSnapshots = new ArrayList(); // Hold you sorted snapshots and return them in List#get(int)

    // Get your data with other FirebaseArrays, then calculate a diff and update the wrapper object
    void onNewUpdateRecieved() {
        FirebaseArray.addChangeEventListener ...

        Tasks.call(myAsyncExecutor, () -> DiffUtil.calculateDiff(...); ).addOnSuccessListener(result -> {
            result.dispatchUpdatesTo(new ListUpdateCallback() {
                @Override
                public void onInserted(int position, int count) {
                    notifyOnChildChanged(ChangeEventType.ADDED, ...);
                }
    
                @Override
                public void onRemoved(int position, int count) {
                    // ...
                }
    
                @Override
                public void onMoved(int fromPosition, int toPosition) {
                    // ...
                }
    
                @Override
                public void onChanged(int position, int count, Object payload) {
                    // ...
                }
            });
        }
    }
}

Do you see what I'm doing here? You're basically implementing your own FirebaseArray but using composition with other FirebaseArrays. You can have a look at the more complex FirebaseIndexArray to get a general idea of what you should be doing. Hope this helps! 😄