carl's questions

我在应用程序中的自定义列表视图中实现了搜索功能。问题是我遇到了这个错误（仅在实体手机上出现，虚拟机上没有）：

java.lang.NullPointerException：尝试在空对象引用上调用接口方法“int java.util.List.size()”

我不明白为什么在虚拟设备上搜索功能运行良好。问题出在哪里？

这是我的代码：

CustomAdapterShoppingList班级：

public class CustomAdapterShoppingList extends BaseAdapter implements Filterable {

    List<Product> list;
    List<Product> listFiltered;
    Context mContext;

    public CustomAdapterShoppingList(@NonNull Context context, List<Product> products) {
        this.list = products;
        this.listFiltered = products;
        this.mContext = context;
    }

    @Override
    public int getCount() {
        return listFiltered.size();  <---- THE ERROR mentioned above
    }

    @Override
    public Product getItem(int position) {
        return listFiltered.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    private int lastPosition = -1;

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(R.layout.shoplist_row, parent,
                    false);
        }
        Animation animation = AnimationUtils.loadAnimation(mContext, (position > lastPosition)
                ? R.anim.up_from_bottom : R.anim.down_from_top);
        convertView.startAnimation(animation);
        lastPosition = position;

            TextView number = convertView.findViewById(R.id.number);
            number.setText(position + 1 + ".");

            TextView name = convertView.findViewById(R.id.name);
            name.setText(listFiltered.get(position).getProduktName());
            
        return convertView;
    }

    @Override
    public Filter getFilter() {
        Filter filter = new Filter() {
            @Override
            protected FilterResults performFiltering(CharSequence charSequence) {
                FilterResults filterResults = new FilterResults();
                if (list == null) {
                    list = new ArrayList<>(listFiltered);
                }

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.VANILLA_ICE_CREAM) {
                    if (charSequence == null || charSequence.isEmpty()) {
                        filterResults.count = list.size();
                        filterResults.values = list;
                    } else {
                        List<Product> resultPrd = new ArrayList<>();
                        String searchStr = charSequence.toString().toLowerCase();

                        for (Product prd:list) {
                            if(prd.getProduktName().contains(searchStr)) {
                                resultPrd.add(prd);
                            }
                            filterResults.count = resultPrd.size();
                            filterResults.values = resultPrd;
                        }
                    }
                }
                return filterResults;
            }

            @SuppressWarnings("unchecked")
            @Override
            protected void publishResults(CharSequence charSequence, FilterResults filterResults) {

                listFiltered = (List<Product>) filterResults.values;
                notifyDataSetChanged();
            }
        };
        return filter;
    }
}

然后，使用以下代码调用类中的搜索功能ShoppinglistActivity：

adapter = new CustomAdapterShoppingList(getApplicationContext(), products);
                shoppingList.setAdapter(adapter);
                adapter.notifyDataSetChanged();
                sv.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
                    @Override
                    public boolean onQueryTextSubmit(String query) {
                        return false;
                    }
                    @Override
                    public boolean onQueryTextChange(String newText) {
                        adapter.getFilter().filter(newText);
                        return false;
                    }
                });