How can I delete duplicate items in ArrayList <Object> with LinkedHashSet?

Question

I have been trying many things to solve this problem and searching for the solution for hours, I need some help with this. I have a listview, importing data from MySQL and fetching data in Listview. My problem: the listview duplicate items (Only the first 20, then I use "loadmoredata" and I receive on scroll downn new 20 items, but no more duplicated items again). So, the first time I see 40 items (20 repeated).

I have tried LinkedHashSet but I cant get that works. Any suggestions?

private ArrayList<Usuarios> items;
private Set<Usuarios> set;
private ArrayList<Usuarios> newList;
Activity activity;
Usuarios_adapter adapter;

...

listView = (ListView) findViewById(R.id.listView);
    listView.setOnItemClickListener(this);

    activity=this;
    items=new ArrayList<Usuarios>();
    set = new LinkedHashSet<Usuarios>(items);
    newList = new ArrayList<Usuarios>(set);
    adapter=new Usuarios_adapter(activity,newList);
    listView.setAdapter(adapter);

    //more code here

    }
    class BackTask extends AsyncTask<Void,Void,Void>{

    protected void onPreExecute(){
        super.onPreExecute();
        listView.addFooterView(footerView);

    }
    protected Void doInBackground(Void...params) {
        HashMap<String,String> params2 = new HashMap<>();
        params2.put(Config.TAG_PESO,lastpeso2);
        RequestHandler rh = new RequestHandler();
        String s = rh.sendPostRequest(Config.URL_GET_ALL3, params2);
        JSON_STRING = s;
        JSONObject jsonObject = null;
        try {
            if(isLoadMore){
            isLoadMore = false; }
            jsonObject = new JSONObject(JSON_STRING);
            JSONArray result = jsonObject.getJSONArray(Config.TAG_JSON_ARRAY);

            for (int i = 0; i < result.length(); i++) {
                JSONObject jo = result.getJSONObject(i);
                String id = String.valueOf(jo.getInt(Config.TAG_ID));
                String nombre = jo.getString(Config.TAG_NOMBRE);
                String email = jo.getString(Config.TAG_EMAIL);
                String foto = jo.getString(Config.TAG_FOTO);
                String peso = jo.getString(Config.TAG_PESO);
                String vasos = jo.getString(Config.TAG_VASOS);
                String seguimiento = jo.getString(Config.TAG_SEGUIMIENTO);
                String aplausos = jo.getString(Config.TAG_APLAUSOS);
                String followers = jo.getString(Config.TAG_FOLLOWERS);

                Usuarios user = new Usuarios(id, nombre, email, foto, peso, vasos, seguimiento ,aplausos, followers);
                //items.add(user); //this would be the original, who give me duplicated items

                newList.add(user);//this is the second arraylist

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }


    protected void onPostExecute(Void result){
        listView.removeFooterView(footerView);
        adapter.notifyDataSetChanged(); 




    }
}
    BackTask bt = new BackTask();
    bt.execute();

EDIT: With @Japu_D_Cret modification

    private ArrayList<Usuarios> items;
    private Activity activity;
    private Usuarios_adapter adapter;

    .....

    activity=this;
    items=new ArrayList<Usuarios>();
    adapter=new Usuarios_adapter(activity,items);
    listView.setAdapter(adapter);

    ....

     Set<Usuarios> set = new HashSet<>(items);

            for (int i = 0; i < result.length(); i++) {
                JSONObject jo = result.getJSONObject(i);
                String id = String.valueOf(jo.getInt(Config.TAG_ID));
                String nombre = jo.getString(Config.TAG_NOMBRE);
                String email = jo.getString(Config.TAG_EMAIL);
                String foto = jo.getString(Config.TAG_FOTO);
                String peso = jo.getString(Config.TAG_PESO);
                String vasos = jo.getString(Config.TAG_VASOS);
                String seguimiento = jo.getString(Config.TAG_SEGUIMIENTO);
                String aplausos = jo.getString(Config.TAG_APLAUSOS);
                String followers = jo.getString(Config.TAG_FOLLOWERS);

