Question

我花了两天时间试图找到解决此问题的方法，却无法在任何地方找到它。我的问题是：我有一个列表视图，其中每个项目有4个文本视图和一个ImageView。我正在使用Volley从网站上获取数据。数据正常加载，当我向下滚动时，一切都完美无缺。问题是当我向后滚动时。当我向后滚动时，图像和文本视图会出现0.5延迟（首先我看到最后一项的图片），然后显示内容。我已经使用viewholder尝试了recyclelerview和listview。两种解决方案都存在这种“轻弹”现象。

public class BigCategoryListViewAdapter extends BaseAdapter{

    private Context context;
    private String[] smallCatsList;
    private News news;
    private ImageLoader imageLoader;

    static class myViewHolder{
    TextView smallCatName;
    RelativeLayout spinner;
    ImageView newsImageView;
    TextView newsTitle;
    TextView newsContent;


}

public BigCategoryListViewAdapter(Context context, String[] smallCatsList){
    this.context = context;
    this.smallCatsList = smallCatsList;
    this.imageLoader = ImageLoader.getInstance();
    if(!this.imageLoader.isInited()) {  this.imageLoader.init(ImageLoaderConfiguration.createDefault(context));}
}

@Override
public int getCount() {
    return smallCatsList.length;
}

@Override
public Object getItem(int position) {
    return smallCatsList[position];
}

@Override
public long getItemId(int position) {return 0;} //modificar aqui



@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    final myViewHolder mvh;
    LayoutInflater inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);



    convertView = inflater.inflate(R.layout.bigcat_listview,null);

    mvh = new myViewHolder();

    mvh.smallCatName = (TextView) convertView.findViewById(R.id.bigcat_viewpager_smallcat);
    mvh.spinner = (RelativeLayout) convertView.findViewById(R.id.spinner);
    mvh.newsImageView = (ImageView) convertView.findViewById(R.id.bigcat_viewpager_imageView);
    mvh.newsTitle = (TextView) convertView.findViewById(R.id.bigcat_viewpager_news_title);
    mvh.newsContent = (TextView) convertView.findViewById(R.id.bigcat_viewpager_content);
    convertView.setTag(mvh);


    mvh.smallCatName.setText(smallCatsList[position]);

    JSONObject params = new JSONObject();
    try{
        params.put("slug",smallCatsList[position]);
        params.put("startIndex", 0);
        params.put("endIndex", 0);
    }catch (Exception e) {
        Log.e(getClass().toString(), "Error setting params for communication with server");
        e.printStackTrace();
    }

    Volley volley = Volley.getVolley(context);
    volley.runRequest(Request.Method.POST, VolleyConstants.PROD_URL + VolleyConstants.NEWS_FETCH_ROUTE,
        params, new Response.Listener<JSONObject>() {
        //---------------------Volley------------------//

    @Override
        public void onResponse(JSONObject response) {
            JSONArray responseArr = null;
            try {
                responseArr = response.getJSONArray("newsArr");
            } catch (Exception e) {
                e.printStackTrace();
            }

            for (int i = 0; i < responseArr.length(); i++) {
                try {
                    JSONObject object = responseArr.getJSONObject(i);
                    String photoURLString = object.getString("photo");
                    String titleString = object.getString("title");
                    String publisherString = object.getString("publisher");
                    String dateString = object.getJSONObject("date").getString("date");
                    String contentString = object.getString("contents");
                    String urlString = object.getString("url");

                    news = new News(photoURLString, titleString, publisherString, dateString, contentString,urlString);
                } catch (Exception e) {
                    news = new News("Unknown", "Unknown", "Unknown", "Unknown", "Unknown","Unknown");
                }




            }
            //tv2.setText(news.getNewsDate());

            mvh.newsContent.setText(news.getNewsContent());
            mvh.newsTitle.setText(news.getNewsHead());

            //---------------------Image Loading------------------//
            try {
                URL url = new URL(news.getNewsPic());
                imageLoader.loadImage(news.getNewsPic(), new ImageLoadingListener() {
                @Override
                    public void onLoadingStarted(String imageUri, View view) {

                    }

                @Override
                    public void onLoadingFailed(String imageUri, View view, FailReason failReason) {

                    }

                @Override
                    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
                        mvh.newsImageView.setImageBitmap(loadedImage);
                        mvh.spinner.setVisibility(View.GONE);
                    }

                @Override
                    public void onLoadingCancelled(String imageUri, View view) {


                    }
                });
            }catch(Exception e){
                mvh.newsImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.nopic));
                mvh.spinner.setVisibility(View.GONE);

            }


        }
    }, new CustomErrorListener("ERROR"));

    return convertView;
}

这是我的适配器。我的问题是，是否有办法消除此延迟以显示内容？或者是我的网络或列表视图本身的问题？我只想加载所有内容一次，然后用户可以上下滚动，而不必每次都刷新内容。

Answer 1

您每次调用getView时都会加载内容，这就是为什么它会像这样加载的原因。将Volley请求与getView分开，它应该完全在适配器之外，而不是在每个列表的每个负载上调用。你有你的新闻对象，你可以将一个ArrayList传递给适配器并从那里填充它，这将解决你的加载问题。此外，您在主线程而不是新线程中调用volley，您应该将两者分开，并在完成正在加载的内容时填充ListView适配器。

Answer 2

其一，ViewHolder模式示例应该是这样的：

if (convertView == null) {
    convertView = inflater.inflate(R.layout.bigcat_listview,null);

    mvh = new myViewHolder();
    //... rest of your code
} else {
    mvh = (myViewHolder) convertView.getTag();
    //... rest of your code
}

其次，主要的Volley加载东西不应该在适配器中，而是事先在别处处理然后传入。这个example应该可以帮到你很多。

具有复杂项目的Listview在加载时具有微秒延迟

2 个答案: