java如何正确下载多个图像（视频缩略图）

Question

我为kaltura媒体平台编写客户端。 我有一个活动“视频”。在此活动中，我必须显示带有缩略图的视频列表 首先，我使用kaltura api下载视频列表，效果很好。每个视频条目都有一个字段thumbnailUrl，它指向视频的缩略图。 当我为视频下载这个缩略图时，它（缩略图）的下载顺序不正确，有些缩略图没有下载，有些缩略图为其他视频重复，有些没有下载。 这是下载ind视频时的回调代码：

private void handleFetchvideoListTask(List<VideoObject> videoObjects){
        LinearLayout videoListProgressBarContainer = (LinearLayout)mActivity.findViewById(R.id.videoListProgressBarContainer);
        LinearLayout videoListViewContainer = (LinearLayout)mActivity.findViewById(R.id.videoListViewContainer);

        videoListProgressBarContainer.setVisibility(View.GONE);
        videoListViewContainer.setVisibility(View.VISIBLE);

        ListView listView = (ListView)videoListViewContainer.findViewById(R.id.videoListView);
        VideoListAdapter adapter = new VideoListAdapter((LayoutInflater) mActivity.getSystemService(Context.LAYOUT_INFLATER_SERVICE));
        adapter.setList(videoObjects);
        listView.setAdapter(adapter);
        DownloadThumbnailsTask task = new DownloadThumbnailsTask(videoObjects, adapter);
        task.execute();
    }

这是下载Thumbnailstask的代码：

public class DownloadThumbnailsTask extends AsyncTask<List<VideoObject>, VideoObject, Void>{

        private List<VideoObject> videoObjectList = null;
        private List<VideoObject> toProcess = null;
        private VideoListAdapter adapter = null;

        public DownloadThumbnailsTask(List<VideoObject> videoObjectList, VideoListAdapter adapter){
            this.videoObjectList = videoObjectList;
            this.toProcess = new ArrayList<VideoObject>(videoObjectList);
            this.adapter = adapter;
        }

        @Override
        protected Void doInBackground(List<VideoObject>... lists) {

            for(int i=0; i<toProcess.size(); i++){
                VideoObject item = videoObjectList.get(i);
                String urldisplay = item.getThumbnailUrl();
                Bitmap mIcon11 = null;
                try {
                    InputStream in = new java.net.URL(urldisplay).openStream();
                    mIcon11 = BitmapFactory.decodeStream(in);
                } catch (Exception e) {
                    Log.e("Error", e.getMessage());
                    e.printStackTrace();
                }
                item.setThumbnail(mIcon11);
                mIcon11 = null;
                publishProgress(item);
            }
            return null;
        }

        @Override
        protected void onProgressUpdate(VideoObject... values) {
            if(values != null && values.length > 0){
                VideoObject item = values[0];
                videoObjectList.remove(item);
                videoObjectList.add(item);
                adapter.setList(videoObjectList);
                adapter.notifyDataSetChanged();
            }
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            this.toProcess.clear();
            this.toProcess = null;
        }
    }

这是适配器的代码：

public class VideoListAdapter extends BaseAdapter {

    private List<VideoObject> list;
    private LayoutInflater layoutInflater;

    public VideoListAdapter(LayoutInflater layoutInflater){
        this.layoutInflater = layoutInflater;
    }

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

    @Override
    public Object getItem(int i) {
        return list.get(i);
    }

    @Override
    public long getItemId(int i) {
        return list.get(i).getId();
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        if(view == null){
            view = layoutInflater.inflate(R.layout.list_item_video, viewGroup, false);
        }
        ViewHolder viewHolder = new ViewHolder(view);
        view.setTag(viewHolder);
        VideoObject item = getVideoObjectItem(i);
        viewHolder.duration.setText(item.getFormattedDuration());
        viewHolder.title.setText(item.getName());
        if(item.getThumbnail() != null){
            viewHolder.thumbnail.setImageBitmap(item.getThumbnail());
        }
        return view;
    }

    private VideoObject getVideoObjectItem(int position){
        return (VideoObject) getItem(position);
    }

    public List<VideoObject> getList() {
        return list;
    }

    public void setList(List<VideoObject> list) {
        this.list = list;
    }

    public static class ViewHolder {
        public final ImageView thumbnail;
        public final TextView title;
        public final TextView duration;

        public ViewHolder(View view) {
            this.thumbnail = (ImageView)view.findViewById(R.id.imgVideoThumbnail);
            this.title = (TextView)view.findViewById(R.id.txtVideoName);
            this.duration = (TextView)view.findViewById(R.id.txtVideoDuration);
        }
    }
}

这是我代码的结果：

Answer 1

你的日志里有什么东西吗？可能打开流或解码失败。图像大吗

Answer 2

我注意到两件事：

1. 在doInBackground内您正在等待

   InputStream in = new java.net.URL(urldisplay).openStream(); mIcon11 = BitmapFactory.decodeStream(in);

在下载下一个图像之前完成

试试这个：

    protected Void doInBackground(List<VideoObject>... lists) {
        for(final int i=0; i<toProcess.size(); i++){
            try {
                new Thread(){
                    @Override
                    public void run() {
                        VideoObject item = videoObjectList.get(i);
                        String urldisplay = item.getThumbnailUrl();
                        Bitmap mIcon11 = null;
                        try {
                            InputStream in = new java.net.URL(urldisplay).openStream();
                            mIcon11 = BitmapFactory.decodeStream(in);
                        } catch (Exception e) {
                            Log.e("Error", e.getMessage());
                            e.printStackTrace();
                        }
                        item.setThumbnail(mIcon11);
                        publishProgress(item);
                    }
                }.start();
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
            }
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(VideoObject... values) {
        adapter.notifyDataSetChanged();
    }

我认为这两条线是问题所在：

    videoObjectList.remove(item);
    videoObjectList.add(item);

您正在删除一个项目，然后在底部再次添加。设置位图后只需调用notifyDataSetChanged

1. 在getView内，您每次都在创建一个新的ViewHolder

   @Override
   public View getView(int i, View view, ViewGroup viewGroup) {
       ViewHolder viewHolder;
       if(view == null){
           view = layoutInflater.inflate(R.layout.list_item_video, viewGroup, false);
           viewHolder = new ViewHolder(view);
           view.setTag(viewHolder);
       }else{
           viewHolder = view.getTag();
       }
       VideoObject item = getVideoObjectItem(i);
       viewHolder.duration.setText(item.getFormattedDuration());
       viewHolder.title.setText(item.getName());
       if(item.getThumbnail() != null){
           viewHolder.thumbnail.setImageBitmap(item.getThumbnail());
       }
       return view;
   }