Question

请帮助我，我试图在./node_modules/.bin/parcel index.html和child("complaints")中获取数据。收集的数据必须存储在List中。儿童名单（“投诉”）和child("complainee") list2。但是，当我显示它时，child("complainee")为null。先感谢您。

list2

这是Personal_RecyclerAdapter，我在其中显示列表和 list2 。列表中的数据已完美显示，但 list2 中的数据未显示/ null。

        database = FirebaseDatabase.getInstance();
        myRef = database.getReference("complaints");

        list = new ArrayList<Blog>();
        list2 = new ArrayList<Complainee>();

        myRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                try{

                    for(DataSnapshot dataSnapshot1 :dataSnapshot.getChildren()){

                        final Blog value = dataSnapshot1.getValue(Blog.class);
                        Boolean Posted = value.getPosted();
                        String complaint_type = value.getComplaintType();

                        if(complaint_type.equals("Personal Complaint")) {

                            final int ComplaintNo = value.getComplaintNo();
                            String Description = value.getDescription();
                            String Date = value.getDate();
                            String MediaURL = value.getMediaURL();
                            String Time = value.getTime();
                            String Address = value.getAddress();

                            final Blog fire = new Blog();
                            fire.setComplaintNo(ComplaintNo);
                            fire.setDescription(Description);
                            fire.setDate(Date);
                            fire.setMediaURL(MediaURL);
                            fire.setTime(Time);
                            fire.setAddress(Address);
                            fire.setComplainee_Name(value.getComplainee_Name());



                           // Read from the database for COMPLAINEE
                           FirebaseDatabase database2 = FirebaseDatabase.getInstance();
                            DatabaseReference myRef2 = database2.getReference("complainee").child(String.valueOf(ComplaintNo));

                            myRef2.addValueEventListener(new ValueEventListener() {
                                @Override
                                public void onDataChange(DataSnapshot dataSnap) {

                                    Complainee cm = dataSnap.getValue(Complainee.class);

                                    String n = cm.getName();

                                    final Complainee fire2 = new Complainee();
                                    fire2.setName(n);
                                    fire2.setAddress("Address");
                                    list2.add(fire2);


                                }


                                @Override
                                public void onCancelled(DatabaseError databaseError) {

                                }
                            });

                            list.add(fire);
                        }

                    }

                    Personal_RecyclerAdapter recyclerAdapter = new Personal_RecyclerAdapter(list,list2, getContext());
                    RecyclerView.LayoutManager recyce = new GridLayoutManager(getContext(),1);
                    recyclerView.setLayoutManager(recyce);
                    recyclerView.setItemAnimator( new DefaultItemAnimator());
                    recyclerView.setAdapter(recyclerAdapter);


                }catch (Exception e){

                    Toast.makeText(getContext(), "::ERROR   " + e.toString(), Toast.LENGTH_LONG).show();
                }

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

Answer 1

您正在初始化儿童和投诉的数据库参考＆＃34;写myRef = database.getReference("complaints"); 这就是为什么在＃34;抱怨＆＃34;儿童。改变你的参考 -

myRef = database.getReference();

然后使用

获取值

myRef.child("complainee").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ............

和另一个

myRef.child("complaints").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ............

希望你的问题能够得到解决。

Answer 2

这是由于firebase侦听器的异步性质，您还没有通知适配器更改。在您的情况下，您要将项目添加到列表list.add(fire)，然后您已定义了回收站视图。但是您还没有等待将list2的数据添加到list2.add(fire2)中。

以下是您的代码的外观：

    database = FirebaseDatabase.getInstance();
    myRef = database.getReference("complaints");
    Personal_RecyclerAdapter recyclerAdapter = new Personal_RecyclerAdapter(list,list2, getContext());
    RecyclerView.LayoutManager recyce = new GridLayoutManager(getContext(),1);
    recyclerView.setLayoutManager(recyce);
    recyclerView.setItemAnimator( new DefaultItemAnimator());
    recyclerView.setAdapter(recyclerAdapter);
    list = new ArrayList<Blog>();
    list2 = new ArrayList<Complainee>();

    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            try{

                for(DataSnapshot dataSnapshot1 :dataSnapshot.getChildren()){

                    final Blog value = dataSnapshot1.getValue(Blog.class);
                    Boolean Posted = value.getPosted();
                    String complaint_type = value.getComplaintType();

                    if(complaint_type.equals("Personal Complaint")) {

                        final int ComplaintNo = value.getComplaintNo();
                        String Description = value.getDescription();
                        String Date = value.getDate();
                        String MediaURL = value.getMediaURL();
                        String Time = value.getTime();
                        String Address = value.getAddress();

                        final Blog fire = new Blog();
                        fire.setComplaintNo(ComplaintNo);
                        fire.setDescription(Description);
                        fire.setDate(Date);
                        fire.setMediaURL(MediaURL);
                        fire.setTime(Time);
                        fire.setAddress(Address);
                        fire.setComplainee_Name(value.getComplainee_Name());



                       // Read from the database for COMPLAINEE
                        DatabaseReference myRef2 = database.getReference("complainee").child(String.valueOf(ComplaintNo));

                        myRef2.addValueEventListener(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnap) {

                                Complainee cm = dataSnap.getValue(Complainee.class);

                                String n = cm.getName();

                                final Complainee fire2 = new Complainee();
                                fire2.setName(n);
                                fire2.setAddress("Address");
                                list2.add(fire2);
                                // Notify to your recyclerview that for the new data
                                recyclerAdapter.notifyDataSetChanged();

                            }


                            @Override
                            public void onCancelled(DatabaseError databaseError) {

                            }
                        });

                        list.add(fire);
                        // Notify to your recyclerview that for the new data
                        recyclerAdapter.notifyDataSetChanged();

                    }

                }




            }catch (Exception e){

                Toast.makeText(getContext(), "::ERROR   " + e.toString(), Toast.LENGTH_LONG).show();
            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

一旦获得数据，您必须通知recyclerview适配器数据集中存在一些更改。

希望它有所帮助！

Answer 3

您只需要像这样查询。

     FirebaseDatabase mDatabase;

     DatabaseReference mDatabaseReference;

     List<Complainee> complaineeList=new ArrayList();



        mDatabase = FirebaseDatabase.getInstance();
        mDatabaseReference = mDatabase.getReference();

         mdatabaseRef.child("complainee").addValueEventListener(new ValueEventListener() {
      @Override     
      public void onDataChange(DataSnapshot dataSnapshot) {
         for (DataSnapshot childSnapshot: dataSnapshot.getChildren()){

            if(complaineeList.size>0){
             complaineeList.clear();
             }

     Complainee complainee  =  childSnapshot.getValue(Complainee.class );

       complaineeList.add(complainee);




             }

     Adapter recyclerAdapter = new Adapter(complaineeList, getContext());

        }

如何使用Firebase从不同的孩子中添加列表中的值？

3 个答案: