java - 在扩展 Base Adapter 的类的对象上调用 notifyDataSetChanged() 时会发生什么

Question

我正在审查 Android 上的代码，但不明白在扩展 BaseAdapter 的类的对象上调用 notifyDataSetChanged() 时发生了什么。在代码中，调用了 channelListAdapter.notifyDataSetChanged()。

这是 ChannelListAdapter 类的代码:

 public class ChannelListAdapter extends BaseAdapter {

    Field[] fields;
    Context context;
    List<Channels> channelList = null;
    String dateString, likeData, ab, imageData;
    Channels item;
    DBVideos dbVideos;
    VideoListAdapter videoListAdapter;
    MostRecentFragment parentFragment;
    public boolean loadingMoreChannels;
    public boolean noMoreChannelFound;
    Map<String, Boolean> map = new HashMap<String, Boolean>();
    Map<String, Integer> totalLikeCount = new HashMap<String, Integer>();
    public Map<String, Boolean> timerMap = new HashMap<String, Boolean>();
    Map<String, List<Videos>> mapVideos = new HashMap<String, List<Videos>>();

    public ChannelListAdapter(Context context) {
        this.context = context;
    }

    public Map<String, List<Videos>> getMapVideos() {
        return mapVideos;
    }

    public void setMapVideos(Map<String, List<Videos>> mapVideos) {
        this.mapVideos = mapVideos;
    }

    public ChannelListAdapter(Context context, List<Channels> channelList) {
        this.context = context;
        // listener = new NewsFeedListener(context, map, totalLikeCount);
        // listener.setListAdapter(this);
        this.channelList = channelList;
    }

    public ChannelListAdapter(Context context, List<Channels> channelList, MostRecentFragment parentFragment) {
        this.context = context;
        this.parentFragment = parentFragment;
        this.channelList = channelList;
    }

    public String getLastFeedModificationTime() {
        Channels lastNews = channelList.get(channelList.size() - 1);
        return lastNews.getLastModifyDate();
    }

    public void setNewsList(List<Channels> channelList) {
        this.channelList = channelList;
    }

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

    @Override
    public Object getItem(int position) {
        return channelList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return channelList.indexOf(getItem(position));
    }

    public static class ViewHolder {
        public TextView channelTitle;
        public ImageView imgProcess;
        ListView videoListView;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = new ViewHolder();
        LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);

        if (convertView == null) {
            convertView = (View) mInflater.inflate(R.layout.channel_list_item, null);
            holder.channelTitle = (TextView) convertView.findViewById(R.id.tv_channel_name);
            holder.imgProcess = (ImageView) convertView.findViewById(R.id.img_process);
            holder.videoListView = (ListView) convertView.findViewById(R.id.list_videos);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        item = (Channels) getItem(position);
        final ViewHolder finalHolder = holder;
        holder.channelTitle.setText(item.getTitle());
        if (mapVideos.size() > 0 && mapVideos.containsKey(item.getId())) {

        } else {
            Glide.with(context).load("http://4.bp.blogspot.com/-rSoHhekcu9A/T6PQ6d8mKSI/AAAAAAAAASg/hStx9Mg18fc/s1600/22.gif").asGif().placeholder(R.drawable.img_loading).crossFade()
                    .into(holder.imgProcess);
            String url = null;
            url = context.getString(R.string.url_6e_channel_context)+CommonUtils.getEncodedUrl(context, context.getString(R.string.url_to_retive_all_video_selected_channel_first)+item.getId())+"+ContentType:Indigo+Video'&rowlimit=3&"+CommonUtils.getEncodedUrl(context,context.getString(R.string.url_to_retive_all_video_selected_channel_sec));
            System.out.println("url ="+url);
            ServiceCallAsync sca = new ServiceCallAsync(context, null,"Get", null, url, new AsyncResponse() {
                @Override
                public void processFinish(Object output) {
                    ServiceResponse serviceResponse = (ServiceResponse) output;
                    if(serviceResponse.getCode()==200){
                        parseDataAndStoreinDb(serviceResponse.getData(),finalHolder);
                    }else{

