How do I limit the items FirebaseRecyclerAdapter pulls from the server?

Question

I'm using the tutorial project and can't understand how to limit the number of items pulled.

Answer 1

You can initialize your FirebaseRecyclerAdapter with either a DatabaseReference or with a Query. When you use a DatabaseReference the adapter will show all data at that location. E.g. (from the FirebaseUI docs):

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
DatabaseReference chatRef = ref.child("chat_messages");

mAdapter = new FirebaseListAdapter<Chat>(this, 
                                         Chat.class, 
                                         android.R.layout.two_line_list_item, 
                                         chatRef) {
    @Override
    protected void populateView(View view, Chat chatMessage, int position) {
        ((TextView)view.findViewById(android.R.id.text1)).setText(chatMessage.getName());
        ((TextView)view.findViewById(android.R.id.text2)).setText(chatMessage.getText());

    }
};
messagesView.setAdapter(mAdapter);

To only show the last 5 chat messages, you'd create a query and pass that into the adapter:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
DatabaseReference chatRef = ref.child("chat_messages");
Query recentMessages = chatRef.limitToLast(5);

mAdapter = new FirebaseListAdapter<Chat>(this, 
                                         Chat.class, 
                                         android.R.layout.two_line_list_item, 
                                         recentMessages) {
    @Override
    protected void populateView(View view, Chat chatMessage, int position) {
        ((TextView)view.findViewById(android.R.id.text1)).setText(chatMessage.getName());
        ((TextView)view.findViewById(android.R.id.text2)).setText(chatMessage.getText());

    }
};
messagesView.setAdapter(mAdapter);

There's a lot more you can do with Firebase Database queries. Read the documentation on sorting and filtering data for more.