試圖從另一個 firebase 數據庫中檢索數據

Question

我正在嘗試從另一個 firebase 數據庫中檢索數據，但我什么也沒顯示。 我沒有收到任何錯誤，我的應用程序沒有崩潰，這是一件好事，但它沒有顯示任何數據並且數據庫中有數據。

有人可以幫我解決這個問題嗎？

recyclerView.setLayoutManager(layoutManager);
myUploads = new ArrayList<Model_Information>();
aAdapter = new Adapter1(getContext(), myUploads);
recyclerView.setAdapter(aAdapter);
aAdapter.notifyDataSetChanged();

DatabaseReference databaseReference = FirebaseDatabase.getInstance("https://boot0-43081.firebaseio.com/").getReference("Posts");

if (InternetConnection.checkConnection(getContext())) {
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists()){
                for (DataSnapshot postsnapshot : dataSnapshot.getChildren()) {
                    Model_Information upload=postsnapshot.getValue(Model_Information.class);

                    myUploads.add(upload);
           
                    recyclerView.invalidate();
                }
                linearLayoutWithoutItems.setVisibility(View.GONE);
                recyclerView.setVisibility(View.VISIBLE);

             aAdapter.notifyDataSetChanged();

            }else{
                linearLayoutWithoutItems.setVisibility(View.VISIBLE);
                recyclerView.setVisibility(View.GONE);

            }

Json

{
  "Posts" : {
    "37trzrENv0WGEgHWTPvKZ08wWcY2" : {
      "-MT1gIzSVIG4cF_ipquI" : {
        "created" : "2-09-2021",
        "headline" : "Danny Dinner",
        "id" : "-MT1gIzSVIG4cF_ipquI",
        "mImageUrl" : "https://firebasestorage.googleapis.com/v0/b/boot0-43081.appspot.com/o/37trzrENv0WGEgHWTPvKZ08wWcY2%2F1612805391640.jpg?alt=media&token=9e819b43-507d-4c07-91cb-c006e16a8def",
        "main_id" : "-MT1gIzSVIG4cF_ipquI",
        "time" : "1:29 AM",
        "timestamp" : 1612805393601,
        "views" : 0,
        "websiteurl" : "www.danny.com"
      }
    }
  },

Answer 1

從外觀上看，您的Posts節點有一個鍵，其中包含用戶的 UID，然后在下面有該用戶的帖子列表。

由於您的代碼讀取整個Posts節點，因此它需要在此處處理兩個嵌套級別：用戶和帖子。 所以你需要兩個嵌套循環：

DatabaseReference databaseReference = FirebaseDatabase.getInstance("https://boot0-43081.firebaseio.com/").getReference("Posts");

if (InternetConnection.checkConnection(getContext())) {
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists()){
                for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
                    for (DataSnapshot postsnapshot : userSnapshot.getChildren()) {
                        Model_Information upload=postsnapshot.getValue(Model_Information.class);

                        myUploads.add(upload);           
                        recyclerView.invalidate();
                    }
                }
                linearLayoutWithoutItems.setVisibility(View.GONE);
                recyclerView.setVisibility(View.VISIBLE);

             aAdapter.notifyDataSetChanged();
            }else{
                linearLayoutWithoutItems.setVisibility(View.VISIBLE);
                recyclerView.setVisibility(View.GONE);
            }

或者，如果您只想閱讀當前用戶的帖子，那就是：

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference databaseReference = FirebaseDatabase.getInstance("https://boot0-43081.firebaseio.com/")
    .getReference("Posts").child(uid);

然后你可以保持onDataChange 。