Android : Expandable list adapter

Question

I've got problem with adapter to present data. I've got object with few list inside it and need to display data from them. I need to present :

date * flight number * duration * regular fare price with currency

and here are my model classes :

 public class Currency implements Serializable {

        private String currency;
        private Integer currPrecision;
        private List<Trip> trips = null;
        private String serverTimeUTC;

public class Trip {

    private String origin;
    private String originName;
    private String destination;
    private String destinationName;
    private List<Date> dates = null;

public class Date {
private String dateOut;
private List<Flight> flights = null;

public class Flight {
private String flightNumber;
private List<String> time = null;
private List<String> timeUTC = null;
private String duration;
private Integer faresLeft;
private String flightKey;
private Integer infantsLeft;
private RegularFare regularFare;
private BusinessFare businessFare;
private LeisureFare leisureFare;

I try to deal it with expandable list adapter but no succeeded. Here's my adapter class :

public class MyExpandableAdapter extends BaseExpandableListAdapter {

private Activity activity;
private ArrayList<ArrayList<Flight>> childtems;
private LayoutInflater inflater;
private ArrayList<Date> parentItems;
private ArrayList<Flight> child;

public MyExpandableAdapter(ArrayList<Date> parents,ArrayList<ArrayList<Flight>> childern) {
    this.parentItems = parents;
    this.childtems = childern;
}

public void setInflater(LayoutInflater inflater, Activity activity) {
    this.inflater = inflater;
    this.activity = activity;
}

@Override
public View getChildView(int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

    child = (ArrayList<Flight>) childtems.get(groupPosition);

    TextView textView = null;

    if (convertView == null) {
        convertView = inflater.inflate(R.layout.result_row, null);
    }

    textView = (TextView) convertView.findViewById(R.id.listTitle);
    textView.setText(child.get(childPosition).getDuration());

    convertView.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View view) {

        }
    });

    return convertView;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {

    if (convertView == null) {
        convertView = inflater.inflate(R.layout.result_row, null);
    }

    ((CheckedTextView) convertView).setText(parentItems.get(groupPosition).getDateOut());
    ((CheckedTextView) convertView).setChecked(isExpanded);

    return convertView;
}

@Override
public Object getChild(int groupPosition, int childPosition) {
    return null;
}

@Override
public long getChildId(int groupPosition, int childPosition) {
    return 0;
}

@Override
public int getChildrenCount(int groupPosition) {
    return ((ArrayList<Flight>) childtems.get(groupPosition)).size();
}

@Override
public Object getGroup(int groupPosition) {
    return null;
}

@Override
public int getGroupCount() {
    return parentItems.size();
}

@Override
public void onGroupCollapsed(int groupPosition) {
    super.onGroupCollapsed(groupPosition);
}

@Override
public void onGroupExpanded(int groupPosition) {
    super.onGroupExpanded(groupPosition);
}

@Override
public long getGroupId(int groupPosition) {
    return 0;
}

@Override
public boolean hasStableIds() {
    return false;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
    return false;
}

}

My Activity class:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_result);
        ButterKnife.bind(this);
        if(getIntent() != null) {
            Intent intent = getIntent();
            String currencyString = intent.getStringExtra("Currency");
            Gson gson = new Gson();
            Currency currency = gson.fromJson(currencyString, Currency.class);
            trips = new ArrayList<>();
            trips = currency.getTrips();
            for(Trip trip :trips) {
                ArrayList<Date> date = trip.getDates();
                dates=date;
                for(Date dateFlight: dates) {
                   flights.add(dateFlight.getDateOut());
                }
            }
            adapter = new MyExpandableAdapter(dates,flights);
            mTripsRv.setAdapter(adapter);

        }

Thanks in advance for help!! :)