Remove object from list on child removed android

Question

I have an arrayList of objects of a class. This class contains data received from Firebase.

but I want to remove an object from the list when a child is removed in firebase, but two objects don't match because the snapshot creates a new object of the class containing the same data. Here is the code of what I have implemented :

posts = new ArrayList<>();

        childEventListener= new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                posts.add(dataSnapshot.getValue(GalleryPostModel.class));
                unapprovedAdapter.notifyDataSetChanged();
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
                posts.remove(dataSnapshot.getValue(GalleryPostModel.class));
                unapprovedAdapter.notifyDataSetChanged();
            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        };

        UnApprovedDbRef.addChildEventListener(childEventListener);

So how do I approach this problem ? what can I do to remove it from the list. I could do a linear search in the list, but when the list becomes huge, this task will become very time consuming. (Cannot use .removeIf because it requires a minimum api level 24 but my app's min api is 22)

Answer 1

To be able to remove the item you must keep its key, in addition to keeping the value.

So you create an addition list for the keys:

keys = new ArrayList<String>();

And then in onChildAdded , add the key of the snapshot to this list:

public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
    posts.add(dataSnapshot.getValue(GalleryPostModel.class));
    keys.add(dataSnapshot.getKey());
    unapprovedAdapter.notifyDataSetChanged();
}

Now you can look up the key in onChildRemoved , which is a lot faster than looking up the post/value:

public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
    int index = keys.indexOf(dataSnapshot.getKey());
    posts.remove(index);
    keys.remove(index);
    unapprovedAdapter.notifyDataSetChanged();
}