目前我面临以下问题-我创建了一个自定义ListView (1 x ImageView + 2 x TextView)。它显示来自I-net的内容，这是一个XML文件。
我在做什么-我使用AsyncTask在后台运行下载XML内容的过程，并通过调用publishProgress(…)方法为每个列表项从doInBackground(…)方法填充ListView。当doInBackground(…)完成时，我已经收集了我想要显示的每个图像的URL，然后从onPostExecute(…)方法开始图像的下载过程并为每个下载的图像更新UI。对我来说，问题是ListView应该在开始下载可绘制文件和更新列表之前填充至少几个项目。当前ListView显示一个单独的项目，当填充下一个，所有的图像已经下载。我调试应用程序，我看到一个我停在onPostExecute(…)方法，并希望采取ListView项目的数量，它只返回一个，因为它显示。
是否有一种方法来强制外观Listview的项目，在开始下载之前，这是因为我有I-net连接，是足够的，没有延迟下载图像。
我只忘了提一下，每个图像都不大于10KB。
这是我的自定义AsyncTask:private class DownloadFilesTask extends AsyncTask<String, Object, List<RSSItem>> {
protected void onPreExecute() {
super.onPreExecute();
la.clear();
}
protected List<RSSItem> doInBackground(String... urls) {
parse(urls[0]);
if (feed == null) { return null; }
rssList = feed.getAllItems();
Iterator<RSSItem> iterator = rssList.iterator();
while(iterator.hasNext()) {
if (isCancelled()) return null;
RSSItem rss = iterator.next();
publishProgress(rss);
}
return rssList;
}
protected void onProgressUpdate(Object... progress) {
super.onProgressUpdate(progress);
la.add((RSSItem)progress[0]);
la.notifyDataSetChanged();
}
protected void onPostExecute(List<RSSItem> result) {
super.onPostExecute(result);
Drawable downloadedImage;
for (int z = 0; z < rssList.size(); z++) {
downloadedImage = downloadImage(rssList.get(z).getImageURL());
((RSSItem)rssList.get(z)).setImage(downloadedImage);
la.notifyDataSetChanged();
}
}
protected void onCancelled() {
super.onCancelled();
}
}
private class ListAdapter extends ArrayAdapter<RSSItem> {
private List<RSSItem> items;
public ListAdapter(Context context, int textViewResourceId, List<RSSItem> items) {
super(context, textViewResourceId, items);
this.items = items;
}
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
if (v == null) {
LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vi.inflate(R.layout.list_item, null);
}
RSSItem item = items.get(position);
if (item != null) {
ImageView itemImage = (ImageView) v.findViewById(R.id.ivImage);
TextView title = (TextView) v.findViewById(R.id.tvTitle);
TextView description = (TextView) v.findViewById(R.id.tvDescription);
if (item.getImage() != null) {
itemImage.setBackgroundDrawable(item.getImage());
} else {
itemImage.setBackgroundDrawable(getResources().getDrawable(R.drawable.icon));
}
if (title != null) {
title.setText(item.getTitle());
}
if (description != null) {
description.setText(item.getDescription());
}
}
return v;
}
}
…和Item类:
public class RSSItem {
private String data = null;
private String description = null;
private Drawable image = null;
private String imageUrl = null;
private String title = null;
RSSItem() {
}
public void setData(String data) {
this.data = data;
}
public void setDescription(String description) {
this.description = description;
}
public void setImageURL(String imageURL) {
this.imageUrl = imageURL;
}
public void setImage(Drawable image) {
this.image = image;
}
public void setTitle(String title) {
this.title = title;
}
public String getData() {
return data;
}
public String getDescription() {
return description;
}
public Drawable getImage() {
return image;
}
public String getImageURL() {
return imageUrl;
}
public String getTitle() {
return title;
}
}
@MODIFICATIONS:
私有类DownloadFilesTask扩展AsyncTask> {onPreExecute() {
super.onPreExecute (); la.clear();
}
protected List<RSSItem> doInBackground(String... urls) {
parse(urls[0]);
if (feed == null) { return null; }
rssList = feed.getAllItems();
publishProgress(true);
Drawable downloadedImage;
for (int z = 0; z < rssList.size(); z++) {
downloadedImage = downloadImage(rssList.get(z).getImageURL());
((RSSItem)rssList.get(z)).setImage(downloadedImage);
}
return rssList;
}
protected void onProgressUpdate(Object... progress) {
super.onProgressUpdate(progress);
la.notifyDataSetChanged();
}
protected void onPostExecute(List<RSSItem> result) {
super.onPostExecute(result);
la.notifyDataSetChanged();
}
protected void onCancelled() {
super.onCancelled();
}
}
我不确定我理解你的问题，但我要做的是以下(如果我做对了):
我假设你有一个自定义对象你存储在你的ListView中，比如CustomItem。我将把URL Image的下载放在该对象的构造函数中，并将Drawable存储为CustomItem的成员。在您创建了新的CustomItem并获得了它的映像之后，publishProgress()并调用列表适配器上的notifyDataSetChanged()。
onPostExecute()方法中的代码移到doInBackground()方法的末尾。
试试这个:
private class DownloadFilesTask extends AsyncTask<String, RSSItem, Void> {
protected void onPreExecute() {
super.onPreExecute();
la.clear();
}
protected List<RSSItem> doInBackground(String... urls) {
parse(urls[0]);
if (feed == null) { return null; }
rssList = feed.getAllItems();
Iterator<RSSItem> iterator = rssList.iterator();
while(iterator.hasNext()) {
if (isCancelled()) return null;
RSSItem rss = iterator.next();
//this happens fast no need to do this
publishProgress(rss);
//la.add(rss);
}
Drawable downloadedImage;
for (int z = 0; z < rssList.size(); z++) {
downloadedImage = downloadImage(rssList.get(z).getImageURL());
((RSSItem)rssList.get(z)).setImage(downloadedImage);
publishProgress(null);
}
return rssList;
}
protected void onProgressUpdate(RSSItem... progress) {
super.onProgressUpdate(progress);
if progress!=null
la.add((RSSItem)progress[0]);
la.notifyDataSetChanged();
}
protected void onPostExecute(Void result) {
super.onPostExecute(result);
}
protected void onCancelled() {
super.onCancelled();
}
}
您是否在doInBackground()中填充列表适配器的底层数据集?然后，除了调用publishProgress()之外，您还需要在AsyncTask的onProgressUpdate()中调用adapter.notifyDataSetChanged()。