how to retrieve data to a recycler view from FIREBASE

Question

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_menu_home);


    Toolbar         


        

Answer 1

As helldawg commented, you'll need to create your own adapter that:

• listens to onDataChange calls from Firebase
• keeps an internal copy of the data from Firebase
• informs the RecyclerView when the data changes
• creates view holders when those are needed
• binds data from the Firebase data to the view

The minimum I could come up with quickly is:

public static class MenuHomeAdapter extends RecyclerView.Adapter<MenuViewHolder> {
    ArrayList<Menu> items = new ArrayList<>();

    public MenuHomeAdapter(Firebase ref) {
        ref.addValueEventListener(new ValueEventListener() {
            public void onDataChange(DataSnapshot snapshot) {
                items.clear();
                for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                    Menu menu = postSnapshot.getValue(Menu.class);
                    items.add(menu);
                }
                notifyDataSetChanged();
            }

            public void onCancelled(FirebaseError firebaseError) {
                System.out.println("The read failed: " + firebaseError.getMessage());
            }
        });
    }

    public MenuViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
        return new MenuViewHolder(view);
    }

    public void onBindViewHolder(MenuViewHolder holder, int position) {
        Menu item = items.get(position);
        holder.getTitleView().setText(item.getTitle());
    }

    public int getItemCount() {
        return items.size();
    }
};

To see it in context, look at Activity34962254 (named after the number of your question) on this Github repo.

You'll note that implementing this is fairly non-trivial. And while this implementation works, it is pretty sub-optimal. For example: when a single item is changed/added/deleted, the entire list is rebuilt. That's a recipe for bad performance.

Unless you have specific needs, you're probably better off using the FirebaseRecyclerAdapter from the FirebaseUI project. To get a full walkthrough of what that offers, I recommend this codelab for building a chat app with FirebaseUI

Answer 2

There is a pretty good tutorial here

https://github.com/firebase/FirebaseUI-Android#using-firebaseui-to-populate-a-recyclerview

That will give you what you need, and also FirebaseUI gives you a lot to play with.

Now if you want to include databinding as well:

Custom ViewHolder

public class YourViewHolder extends RecyclerView.ViewHolder {

    public YourItemBinding binding;

    public YourViewHolder(View itemView) {
        super(itemView);

        binding = DataBindingUtil.bind(itemView);
    }

    public YourItemBinding getBinding() {
        return binding;
    }
}

FirebaseRecyclerAdapter

mAdapter = new FirebaseRecyclerAdapter <YourFirebaseItem, YourViewHolder> (YourFirebaseItem.class, android.R.layout.two_line_list_item, YourViewHolder.class, mRef) {

    @Override
    public void populateViewHolder(YourViewHolder viewHolder, YourFirebaseItem item, int position) {

        YourItemBinding binding = viewHolder.getBinding();

        binding.setItem(item);

    }
};

recycler.setAdapter(mAdapter);

Answer 3

Why not simply using the FirebaseRecyclerAdapter ?

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

RecyclerView messages = (RecyclerView) findViewById(R.id.messages);
messages.setLayoutManager(new LinearLayoutManager(this));

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();

mAdapter = new FirebaseRecyclerAdapter<Chat, ChatHolder>(
        Chat.class,
        R.layout.message,
        ChatHolder.class,
        ref) {
    @Override
    public void populateViewHolder(ChatHolder holder, Chat chat, int position) {
        holder.setName(chat.getName());
        holder.setMessage(chat.getMessage());
    }
};

messages.setAdapter(mAdapter);
}