当使用Adapter的Filter来过滤数据时，可能会遇到Filter Results始终返回null的情况。这是由于Filter的performFiltering方法没有正确实现。以下是一个正确实现performFiltering方法的示例：

public class MyAdapter extends ArrayAdapter implements Filterable {

    private ArrayList originalList;
    private ArrayList filteredList;
    private MyFilter filter;

    public MyAdapter(Context context, int resource, List objects) {
        super(context, resource, objects);
        this.originalList = new ArrayList(objects);
        this.filteredList = new ArrayList(objects);
    }

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

    @Override
    public String getItem(int position) {
        return filteredList.get(position);
    }

    @Override
    public Filter getFilter() {
        if (filter == null) {
            filter = new MyFilter();
        }
        return filter;
    }

    private class MyFilter extends Filter {

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults results = new FilterResults();
            ArrayList list = new ArrayList(originalList);
            if (constraint == null || constraint.length() == 0) {
                results.values = list;
                results.count = list.size();
            } else {
                String prefix = constraint.toString().toLowerCase();
                final ArrayList newList = new ArrayList();
                for (String item : list) {
                    final String itemName = item.toLowerCase();
                    if (itemName.contains(prefix)) {
                        newList.add(item);
                    }
                }
                results.values = newList;
                results.count = newList.size();
            }
            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            filteredList = (ArrayList) results.values;
            notifyDataSetChanged();
        }
    }
}

上述示例中的performFiltering方法会将原始数据复制到一个新的ArrayList中，并进行过滤处理。如果过滤结果不为空，则将其存储在results.values中并返回，否则返回原始数据列表。在publishResults方法中，过滤结果集合将用于更新