空 Recyclerview firebase [重复]

Question

我的RecyclerView 有问题。总之，我把一个 RecyclerView 连接到我的数据库。然后当我开始活动时，列表是空的。

public static class Chartviewholder extends RecyclerView.ViewHolder{
    View mView;
    public Chartviewholder(View itemView){
        super(itemView);
        mView = itemView;
    }
    public void setTitleProduct(String title){
        TextView post_title = (TextView)mView.findViewById(R.id.tvProductName);
        post_title.setText(title);
    }
    public void setImgProduct(String desc){
        ImageView post_desc = (ImageView) mView.findViewById(R.id.productIV);
        Picasso.get().load(desc).into(post_desc);
    }
    public void setPriceProduct( String price){
        TextView post_image = (TextView) mView.findViewById(R.id.tvProductPrice);
        post_image.setText(price);
    }
    public void setDescProduct(String desc){
        TextView post_desc=(TextView) mView.findViewById(R.id.tvProductDesc);
        post_desc.setText(desc);
    }



}

这是我在主类中的代码，恰好在方法 OnCreate 中

dbchart = FirebaseDatabase.getInstance().getReference().child("product");
    dbchart.keepSynced(true);

    chartrv = (RecyclerView) findViewById(R.id.chartrv);

    DatabaseReference personsRef2 = FirebaseDatabase.getInstance().getReference().child("product");
    Query personsQuery2 = personsRef2.orderByKey();

    chartrv.hasFixedSize();
    chartrv.setLayoutManager(new LinearLayoutManager(this));

    FirebaseRecyclerOptions personsOptions2 = new FirebaseRecyclerOptions.Builder<Product>().setQuery(personsQuery2, Product.class).build();

    chartAdapter=new FirebaseRecyclerAdapter<Product, Chartviewholder>(personsOptions2) {
        @Override
        protected void onBindViewHolder(@NonNull final Chartviewholder holder, int position, @NonNull final Product model) {
            holder.setTitleProduct(model.product_name.toString());
            holder.setImgProduct(model.product_image.toString());
            holder.setDescProduct(model.Product_desc.toString());
            holder.setPriceProduct(Integer.toString(model.product_price)+" DH");
            Button cart=findViewById(R.id.button15);
            cart.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    addorder(model);
                }
            });

        }


        @NonNull
        @Override
        public Chartviewholder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.products_list_item2, parent, false);
            return new Chartviewholder(view);
        }
    };
    chartrv.setAdapter(chartAdapter);

Answer 1

您需要使用startListening() 开始监听数据。来自文档：

FirebaseRecyclerAdapter 使用事件侦听器来监控 Firebase 查询的更改。要开始侦听数据，请调用startListening() 方法。您可能想在 onStart() 方法中调用它。在调用 startListening() 之前，请确保您已完成读取数据所需的任何身份验证，否则您的查询将失败。

@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();
}

更多信息在这里：

https://github.com/firebase/FirebaseUI-Android/blob/master/database/README.md#using-firebaseui-to-populate-a-recyclerview