如何从FIREBASE检索数据到回收站视图

Question

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


    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.menu_recycler);
    recyclerView.setHasFixedSize(true);

    LinearLayoutManager linearLayout = new LinearLayoutManager(this);
    linearLayout.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(linearLayout);

    MenuHomeAdapter menuHomeAdapter = new MenuHomeAdapter(this, createList(7));

    recyclerView.setAdapter(menuHomeAdapter);

    //FireBase
    Firebase.setAndroidContext(this);
    // Get a reference to our posts
    Firebase ref = new Firebase("LINK");

    // Attach an listener to read the data at our posts reference
    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                Menu post = postSnapshot.getValue(Menu.class);
                Toast.makeText(MenuHome.this, post.getSNo() + "-" + post.getDishName(), Toast.LENGTH_LONG).show();
            }
        }

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

如何在回收站视图中显示数据.我尝试了一些方法,但它不合适.吐司工作,但所有其他选项都是错误的.我只想在回收站视图中显示来自firebase的数据.

Answer 1

正如helldawg评论的那样,您需要创建自己的适配器:

• 收听onDataChangeFirebase的来电
• 从Firebase保留数据的内部副本
• 通知RecyclerView数据何时发生变化
• 在需要时创建视图持有者
• 将Firebase数据中的数据绑定到视图

我能想到的最低限度是:

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();
    }
};

要在上下文中查看它,请查看此Github仓库中的Activity34962254(以您的问题编号命名).

你会注意到实现它是非常重要的.虽然这个实现工作,但它是非常次优的.例如:更改/添加/删除单个项目时,将重建整个列表.这是糟糕表现的一个秘诀.

除非您有特定需求,否则最好使用FirebaseRecyclerAdapterFirebaseUI项目.为了全面了解它提供的内容,我建议使用此codelab来构建具有FirebaseUI的聊天应用程序