                Usuarios user = new Usuarios(id, nombre, email, foto, peso, vasos, seguimiento ,aplausos, followers);
                //items.add(user);
                set.add(user);


            }
            //clear the list, so no duplicates occurr
            items.clear();
            //copy the temporary set to the items
            items.addAll(set);
            } catch (JSONException e) {
                e.printStackTrace();
        }
        return null;
    }

And this is my getView

      public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        LayoutInflater inflator = activity.getLayoutInflater();
        convertView = inflator.inflate(R.layout.b_server_list_item, null);
        holder = new ViewHolder();
        holder.id = (TextView) convertView.findViewById(R.id.id);
        holder.email = (TextView) convertView.findViewById(R.id.list_email);
        holder.nombre = (TextView) convertView.findViewById(R.id.Nombre);
        holder.peso = (TextView) convertView.findViewById(R.id.Peso);
        holder.vasos = (TextView) convertView.findViewById(R.id.Vasos);
        holder.seguimiento = (TextView) convertView.findViewById(R.id.Seguimiento);
        holder.followers = (TextView) convertView.findViewById(R.id.tv_followers);
        holder.aplausos = (TextView) convertView.findViewById(R.id.tv_aplausos);
        holder.picture = (ImageView) convertView.findViewById(R.id.foto_profile);
        holder.foto_id = (TextView) convertView.findViewById(R.id.foto_id);
        holder.rank = (TextView) convertView.findViewById(R.id.Rank);
        holder.picture = (ImageView) convertView.findViewById(R.id.foto_profile);
        convertView.setTag(holder);

    } else {

        holder = (ViewHolder) convertView.getTag();
    }

    holder.id.setText(items.get(position).getId());
    holder.email.setText(items.get(position).getEmail());
    holder.nombre.setText(items.get(position).getNombre());
    holder.peso.setText(items.get(position).getPeso());
    holder.vasos.setText(items.get(position).getVasos());
    holder.seguimiento.setText(items.get(position).getSeguimiento());
    holder.followers.setText(items.get(position).getFollowers());
    holder.aplausos.setText(items.get(position).getAplausos());
    holder.foto_id.setText(items.get(position).getFoto());
    final int pos = position+1;
    holder.rank.setText("" + pos);

    String fotoid = holder.foto_id.getText().toString();
    if(fotoid.contains("avatar_a")){holder.picture.setImageResource(R.drawable.avatar_a);}
    if(fotoid.contains("avatar_b")){holder.picture.setImageResource(R.drawable.avatar_b);}

     return convertView;
}

you do not use the Set. you copy the contents to newList, but don't actually use it. see my answer below — Japu_D_Cret
– Japu_D_Cret, Commented Mar 25, 2017 at 18:18

Japu_D_Cret · Accepted Answer · 2017-03-25 18:52:15Z

2

in these lines, you first create a an ArrayList items, then copy it's content to a Set set, then copy the Sets content in a new ArrayList newlist

items=new ArrayList<Usuarios>();
set = new LinkedHashSet<Usuarios>(items);
newList = new ArrayList<Usuarios>(set);

i would remove all unnecessary lists and only go with the Set, so your code will look like this

//private ArrayList<Usuarios> items;
private Set<Usuarios> set;
//private ArrayList<Usuarios> newList;

//...

protected Void doInBackground(Void...params) {
    HashMap<String,String> params2 = new HashMap<>();
    params2.put(Config.TAG_PESO,lastpeso2);
    RequestHandler rh = new RequestHandler();
    String s = rh.sendPostRequest(Config.URL_GET_ALL3, params2);
    JSON_STRING = s;
    JSONObject jsonObject = null;
    try {
        if(isLoadMore){
        isLoadMore = false; }
        jsonObject = new JSONObject(JSON_STRING);
        JSONArray result = jsonObject.getJSONArray(Config.TAG_JSON_ARRAY);

