如何使用模型类设置Hashmap值

Question

I want to set Hashmap value using data from database and set it in model class, it doesn't work yet and shows empty data. Here is my code, get Data from database

private ArrayList<Kategori> categories;
private ArrayList<ChatRoom> chatroom_list;
private HashMap<Integer, ArrayList<ChatRoom>> chatrooms;

void getDataList(){
    categories = new ArrayList<>();
    chatrooms = new HashMap<>();
    chatroom_list = new ArrayList<>();
    try{
        categories.clear();
        cursor = db.rawQuery("SELECT * FROM kategori ORDER BY id ASC", null);
        //cursor2 = db.rawQuery("SELECT * FROM chatroom ORDER BY id ASC LIMIT ", null);
        Kategori kategori;
        while (cursor.moveToNext()){
            kategori = new Kategori();
            kategori.setId(cursor.getInt(cursor.getColumnIndex("id")));
            kategori.setNama(cursor.getString(cursor.getColumnIndex("nama")));
            categories.add(kategori);
        }
        listAdapter.notifyDataSetChanged();
    }catch(Exception e){
        e.printStackTrace();
    }
    try{
        chatroom_list.clear();
        chatrooms.clear();
        ChatRoom chatRoom;
        for (int i=0;i<categories.size();i++){
            cursor2 = db.rawQuery("SELECT * FROM chatroom WHERE status = '0' ORDER BY id ASC", null);
            while (cursor2.moveToNext()){
                chatRoom = new ChatRoom();
                chatRoom.setId(cursor2.getInt(cursor2.getColumnIndex("id")));
                chatRoom.setNama(cursor2.getString(cursor.getColumnIndex("nama")));
                chatRoom.setDosen(cursor2.getString(cursor2.getColumnIndex("dosen")));
                chatRoom.setInfo(cursor2.getString(cursor2.getColumnIndex("info")));
                chatRoom.setId_kategori(cursor2.getInt(cursor2.getColumnIndex("id_kategori")));
                if(categories.get(i).getId()==chatRoom.getId_kategori())
                    chatroom_list.add(chatRoom);
            }
            chatrooms.put(categories.get(i).getId(), chatroom_list);
        }
    }catch(Exception e){
        e.printStackTrace();
    }
}

when I check it, Hashmap just shows empty data, Thank you!

Answer 1

I suppose your bug is here:

if(categories.get(i).getId()==chatRoom.getId_kategori())
    chatroom_list.add(chatRoom);

I guess getId() returns Integer , which is an object. Comparing objects with == fails in most cases. When it comes to Integer , it fails once the value is under -128 or over 127 (though this can be overriden. Also there are other circumstances when comparing integers using == can like magically fail or succed. Just don't do it).

Anyhow. Check if getId() returns Integer or Long . If so, change it to categories.get(i).getId().equals(chatRoom.getId_kategori())