Recylerview not automatically loading data from firebase Android Studio

问题

I have tried everything but my data from firebase is not getting loaded automatically when I open the app and I have to click a edittext to load the data.

I have tried

  adapter.Update(data);
  recycler.invalidate();
  notifyDataSetChanged();
  adapter.notifyDataSetChanged();

Please can someone help me out.

EDITED:

I am saving to firebase like this:

    public FirebaseHelper(DatabaseReference db) {
        this.db = db;
    }
    //WRITE IF NOT NULL
    public Boolean save(Spacecraft spacecraft)
    {
        if(spacecraft==null)
        {
            saved=false;
        }else
        {
            try
            {
                db.child("Spacecraft").push().setValue(spacecraft);
                saved=true;
            }catch (DatabaseException e)
            {
                e.printStackTrace();
                saved=false;
            }
        }
        return saved;
    }
    //IMPLEMENT FETCH DATA AND FILL ARRAYLIST
    private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();
        for (DataSnapshot ds : dataSnapshot.getChildren())
        {
            Spacecraft spacecraft=ds.getValue(Spacecraft.class);
            spacecrafts.add(spacecraft);
        }
    }
    //READ THEN RETURN ARRAYLIST
    public ArrayList<Spacecraft> retrieve() {
        db.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                fetchData(dataSnapshot);
            }
            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s){

                fetchData(dataSnapshot);
            }
        });
        return spacecrafts;
    }
}

My viewholder class

public MyViewHolder(View itemView) {
        super(itemView);
        nameTxt= (TextView) itemView.findViewById(R.id.nameTxt);
        propTxt= (TextView) itemView.findViewById(R.id.propellantTxt);
        descTxt= (TextView) itemView.findViewById(R.id.descTxt);
        itemView.setOnClickListener(this);
    }
    public void setItemClickListener(ItemClickListener itemClickListener)
    {
        this.itemClickListener=itemClickListener;
    }
    @Override
    public void onClick(View view) {
        this.itemClickListener.onItemClick(this.getLayoutPosition());
    }

My adapter class

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
    Context c;
    ArrayList<Spacecraft> spacecrafts;
    public MyAdapter(Context c, ArrayList<Spacecraft> spacecrafts) {
        this.c = c;
        this.spacecrafts = spacecrafts;
    }
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v=LayoutInflater.from(c).inflate(R.layout.model,parent,false);
        return new MyViewHolder(v);
    }
    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        final  Spacecraft s=spacecrafts.get(position);
        holder.nameTxt.setText(s.getName());
        holder.propTxt.setText(s.getPropellant());
        holder.descTxt.setText(s.getDescription());
        holder.setItemClickListener(new ItemClickListener() {
            @Override
            public void onItemClick(int pos) {
                //OPEN DETAI ACTIVITY
                openDetailActivity(s.getName(),s.getDescription(),s.getPropellant());
            }
        });
    }
    @Override
    public int getItemCount() {
        return spacecrafts.size();
    }
    //OPEN DETAIL ACTIVITY
    private void openDetailActivity(String...details)
    {
        Intent i=new Intent(c,DetailActivity.class);
        i.putExtra("NAME_KEY",details[0]);
        i.putExtra("DESC_KEY",details[1]);
        i.putExtra("PROP_KEY",details[2]);
        c.startActivity(i);
    }

in my mainactivity in onCreate I am calling the data like this

recycler = (RecyclerView) rootView.findViewById(R.id.recycler);
recycler.setLayoutManager(new LinearLayoutManager(getActivity()));
database = FirebaseDatabase.getInstance().getReference();
spacecraft = new ArrayList<>();
firebasehelper = new FirebaseHelper(database);
adapter = new JAdapter(getActivity(), firebasehelper.retrieve());
recycler.setAdapter(adapter);

回答1:

The problem is with the retrieve method: it's adding a ChildEventListener that executes asynchronously (meaning it doesn't block until the children data are fetched) and then it immediately returns the spacecrafts list which is still not yet filled by the asynchronous listener code.

You should refresh the RecyclerView adapter in the actual code that fetches data, i.e. in the fetchData method, e.g.:

private void fetchData(DataSnapshot dataSnapshot)
{
    spacecrafts.clear();
    for (DataSnapshot ds : dataSnapshot.getChildren())
    {
        Spacecraft spacecraft=ds.getValue(Spacecraft.class);
        spacecrafts.add(spacecraft);
    }
    adapter.spacecrafts = spacecrafts; // update the list in the adapter
    adapter.notifyDataSetChanged(); // refresh
}

In this case, the retrieve method can have a void return type as it is pointless to return the list from it.

回答2:

Use FirebaseRecyclerAdapter for load the data from Firebase.

回答3:

modify the helper constructer to be like this:

 public FirebaseHelper(Context c, DatabaseReference db, ListView lv) {
    this.c = c;
    this.db = db;
    this.lv = lv;
}

then add this to the fetchData method after the for loop:

if (spacecrafts.size() > 0)
    {
        adapter = new CustomAdapter(c, spacecrafts);
        lv.setAdapter(adapter);
        adapter.notifyDataSetChanged();
    }

then in the main activity modify it like this:

    helper = new FirebaseHelper(this, db, lv);
    //ADAPTER
    //adapter = new CustomAdapter(this, helper.retrieve());
    //lv.setAdapter(adapter);
    helper.retrieve();

this should work for you.

回答4:

Check if you are setting up adapter in onCreate() method or not, if you are calling it in onStart() then it will not load data automatically. Set Adapter in onCreate() method.

来源：https://stackoverflow.com/questions/41877876/recylerview-not-automatically-loading-data-from-firebase-android-studio