由于将值设置为15时将获得最后15位数字，因此将limitToLast值更改为-1即可获得最新的Firebase值. 将您的代码更改为以下代码段.

Since you're getting the last 15 digits when you set the value to 15, change the limitToLast value to -1 to get the last Firebase value. Change your code to below snippet.

messagesListener = FBMessagesRef.limitToLast(-1).addChildEventListener(new ChildEventListener(),