这将有助于了解您实际如何处理 onDataChange 中的数据.但我的猜测是你没有遍历孩子:

It would help to see how you actually handle the data in onDataChange. But my guess is that you're failing to loop over the children:

mDatabase
  .child("projects")
  .orderByChild("dateAdded")
  .addValueEventListener(new ValueEventListener() {
    public void onDataChange(DataSnapshot snapshot) {
      for (DataSnapshot child: snapshot.getChildren()) {
        System.out.println(child.getKey());
      }
    }
    ...