Firebase admin java SDK-在事件发生时获取更改数据而不是所有数据

Question

-DB  
  -chat  
     -branches  
      - 1  
      - 2  
        - users  
        - message
         -1  
          - content : "hi",  
          - messageType : "text"  
         -2
          - content : "hello",
          - messageType : "text"
      - 3

ref.child("chat").child("branches").addValueEventListener()

对于分支子项，它只给出2，而消息子项则给出所有消息。如何只获取已更改的邮件子详细信息。

我试图像这样查询chat.branchid.$branchid.message.$messageid

Answer 1

ref.child("chat").child("branches").addChildEventListener(new ChildEventListener() {
  public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
    System.out.println(snapshot.getKey()+" was added after "+previousChildKey);
  }
  public void onChildChanged(DataSnapshot snapshot) {
    System.out.println(snapshot.getKey()+" was changed");
  }
  ...