        for (int i = 0; i < result.length(); i++) {
            JSONObject jo = result.getJSONObject(i);
            String id = String.valueOf(jo.getInt(Config.TAG_ID));
            String nombre = jo.getString(Config.TAG_NOMBRE);
            String email = jo.getString(Config.TAG_EMAIL);
            String foto = jo.getString(Config.TAG_FOTO);
            String peso = jo.getString(Config.TAG_PESO);
            String vasos = jo.getString(Config.TAG_VASOS);
            String seguimiento = jo.getString(Config.TAG_SEGUIMIENTO);
            String aplausos = jo.getString(Config.TAG_APLAUSOS);
            String followers = jo.getString(Config.TAG_FOLLOWERS);

            Usuarios user = new Usuarios(id, nombre, email, foto, peso, vasos, seguimiento ,aplausos, followers);
            //items.add(user); //this would be the original, who give me duplicated items

            //newList.add(user);//this is the second arraylist

            set.add(user);
        }
    } catch (JSONException e) {
        e.printStackTrace();
    }
    return null;
}

after your feedback i altered it, so it only uses a Set inside the function:

private ArrayList<Usuarios> items;
//private Set<Usuarios> set;
//private ArrayList<Usuarios> newList;

//...

protected Void doInBackground(Void...params) {
    HashMap<String,String> params2 = new HashMap<>();
    params2.put(Config.TAG_PESO,lastpeso2);
    RequestHandler rh = new RequestHandler();
    String s = rh.sendPostRequest(Config.URL_GET_ALL3, params2);
    JSON_STRING = s;
    JSONObject jsonObject = null;
    try {
        if(isLoadMore){
        isLoadMore = false; }
        jsonObject = new JSONObject(JSON_STRING);
        JSONArray result = jsonObject.getJSONArray(Config.TAG_JSON_ARRAY);

        //make a temporary copy
        Set<Usuarios> set = new HashSet<>(items);

        for (int i = 0; i < result.length(); i++) {
            JSONObject jo = result.getJSONObject(i);
            String id = String.valueOf(jo.getInt(Config.TAG_ID));
            String nombre = jo.getString(Config.TAG_NOMBRE);
            String email = jo.getString(Config.TAG_EMAIL);
            String foto = jo.getString(Config.TAG_FOTO);
            String peso = jo.getString(Config.TAG_PESO);
            String vasos = jo.getString(Config.TAG_VASOS);
            String seguimiento = jo.getString(Config.TAG_SEGUIMIENTO);
            String aplausos = jo.getString(Config.TAG_APLAUSOS);
            String followers = jo.getString(Config.TAG_FOLLOWERS);

            Usuarios user = new Usuarios(id, nombre, email, foto, peso, vasos, seguimiento ,aplausos, followers);
            //items.add(user); //this would be the original, who give me duplicated items

            //newList.add(user);//this is the second arraylist

            set.add(user);
        }

        //clear the list, so no duplicates occurr
        list.clear();
        //copy the temporary set to the items
        list.addAll(set);
    } catch (JSONException e) {
        e.printStackTrace();
    }
    return null;
}

edited Mar 25, 2017 at 18:52

answered Mar 25, 2017 at 18:17

Japu_D_Cret

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7 Comments

SanHappy Over a year ago

I tried. If I do that I receive 0 items and crash. I need at least private ArrayList<Usuarios> items because I have to use it in the adapter adapter=new Usuarios_adapter(activity,items); I deleted the innecesary second arraylist but still doesn´t work

SanHappy Over a year ago

Bad lucky again. Now a receive 40 items again. I tried with HashSet like you said me and then with LinkedHashSet because I need the respect the order but both give me 40 item (20 repeated).

Japu_D_Cret Over a year ago

@SanHappy can you edit your question and add how your code looks now? maybe jsut a small typo now :)

SanHappy Over a year ago

I inserted my getView

Japu_D_Cret Over a year ago

@SanHappy ok, a Set can only determine if an object is a duplicate if you override the equals method(so your Usuarios class should override it and check with the primary key(i.e. ID)), see this for reference stackoverflow.com/questions/16462644/…

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