如何从 Firebase 获取数据到 Recyclerview 中的片段？答案

【问题标题】：How to Fetch data form firebase to fragments in Recyclerview?如何从 Firebase 获取数据到 Recyclerview 中的片段？
【发布时间】：2021-10-06 11:50:57
【问题描述】：

Java
这是我的应用程序片段的代码，当我运行它时，我的应用程序在我启动应用程序时立即崩溃，得到客户主页片段它崩溃，在 logcat 中它显示 CustomerHomefragemnt 中有错误所以这是我无法使用的代码解决它如果有人可以提供帮助，请回答。这是我的片段代码`

    public class CustomerHomeFragment extends Fragment implements 
    SwipeRefreshLayout.OnRefreshListener {

    RecyclerView recyclerView;
    private List<UpdateDishModel> updateDishModelList;
    private CustomerHomeAdapter adapter;
    String State, City, Sub;
    DatabaseReference dataaa, databaseReference;
    SwipeRefreshLayout swipeRefreshLayout;
    SearchView searchView;


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, 
    @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_customerhome, null);
        setHasOptionsMenu(true);

        recyclerView = v.findViewById(R.id.recycle_menu);
        recyclerView.setHasFixedSize(true);
        Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.move);
        recyclerView.startAnimation(animation);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
        updateDishModelList = new ArrayList<>();
        swipeRefreshLayout = (SwipeRefreshLayout) v.findViewById(R.id.swipelayout);
        swipeRefreshLayout.setOnRefreshListener(this);
        swipeRefreshLayout.setColorSchemeResources(R.color.colorPrimaryDark, R.color.green);


        swipeRefreshLayout.post(new Runnable() {
            @Override
            public void run() {
                swipeRefreshLayout.setRefreshing(true);
                String userid = FirebaseAuth.getInstance().getCurrentUser().getUid();
                dataaa = FirebaseDatabase.getInstance()
                           .getReference("Customer").child(userid);
                dataaa.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        Customer cust = dataSnapshot.getValue(Customer.class);
                        State = cust.getState();
                        City = cust.getCity();
                        Sub = cust.getSuburban();
                        customermenu();
                    }


                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {

                    }
                });
            }
        });

        return v;
    }


    @Override
    public void onRefresh() {
        customermenu();
    }

    private void customermenu() {

        swipeRefreshLayout.setRefreshing(true);

        DatabaseReference databaseReference = 
    FirebaseDatabase.getInstance().getReference("FoodSupplyDetails")
          .child(State).child(City).child(Sub);
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                updateDishModelList.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    for (DataSnapshot snapshot1 : snapshot.getChildren()) {
                        UpdateDishModel updateDishModel = 
    snapshot1.getValue(UpdateDishModel.class);
                        updateDishModelList.add(updateDishModel);
                    }
                }
                adapter = new CustomerHomeAdapter(getContext(), updateDishModelList);
                recyclerView.setAdapter(adapter);
                swipeRefreshLayout.setRefreshing(false);

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

                swipeRefreshLayout.setRefreshing(false);
            }
        });
        searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String query) {
                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                search(newText);
                return true;
            }
        });

    }
    


    private void search(final String searchtext) {

        ArrayList<UpdateDishModel> mylist = new ArrayList<>();
        for (UpdateDishModel object : updateDishModelList) {
            if (object.getDishes().toLowerCase().contains(searchtext.toLowerCase())) {
                mylist.add(object);
            }
        }
        adapter = new CustomerHomeAdapter(getContext(), mylist);
        recyclerView.setAdapter(adapter);

    }


    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.search, menu);
        MenuItem menuItem = menu.findItem(R.id.Searchdish);
        searchView = (SearchView) menuItem.getActionView();
        searchView.setQueryHint("Search Dish");


