java - 过滤器列表在空结果时不会改变

Question

每当过滤 ListView 后没有结果时，我希望它消失并且 TextView 出现在屏幕中央。我知道这一切都需要在 if (results.count == 0) {} 内进行，但我遇到了一些与布局相关的错误，我不知道如何解决。这 '？'应该表示 ListView 的 fragment 布局，但由于代码不在布局类中，我不知道需要用什么来替换它(这同样适用于 ( this) 在 TextView tv = new TextView(this); 中。所有相关帮助将不胜感激。

我想要实现的目标如下:

if (results.count == 0) {

1. Make the list invisible
2. Create a text view programmatically and show it

}

ItemListAdapter 类

public class ItemListAdapter extends BaseAdapter implements Filterable {

    private List<Victoria> mData;
    private List<Victoria> mFilteredData;
    private LayoutInflater mInflater;
    private ItemFilter mFilter;
    private ListView mListView;

    public ItemListAdapter (List<Victoria> data, Context context) {
        mData = data;
        mFilteredData = data;
        mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

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

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

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

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

        ViewHolder holder;
        if (convertView == null) {
           convertView = mInflater.inflate(R.layout.item_row, parent, false);
            holder = new ViewHolder();

            holder.title = (TextView) convertView.findViewById(R.id.item_title);
            holder.description = (TextView) convertView.findViewById(R.id.item_description);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        holder.title.setText(mFilteredData.get(position).getItem());
        holder.description.setText(mFilteredData.get(position).getItemDescription());

        return convertView;
    }

    @Override
    public Filter getFilter() {
        if (mFilter == null) {
            mFilter = new ItemFilter();
        }
        return mFilter;
    }

    /**
     * View holder
     */
    static class ViewHolder {
        private TextView title;
        private TextView description;
    }

    /**
     * Filter for filtering list items
     */
    private class ItemFilter extends Filter {

        /**
         * Invoked on a background thread.  This is where all the filter logic should go
         * @param constraint the constraint to filter on
         * @return the resulting list after applying the constraint
         */
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults results = new FilterResults();

            if (TextUtils.isEmpty(constraint)) {
                results.count = mData.size();
                results.values = mData;
            } else {
                //Create a new list to filter on
                List<Victoria> resultList = new ArrayList<Victoria>();
                for (Victoria str : mData) {
                    if (str.getItemDescription().toLowerCase().contains(constraint.toString().toLowerCase())) {
                        resultList.add(str);
                    }
                }
                results.count = resultList.size();
                results.values = resultList;
            }
            return results;
        }

        /**
         * Runs on ui thread
         * @param constraint the constraint used for the result
         * @param results the results to display
         */
        @SuppressWarnings("unchecked")
        @Override
            protected void publishResults(CharSequence constraint, FilterResults results) {
    if (results.count == 0) {
        //Make list invisible
        //Make text view visible
        notifyDataSetInvalidated();
    } else {
        mFilteredData = (ArrayList<Victoria>)results.values;
        notifyDataSetChanged();
    }
}
    }
}

FilterListFragment 类

public class FilterListFragment extends ListFragment implements SearchView.OnQueryTextListener {



    private ItemListAdapter mAdapter;

    public FilterListFragment() {
        //Required empty constructor
    }

    public static FilterListFragment newInstance() {
        return new FilterListFragment();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_filter_string_list, container, false);
        //Tell the system to call onCreateOptionsMenu
        setHasOptionsMenu(true);
        initialize(view);
        return view;
    }

    List<Victoria> list = new ArrayList<Victoria>();
    private void initialize(View view) {
        String[] items = getActivity().getResources().getStringArray(R.array.items);
        String[] itemDescriptions = getActivity().getResources().getStringArray(R.array.itemDescriptions);
        for (int n = 0; n < items.length; n++){
            Victoria victoria = new Victoria();
            victoria.setID();
            victoria.setItem(items[n]);
            victoria.setItemDescription(itemDescriptions[n]);
            list.add(victoria);
        }

        mAdapter = new ItemListAdapter(list, getActivity());
        setListAdapter(mAdapter);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        // Set up search view
        inflater.inflate(R.menu.menu_search, menu);
        MenuItem item = menu.findItem(R.id.search);
        SearchView searchView = (SearchView) MenuItemCompat.getActionView(item);
        searchView.setOnQueryTextListener(this);
        searchView.setQueryHint(getResources().getString(R.string.search_query));
    }

    @Override
    public boolean onQueryTextSubmit(String newText) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        mAdapter.getFilter().filter(newText);
        return false;
    }
}

Answer 1

您不必处理它，Android 会为您处理。在 fragment_filter_string_list.xml 中添加代表空 View 的 TextView，其 id 为 android:id="@android:id/empty" 。 Android 将根据 getCount() 的值来处理显示/隐藏它。

编辑，

要实现您想要的目标，您的 publishResults 应该如下所示

mFilteredData = (ArrayList<Victoria>)results.values;
notifyDataSetChanged();

您可能还想保留 mFilteredData 的副本，以便在查询更改或重置时恢复数据集