搜索视图在Android中不起作用.为什么这样

Question

我正在使用应用程序中的标头进行回收视图，并且我正在尝试在应用程序中实现搜索视图，但它不起作用。当我单击搜索视图并键入某些内容时，结果未过滤，我将其放在日志猫中。

2019-06-23 14:00:48.471 27193-27508/com.example.testapp W/Filter: An exception occured during performFiltering()!
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toLowerCase()' on a null object reference
        at com.example.testapp.TitleAdapter$1.performFiltering(TitleAdapter.java:92)
        at android.widget.Filter$RequestHandler.handleMessage(Filter.java:234)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:171)
        at android.os.HandlerThread.run(HandlerThread.java:65)

我已经呆了几个小时了，无法弄清楚我在做什么错。这是我的适配器。

public class TitleAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements Filterable {
    private static final int TYPE_HEADER = 0;
    private static final int TYPE_ITEM = 1;
    private List <ItemObject> list;
    private List <ItemObject> listFiltered;
    private Context context;
    public TitleAdapter(Context context, List <ItemObject> list) {
        this.context = context;
        this.list = list;
        this.listFiltered = list;
    }
    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType == TYPE_HEADER) {
            View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.header_layout, parent, false);
            return new HeaderViewHolder(layoutView);
        } else if (viewType == TYPE_ITEM) {
            View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
            return new ItemViewHolder(layoutView);
        }
        throw new RuntimeException("No match for " + viewType + ".");
    }
    @Override
    public void onBindViewHolder(@NonNull final RecyclerView.ViewHolder holder, int position) {
        ItemObject list = this.list.get(position);
        if (holder instanceof HeaderViewHolder) {
            ((HeaderViewHolder) holder).headerTitle.setText(list.getHeaderTitle());
        } else if (holder instanceof ItemViewHolder) {
            ((ItemViewHolder) holder).titleText.setText(list.getPageName());
        }
    }
    public ItemObject getItem(int position) {
        return list.get(position);
    }
    @Override
    public int getItemCount() {
        return list.size();
    }
    @Override
    public int getItemViewType(int position) {
        if (isPositionHeader(position))
            return TYPE_HEADER;
        return TYPE_ITEM;
    }
    private boolean isPositionHeader(int position) {
        ItemObject mObject = list.get(position);
        return mObject.isHeader();
    }
    @Override
    public Filter getFilter() {
        return new Filter() {
            protected FilterResults performFiltering(CharSequence constraint) {
                if (constraint == null || constraint.length() == 0){
                    listFiltered = list;
                } else {
                    String filterPattern = constraint.toString().toLowerCase().trim();
                    List<ItemObject> lstFilter = new ArrayList<>();
                    for (ItemObject row : list) {
                        // name match condition. this might differ depending on your requirement
                        // here we are looking for name or phone number match
                        if (row.getPageName().toLowerCase().contains(filterPattern)) {
                            lstFilter.add(row);
                        }
                    }
                    listFiltered = lstFilter;
                }
                FilterResults filterResults = new FilterResults();
                filterResults.values = listFiltered;
                return filterResults;
            }
            @Override
            protected void publishResults(CharSequence charSequence, FilterResults results) {
                listFiltered = (List <ItemObject>) results.values;
                // refresh the list with filtered data
                notifyDataSetChanged();
            }
        };
    }
    public class HeaderViewHolder extends RecyclerView.ViewHolder {
        TextView headerTitle;
        public HeaderViewHolder(View itemView) {
            super(itemView);
            headerTitle =  itemView.findViewById(R.id.headerText);
        }
    }
    public class ItemViewHolder extends RecyclerView.ViewHolder{
        TextView titleText;
        public ItemViewHolder(View itemView) {
            super(itemView);
            titleText = itemView.findViewById(R.id.titleText);
            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int position = getAdapterPosition();
                    Intent intent = new Intent(context, ViewerActivity.class);
                    intent.putExtra("PageName",list.get(position).getPageName());
                    intent.putExtra("PageUrl",list.get(position).getPageUrl());
                    context.startActivity(intent);
                }
            });
        }
    }
}

顺便说一句，如果您想知道这是第92行

 if (row.getPageName().toLowerCase().contains(filterPattern)) {
                            lstFilter.add(row);
                        }

Answer 1

如您所知，null在getPageName()上有例外，因此只需检查

if(row.getPageName()!=null && !row.getPageName().isEmpty())
 if (row.getPageName().toLowerCase().contains(filterPattern)) {
                            lstFilter.add(row);
                        }

我看到您在getItemCount()中有list对象，因此我认为主要"列表"是list，因此您必须备份此对象，并且在此行中执行以下操作：

            @Override
            protected void publishResults(CharSequence charSequence, FilterResults results) {
                //listFiltered = (List <ItemObject>) results.values;
                //back up `list` some where else for reloading the list without filter
                list.clear();
                list.addAll((List <ItemObject>) results.values);
                // refresh the list with filtered data
                notifyDataSetChanged();
            }

备份主数据并将过滤器放入