      }
    }
```


`here is my Homeadapter code`



    public class CustomerHomeAdapter extends  
             RecyclerView.Adapter<CustomerHomeAdapter.ViewHolder>
    {


    private Context mcontext;
    private List<UpdateDishModel>updateDishModellist;
    DatabaseReference databaseReference;

    public CustomerHomeAdapter(Context context,List<UpdateDishModel>updateDishModellist)
    {
        this.updateDishModellist=updateDishModellist;
        this.mcontext=context;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view= 
            LayoutInflater.from(mcontext)
                 .inflate(R.layout.customer_menudish,parent,false);
        return new CustomerHomeAdapter.ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull final ViewHolder holder, int position) {

        final UpdateDishModel updateDishModel=updateDishModellist.get(position);
        Glide.with(mcontext).load(updateDishModel.getImageURL()).into(holder.imageView);
        holder.Dishname.setText(updateDishModel.getDishes());
        updateDishModel.getRandomUID();
        updateDishModel.getChefId();
        holder.price.setText("Price: ₹ " + updateDishModel.getPrice());
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent intent=new Intent(mcontext,OrderDish.class);
                intent.putExtra("FoodMenu",updateDishModel.getRandomUID());
                intent.putExtra("ChefId",updateDishModel.getChefId());


                mcontext.startActivity(intent);
            }
        });
    }

    @Override
    public int getItemCount() {
        return updateDishModellist.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        ImageView imageView;
        TextView Dishname,price;
        ElegantNumberButton additem;
        public ViewHolder(@NonNull View itemView) {
            super(itemView);

            imageView=itemView.findViewById(R.id.menu_image);
            Dishname=itemView.findViewById(R.id.dishname);
            price=itemView.findViewById(R.id.dishprice);
            additem=itemView.findViewById(R.id.number_btn);


        }
    }
   }

我认为此代码中存在错误，因为我无法解决问题，请帮助我解决此问题

private void customermenu() {
    
            swipeRefreshLayout.setRefreshing(true);
    
            DatabaseReference databaseReference = 
        FirebaseDatabase.getInstance().getReference("FoodSupplyDetails")
              .child(State).child(City).child(Sub);
            databaseReference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    updateDishModelList.clear();
                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        for (DataSnapshot snapshot1 : snapshot.getChildren()) {
                            UpdateDishModel updateDishModel = 
        snapshot1.getValue(UpdateDishModel.class);
                            updateDishModelList.add(updateDishModel);
                        }
                    }
                    adapter = new CustomerHomeAdapter(getContext(), updateDishModelList);
                    recyclerView.setAdapter(adapter);
                    swipeRefreshLayout.setRefreshing(false);
    
                }
    
                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
    
                    swipeRefreshLayout.setRefreshing(false);
                }
            });

enter image description here

【问题讨论】：

你遇到了什么错误？
当我移动到 customerhomefragment 活动时，我的应用程序崩溃了。我认为在从 firebase 获取数据时存在一些问题，我附上了图片链接，该链接定义了错误在 customerhomefragment 的私有 void 方法中。如果可以请帮助我，这会很棒

标签： java android firebase-realtime-database firebase-authentication

【解决方案1】：

从您的代码来看，您的问题似乎在下面一行：

FirebaseDatabase.getInstance().getReference("FoodSupplyDetails")
              .child(State).child(City).child(Sub);

错误告诉您不能为“.child()”传递 null。所以它告诉你 State、City 和 Sub 的值为空。您可以通过转到 Firebase 的控制台数据库并查看具有 firebase id 的相应“客户”的数据结构来确认这一点。

请检查您的 Firebase 数据库并确保客户数据存在。

【讨论】：

我附上了客户和 fooddetails 根的屏幕截图，来自 firebase 库，您可以参考存在数据但未获取数据，请帮助我
Sub 的值是多少？我在客户中没有看到它。没有郊区节目。通过将 Sub 和 value 密钥对添加到您的 Customer 中进行快速测试，然后重试。

【解决方案2】：

在运行查询之前，您应该确保值不为空。

if (State != null && City != null && Sub != null) {
  // Run your query here
} else {
  Log.d("TAG", "Data provided is null")
}

当您获取客户信息时，请尝试记录该信息并检查其中哪些为空：

String State, City, Sub;
//...

State = cust.getState();
City = cust.getCity();
Sub = cust.getSuburban();

Log.d("TAG", State);
Log.d("TAG", City);
Log.d("TAG", Sub);

// call customermenu now
customermenu();

【讨论】：

嘿，它提供的显示数据为空，那么我如何从 firebase 获取它，我的代码有什么问题？？
@VaibhavKale 它在哪里记录 null？从数据库或内部客户菜单功能中获取后？
我的活动中没有获取任何内容，但应用程序只是停止崩溃，所以我应该如何获取它？我是这个领域的初学者，请帮助我。
我加入了你的不和谐。我们应该如何以及在哪个房间谈论？？

【解决方案3】：

错误告诉您不能为“.child()”传递 null。所以它告诉你数据的值（存储在 firebase 数据库中）为空。您可以通过访问 Firebase 的控制台数据库并查看与 firebase id 对应的数据结构来确认这一点。

【讨论】：