Weird behaviour trying to retrieve data with SQLite while on AsyncTask

Issue

My app was very laggy, so I decided to use an AsyncTask to do the heaviest operations inside it and so, the app wouldn't be so slow at changing tabs.
But now, it is behaving in a very weird way. Let me explain: I have a ViewPager2, and inside that ViewPager, I have a recyclerview. I put an AsyncTask inside the ViewPager, because it is the heaviest operation done in the fragment, and in the adapter of that ViewPager, I retrieve some values from a Database via a class called DatabaseHelper which one that extends SQLiteOpenHelper and has this method.

public Cursor getAllTasksByList(int ListID)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor c = db.rawQuery("SELECT * FROM " + Db.Tables.Tasktable.TASKS_TABLE + " WHERE " + Db.Tables.Tasktable.COL_LIST_ID + " = " + ListID, null);
        return c;
    }

Because the DatabaseHelper only returns one Cursor, I use another class to keep the code organized, this class takes the Cursor as argument and returns a list of "ListItem". This class is called "FolderUtils" and contains the following method (which one that I use to populate my RecyclerView inside that is inside my ViewPager):

public ArrayList<TaskItem> getTasksByList(int ListID, Context context) {    
        ArrayList<TaskItem> tasks = new ArrayList<>();
        DatabaseHelper d = new DatabaseHelper(context);
        Cursor c = d.getAllTasksByList(ListID);

        while (c.moveToNext()) {
            int id = c.getInt(0);
            int listid = c.getInt(1);
            boolean checked = c.getInt(2) > 0;
            String title = c.getString(3);

            tasks.add(new TaskItem(id, listid, checked, title));
        }

        return tasks;
    }

But here it is the problem, sometimes this List is empty, but another times, it just retrieves the first value of the that Table I look for, strangely, sometimes it returns wrong values and it only works sometimes if I move my ViewPager to another position or if I just put some breakpoints. Here is my Adapter code.

@Override
    public void onBindViewHolder(@NonNull ListHolder holder, int position) {
        new LoadData(mList.get(position), holder).execute();
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }


    private class LoadData extends AsyncTask<Void, Void, Void> {

        private ListItem item;
        private ListHolder holder;

        public LoadData(ListItem item, ListHolder holder) {
            this.item = item;
            this.holder = holder;
        }

        @Override
        protected void onPreExecute(){
            super.onPreExecute();
            //I set the visibility to GONE so that the user can just see the final layout and not the layout "Building" itself.
            holder.itemView.setVisibility(View.GONE);
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            setItems(item, holder); //setItems is for setting the UI Content.
            AttachRecycler(holder, item); //AttachRecycler creates an adapter for the recyclerview with the TaskList values, and attaches it to the recyclerview inside the ViewPager item.
            holder.itemView.setVisibility(View.VISIBLE); //Shows the finished item
        }

        @Override
        protected Void doInBackground(Void... voids) {
            SetList(item); //SetList is where it takes the values from database and adds it to the list.
            return null;
        }
    }

private void SetList(ListItem item) {
        TaskList = new ArrayList<>();

        else if (Mode == 1)
        {
            //Mode by default is 1. The line below does gets executed, however, it returns the wrong values.
            TaskList.addAll(FolderUtils.getInstance().getTasksByList(item.getID(), context));
        }

private void AttachRecycler(ListHolder holder, ListItem item)
    {
        LinearLayoutManager manager = new LinearLayoutManager(context);
        holder.recycler.setLayoutManager(manager);
        adapter = new TaskAdapter(TaskList, item.getColor(), context, item.getID());
        holder.recycler.setAdapter(adapter);

    }

How could I fix this? Thank You.

Solution

Solved this by myself. Solution was to make TaskList a private variable inside the LoadData class, not a private variable of the entire Adapter, this acts like a local variable for every item instance, removing the duplicates in some items.

Answered By - RushedPotato