如何从Firebase数据库读取数据到列表

Question

Before going into the issue here is the database structure in question

So, I am trying to read all available data under the child KkOz7Zg9iNqms1vZJA6 . The issue I am facing right now is in reading the Values inside the child -KkOz7Zg9iNqms1vZJA6 / articleTags . I tried using the following code

List<ModelContentTag> TagList_Chosen;

FirebaseDatabase.getInstance().getReference()
       .child("articles")
       .child("content")
       .child("ta")
       .child("all")
       .child("KkOz7Zg9iNqms1vZJA6")
       .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                TagList_Chosen = new ArrayList<>();

                int b = 0;
                for (DataSnapshot tagNameSnapshot : dataSnapshot.getChildren()) {
                    String TagName_Chosen = tagNameSnapshot
                            .child("articleTags")
                            .child(String.valueOf(b))
                            .getValue(String.class);
                    TagList_Chosen.add(new ModelContentTag(TagName_Chosen));
                    Toast.makeText(getActivity(), TagName_Chosen, Toast.LENGTH_SHORT).show();
                    b++;
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {/*Do Nothing*/}
       });

Since the Key values are simply "0", "1", "2", "3" and so on, I tried using an Integer b which increments during every iteration in For loop.

The List tagList_Chosen and even the String TagName_Chosen always returns empty. Can someone point me to the problem in my code? Where am I going wrong?

Thanks

Answer 1

Try like this way,

Inside OnDataChange use iterator,

  Iterator<DataSnapshot> dataSnapshotsChat = dataSnapshot.child("articleTags").getChildren().iterator();

  while (dataSnapshotsChat.hasNext()) {
                DataSnapshot dataSnapshotChild = dataSnapshotsChat.next();
                String TagName_Chosen = dataSnapshotChild.getValue(String.class); // check here whether you are getting the TagName_Chosen                   
     }

Answer 2

Please use this code:

FirebaseDatabase.getInstance().getReference()
       .child("articles")
       .child("content")
       .child("ta")
       .child("all")
       .child("KkOz7Zg9iNqms1vZJA6")
       .child("articleTags")
       .addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                @SuppressWarnings("unchecked")
                Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
                String firstValue = (String) map.get("0");
                String secondValue = (String) map.get("1");
                String thirdValue = (String) map.get("2");
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {/*Do Nothing*/}
});

Hope it helps.