Firebase数据库如何从节点创建列表，如WhatsApp聊天页面

Question

我想创建与Firebase数据库的聊天应用程序。我正在阅读文档和看教程，但有一件事我不知道该怎么做。当用户向其他用户发送消息时，使用密钥创建聊天室：“senderUserId_receiverUserId”
您可以在下面看到我的结构。

{ 
    "chat_rooms" : { 
    "nTAHqCTmLRcLOM8CTfnHF4lRjLf2_oTLYaHMOMibh3ZqOcmpcWDtSCKp1" : { 
     "-KtQEGK38lhZrgnNxmqb" : { 
     "date" : "07/09/2017 10:28", 
     "message" : “Thanks for helping !”, 
     "photoUrl" : "http://www.clker.com/cliparts/B/R/Y/m/P/e/blank-profile-hi.png", 
     "receiverName" : "Ali”, 
     "receiverUid" : "oTLYaHMOMibh3ZqOcmpcWDtSCKp1", 
     "senderName" : “John”, 
     "senderUid" : "nTAHqCTmLRcLOM8CTfnHF4lRjLf2" 
     }, 
     "-KtQEKK2BmIMzwruN-21" : { 
     "date" : "07/09/2017 10:28", 
     "message" : “Another Test Message“, 
     "photoUrl" : "http://www.clker.com/cliparts/B/R/Y/m/P/e/blank-profile-hi.png", 
     "receiverName" : “John”, 
     "receiverUid" : "nTAHqCTmLRcLOM8CTfnHF4lRjLf2", 
     "senderName" : "Ali", 
     "senderUid" : "oTLYaHMOMibh3ZqOcmpcWDtSCKp1" 
     }, 
     "-KtQIGDk5zE4JZuE9pIQ" : { 
     "date" : "07/09/2017 10:45", 
     "message" : “Test message !“, 
     "photoUrl" : "http://www.clker.com/cliparts/B/R/Y/m/P/e/blank-profile-hi.png", 
     "receiverName" : “John”, 
     "receiverUid" : "nTAHqCTmLRcLOM8CTfnHF4lRjLf2", 
     "senderName" : "Ali", 
     "senderUid" : "oTLYaHMOMibh3ZqOcmpcWDtSCKp1" 
     } 
    } 
    }, 
    "users" : { 
    "nTAHqCTmLRcLOM8CTfnHF4lRjLf2" : { 
     "address" : “istanbul”, 
     "cell_phone" : “none”, 
     "email" : “john@gmail.com", 
     "home_phone" : “none”, 
     "name" : “John”, 
     "photoUrl" : "http://www.clker.com/cliparts/B/R/Y/m/P/e/blank-profile-hi.png", 
     "userId" : "nTAHqCTmLRcLOM8CTfnHF4lRjLf2" 
    }, 
    "oTLYaHMOMibh3ZqOcmpcWDtSCKp1" : { 
     "address" : “istanbul”, 
     "cell_phone" : “none”, 
     "email" : "ali@gmail.com”, 
     "home_phone" : “none”, 
     "name" : "Ali", 
     "photoUrl" : "http://www.clker.com/cliparts/B/R/Y/m/P/e/blank-profile-hi.png", 
     "userId" : "oTLYaHMOMibh3ZqOcmpcWDtSCKp1" 
    } 
    } 
} 

有了这样一切工作正常，但我不知道如何在例如WhatsApp的聊天页面列表列出用户的所有对话。我的意思是当用户点击对话项目时，相关的对话将会打开。
我发送私人邮件与下面的代码：

public void sendMessageToFirebaseUser(final Context context, final ChatMessageModel chat, final String receiverFirebaseToken) { 

     final String room_type_1 = chat.getSenderUid() + "_" + chat.getReceiverUid(); 
     final String room_type_2 = chat.getReceiverUid() + "_" + chat.getSenderUid(); 

     final DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference(); 

     databaseReference.child(Constants.ARG_CHAT_ROOMS) 
       .getRef() 
       .addListenerForSingleValueEvent(new ValueEventListener() { 
        @Override 
        public void onDataChange(DataSnapshot dataSnapshot) { 
         if (dataSnapshot.hasChild(room_type_1)) { 
          Log.e("aaa", "sendMessageToFirebaseUser: " + room_type_1 + " exists"); 
          databaseReference.child(Constants.ARG_CHAT_ROOMS) 
            .child(room_type_1) 
            .push() 
            .setValue(chat); 
         } else if (dataSnapshot.hasChild(room_type_2)) { 
          Log.e("aaa", "sendMessageToFirebaseUser: " + room_type_2 + " exists"); 
          databaseReference.child(Constants.ARG_CHAT_ROOMS) 
            .child(room_type_2) 
            .push() 
            .setValue(chat); 
         } else { 
          Log.e("aaa", "sendMessageToFirebaseUser: success"); 
          databaseReference.child(Constants.ARG_CHAT_ROOMS) 
            .child(room_type_1) 
            .push() 
            .setValue(chat); 
         } 
        } 

        @Override 
        public void onCancelled(DatabaseError databaseError) { 

        } 
       }); 
    } 

感谢您阅读我的文章。

Answer 1

如果您想要显示当前用户的聊天室列表，您应该对您的数据建模以允许这样做。最简单的方法是将每个用户的聊天室列表添加到您的数据模型中：

"userChatrooms" : { 
    "nTAHqCTmLRcLOM8CTfnHF4lRjLf2" : { 
    "nTAHqCTmLRcLOM8CTfnHF4lRjLf2_oTLYaHMOMibh3ZqOcmpcWDtSCKp1": true 
    }, 
    "oTLYaHMOMibh3ZqOcmpcWDtSCKp1" : { 
    "nTAHqCTmLRcLOM8CTfnHF4lRjLf2_oTLYaHMOMibh3ZqOcmpcWDtSCKp1": true 
    } 
}