                    }

                }
            });
            sca.execute();
        }
        if (position == channelList.size() - 1) {
            if (parentFragment != null && !loadingMoreChannels && !noMoreChannelFound) {
                loadingMoreChannels = true;
                parentFragment.loadMore();
            }
        }

        return convertView;
    }

    protected void parseDataAndStoreinDb(String data, ViewHolder finalHolder) {
        List<Videos> videosList = new ArrayList<>();

        try {
            JSONObject mainObj = new JSONObject(data);
            JSONObject dObj = mainObj.getJSONObject("d");
            JSONObject queryObj = dObj.getJSONObject("query");
            JSONObject primaryQueryObj = queryObj.getJSONObject("PrimaryQueryResult");
            JSONObject releventObj = primaryQueryObj.getJSONObject("RelevantResults");
            JSONObject tableObj = releventObj.getJSONObject("Table");
            JSONObject rowsObj = tableObj.getJSONObject("Rows");
            JSONArray resultArray = rowsObj.getJSONArray("results");
            for(int i = 0; i<resultArray.length();i++){
                Map<String ,String> videoFieldsMap=new HashMap<String, String>();
                JSONObject resultObj= resultArray.getJSONObject(i);
                JSONObject cellesObj= resultObj.getJSONObject("Cells");
                JSONArray resultInnerArray = cellesObj.getJSONArray("results");
                for(int j = 0; j<resultInnerArray.length();j++){
                    JSONObject obj= resultInnerArray.getJSONObject(j);
                    //System.out.println("obj ="+obj.getString("Key"));
                    videoFieldsMap.put(obj.getString("Key"), obj.getString("Value"));
                }
                videoFieldsMap.put("ListId", item.getId());
                Videos video = convertMapToVideoModel(videoFieldsMap);
                System.out.println("video convertedMap ="+video);
                videosList.add(video);
            }
            if(dbVideos == null ){
                dbVideos = new DBVideos(context);
            }
            dbVideos.insertVideos(videosList);
        //  mapVideos.put(item.getId(), videosList);
            setVideoListAdapter(videosList,finalHolder);
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
    private void setVideoListAdapter(List<Videos> list, ViewHolder finalHolder) {
        if(videoListAdapter == null){
            videoListAdapter = new VideoListAdapter(context, list,parentFragment);
        }
        videoListAdapter.setVideoList(list);
        System.out.println("list ="+list.size());
        System.out.println("list ="+list.get(1));
        finalHolder.videoListView.setAdapter(videoListAdapter);
        finalHolder.videoListView.setVisibility(View.VISIBLE);
        finalHolder.imgProcess.setVisibility(View.GONE);
        ListHeightUtils.setListViewHeightBasedOnChildren(finalHolder.videoListView);

    }

    private Videos convertMapToVideoModel(Map<String, String> videoFieldsMap){
        Class clazz=Videos.class;
        Object object = null;
        System.out.println("videoFieldsMap ="+videoFieldsMap);
        try{
            object=clazz.newInstance();
            for(Field field:clazz.getDeclaredFields()){
                field.setAccessible(true);
                System.out.println("field =="+videoFieldsMap.get(field));
                field.set(object, videoFieldsMap.get(field.getName()));
            }
            System.out.println("object ="+object.toString());
        }catch(Exception e){
            e.printStackTrace();
        }
        return (Videos)object;
    }

    }

Answer 1

Adapter 定义了在 View 中显示项目列表的规则 - 它通常在 ListView 或 RecyclerView 的上下文中(但实际上可以是很多东西)。 View 不知道底层数据集何时更改，因此在其初始绘制后，需要告知其数据何时不再是最新的。

假设您有以下列表:

[A, B, C]

在某个时候，用户点击 API 并更新列表:

[A, B, C, D, E, F]

显示这个列表的ListView仍然只会显示:

[A, B, C]

当您在附加到 ListView 的适配器上调用 notifyDataSetChanged() 时，它将更新 ListView 以显示完整的新数据集:

[A, B, C, D, E, F]

根据您使用的适配器类型，也可以通知整个数据集已更改，或者执行更具体的更新调用，例如 RecyclerView 的 notifyItemChanged、notifyItemRemoved , notifyItemMoved 等