Parse.com获取相同的数据

Question

我有一个从parse.com获取条目的代码。当用户第一次输入片段时，它可以正常工作，但是当用户第二次输入片段时，会多次显示一个条目。

第一次： -

第二次： -

这是我的代码： -

public class ReportHistoryFragment extends Fragment {

    View reportHistory;
    ParseUser parseUser;
    ParseQuery<ParseObject> parseQuery,pq;
    ParseObject parseObject;
    String title,desc;
    Bitmap bitmap;
    ParseFile parseFile;
    Context context;
    Card card;
    ArrayList<Card> cards;
    CardListView cardListView;
    CardArrayAdapter cardArrayAdapter;
    int size,i=0;
    ProgressDialog progressDialog;
    Iterator<ParseObject> iterator;

    public ReportHistoryFragment() {

    **}
    @SuppressLint("ValidFragment")
    public ReportHistoryFragment(Context context) {
        this.context=context;
    }
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        reportHistory = inflater.inflate(R.layout.report_history_layout,container,false);
        cardListView = (CardListView) reportHistory.findViewById(R.id.listcard);
        parseUser = ParseUser.getCurrentUser();
        progressDialog = ProgressDialog.show(context,"Downloading Data","Please wait...",true);
        progressDialog.setCancelable(false);
        downloadData();
        return reportHistory;
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
    @Override
    public void onResume() {
        super.onResume();
    }
    public void downloadData() {
        parseQuery=null;
        pq=null;
        cards = new ArrayList<>();
        parseQuery = ParseQuery.getQuery("Reports");
        parseQuery.whereEqualTo("user",parseUser);
        parseQuery.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> parseObjects, ParseException e) {
                if (e == null) {
                    iterator = parseObjects.iterator();
                    size = parseObjects.size();
                    i=0;
                    while (iterator.hasNext()) {
                        parseObject = iterator.next();
                        pq = ParseQuery.getQuery("Reports");
                        pq.getInBackground(parseObject.getObjectId(), new GetCallback<ParseObject>() {
                            @Override
                            public void done(ParseObject object, ParseException e) {
                                if (e == null) {
                                    title = object.getString("title");
                                    desc = object.getString("description");
                                    parseFile = (ParseFile) object.get("image");
                                    parseFile.getDataInBackground(new GetDataCallback() {
                                        @Override
                                        public void done(byte[] bytes, ParseException e) {
                                            if(e==null) {
                                                bitmap = BitmapFactory.decodeByteArray(bytes,0,bytes.length);
                                            } else {
                                                e.printStackTrace();
                                            }
                                            card = new HistoryItemCard(getActivity(),title,desc,bitmap);
                                            cards.add(card);
                                            i++;
                                            if(i==size) {
                                                cardArrayAdapter = new CardArrayAdapter(getActivity(),cards);
                                                cardArrayAdapter.notifyDataSetChanged();
                                                cardListView.setAdapter(cardArrayAdapter);
                                                progressDialog.dismiss();
                                            }
                                        }
                                    });
                                } else {
                                    e.printStackTrace();
                                }
                            }
                        });
                    }
                } else {
                    e.printStackTrace();
                }
            }
        });
    }
}

请有人帮助我！