NotifyDataSetChanged() 未显示更新的列表

Question

I get correct objects in filtered list in publishResults() function but the filtered list is not displayed on the screen after filtering. Following is the code for CityAdapter class inhereted from ArrayAdapter class. IT seems like notifyDataSetChanged() isn't working? Please inform why list is not displaying.What's wrong in the code.

import...
public class CityListAdapter extends ArrayAdapter<City> implements Filterable {

    private ArrayList<City> cities;
    private ArrayList<City> filtered_list;

    public CityListAdapter(Context context, int resource, ArrayList<City>cities) {
        super(context, resource, cities);
        this.cities = cities;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView,  ViewGroup parent) {

        Holder holder = new Holder();
        if(convertView == null) {
            LayoutInflater inflator = LayoutInflater.from(getContext());
            convertView = inflator.inflate(R.layout.adapter_view,parent,false);


            holder.box = (CheckBox) convertView.findViewById(R.id.checkBox);
            holder.name = (TextView) convertView.findViewById(R.id.textView);

            convertView.setTag(holder);
        }
        else {
            holder = (Holder) convertView.getTag();
        }
        City city = getItem(position) ;
        holder.name.setText(city.getName());

        return convertView;
    }
    private class Holder {
        CheckBox box;
        TextView name;


    }
    @NonNull
    @Override
    public Filter getFilter() {
        return new CityFilter();
    }



    private class CityFilter extends Filter {

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {

            FilterResults results = new FilterResults();

            filtered_list = new ArrayList<>();
            if (constraint != null && constraint.length()!= 0) {
                for (int i = 0; i < cities.size(); i++) {
                    if (cities.get(i).getName().contains(constraint)) {
                        filtered_list.add(cities.get(i));
                        showMessage(cities.get(i).getName() + "added");
                    }
                }
            }
            results.values = filtered_list;
            results.count = filtered_list.size();


            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            filtered_list = (ArrayList<City>) results.values;
            int size =filtered_list.size();
            showMessage("Data set changed"+String.format("%d", size));
            notifyDataSetChanged();
        }

    }
    public void showMessage(String message) {
        Toast toast = Toast.makeText(getContext(), message, Toast.LENGTH_LONG);
        toast.show();
    }

}

Answer 1

You need to have a full list of items in the very beginning (ie in the constructor) assigned to the filtered list; so that they can have the entire list when there is no filtering of results (empty search) and that occurs whenever you instantiate the adapter.

public CityListAdapter(Context context, int resource, ArrayList<City>cities) {
    super(context, resource, cities);
    this.cities = cities;
    this.filtered_list = cities; // <<<<< Change here
}

Side Note

Also override getCount() to avoid IndexOutOfBoundsException when reaching the end of the list on scroll whenever the original list size not equal to the filtered list size.

As the original list is cities , when you make filtering, its size will shrink down, so you need only to get the filtered list size not the original list size to avoid IndexOutOfBoundsException .

So add this to the adapter:

@Override
public int getCount() {
    return filtered_list.size();
}