我已经创建了一个RSS阅读器，如下面的教程所示： http://techiedreams.com/android-rss-reader-part-3-action-bar-with-animated-item/
我的问题是： 当我加载列表（使用ListActivity.java）时，我有时会得到一个NullPointerException，我只能看到一些列表项中的文本和其他一些列表中的图像。
logCat是：
04-07 22:01:26.900: W/System.err(22141): java.lang.NullPointerException
04-07 22:01:26.900: W/System.err(22141): at com.td.rssreader.parser.DOMParser.parseXml(DOMParser.java:56)
04-07 22:01:26.900: W/System.err(22141): at com.td.rssreader.ListActivity$2.run(ListActivity.java:115)
04-07 22:01:26.900: W/System.err(22141): at java.lang.Thread.run(Thread.java:856)
04-07 22:01:26.945: D/dalvikvm(22141): GC_CONCURRENT freed 887K, 10% free 13642K/15111K, paused 2ms+13ms, total 34ms
04-07 22:01:56.425: W/IInputConnectionWrapper(22141): getSelectedText on inactive InputConnection
04-07 22:01:56.425: W/IInputConnectionWrapper(22141): setComposingText on inactive InputConnection
04-07 22:01:56.425: W/IInputConnectionWrapper(22141): getExtractedText on inactive InputConnection
04-07 22:02:03.165: W/IInputConnectionWrapper(22141): showStatusIcon on inactive InputConnection
DOMParser类第56行是：
theString = nchild.item(j).getFirstChild().getNodeValue();
并且ListActivity行115是：
feed = tmpDOMParser.parseXml(feedLink);
为了让它发挥作用，我必须做些什么......？我真的找不到我的错误：（
编辑：
ListActivity.java
public class ListActivity extends Activity {
RSSFeed feed;
ListView lv;
CustomListAdapter adapter;
String feedLink;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.feed_list);
// set the feed link for refresh
feedLink = new SplashActivity().RSSFEEDURL;
// Get feed form the file
feed = (RSSFeed) getIntent().getExtras().get("feed");
// Initialize the variables:
lv = (ListView) findViewById(R.id.listView);
lv.setVerticalFadingEdgeEnabled(true);
// Set an Adapter to the ListView
adapter = new CustomListAdapter(this);
lv.setAdapter(adapter);
// Set on item click listener to the ListView
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// actions to be performed when a list item clicked
int pos = arg2;
Bundle bundle = new Bundle();
bundle.putSerializable("feed", feed);
Intent intent = new Intent(ListActivity.this,
DetailActivity.class);
intent.putExtras(bundle);
intent.putExtra("pos", pos);
startActivity(intent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
new MenuInflater(this).inflate(R.menu.activity_main, menu);
return (super.onCreateOptionsMenu(menu));
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.refresh_option:
refreshList(item);
return (true);
case R.id.about_option:
Toast.makeText(this, "RSS Reader!", Toast.LENGTH_SHORT).show();
return (true);
}
return super.onOptionsItemSelected(item);
}
public void refreshList(final MenuItem item) {
/* Attach a rotating ImageView to the refresh item as an ActionView */
LayoutInflater inflater = (LayoutInflater) getApplication()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
ImageView iv = (ImageView) inflater.inflate(R.layout.action_refresh,
null);
Animation rotation = AnimationUtils.loadAnimation(getApplication(),
R.anim.refresh_rotate);
rotation.setRepeatCount(Animation.INFINITE);
iv.startAnimation(rotation);
item.setActionView(iv);
// trigger feed refresh:
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
DOMParser tmpDOMParser = new DOMParser();
feed = tmpDOMParser.parseXml(feedLink);
ListActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
if (feed != null && feed.getItemCount() > 0) {
adapter.notifyDataSetChanged();
// lv.setAdapter(adapter);
item.getActionView().clearAnimation();
item.setActionView(null);
}
}
});
}
});
thread.start();
}
@Override
protected void onDestroy() {
super.onDestroy();
adapter.imageLoader.clearCache();
adapter.notifyDataSetChanged();
}
// List adapter class
class CustomListAdapter extends BaseAdapter {
private LayoutInflater layoutInflater;
public ImageLoader imageLoader;
public CustomListAdapter(ListActivity activity) {
layoutInflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader = new ImageLoader(activity.getApplicationContext());
}
@Override
public int getCount() {
// Set the total list item count
return feed.getItemCount();
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// Inflate the item layout and set the views
View listItem = convertView;
int pos = position;
if (listItem == null) {
listItem = layoutInflater.inflate(R.layout.list_item, null);
}
// Initialize the views in the layout
ImageView iv = (ImageView) listItem.findViewById(R.id.thumb);
TextView tvTitle = (TextView) listItem.findViewById(R.id.title);
TextView tvDate = (TextView) listItem.findViewById(R.id.date);
// Set the views in the layout
imageLoader.DisplayImage(feed.getItem(pos).getImage(), iv);
tvTitle.setText(feed.getItem(pos).getTitle());
tvDate.setText(feed.getItem(pos).getDate());
return listItem;
}
}
}
DOMParser.java
public class DOMParser {
private RSSFeed _feed = new RSSFeed();
public RSSFeed parseXml(String xml) {
// _feed.clearList();
URL url = null;
try {
url = new URL(xml);
} catch (MalformedURLException e1) {
e1.printStackTrace();
}
try {
// Create required instances
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
// Parse the xml
Document doc = db.parse(new InputSource(url.openStream()));
doc.getDocumentElement().normalize();
// Get all <item> tags.
NodeList nl = doc.getElementsByTagName("item");
int length = nl.getLength();
for (int i = 0; i < length; i++) {
Node currentNode = nl.item(i);
RSSItem _item = new RSSItem();
NodeList nchild = currentNode.getChildNodes();
int clength = nchild.getLength();
// Get the required elements from each Item
for (int j = 1; j < clength; j = j + 2) {
Node thisNode = nchild.item(j);
String theString = null;
String nodeName = thisNode.getNodeName();
theString = nchild.item(j).getFirstChild().getNodeValue();
if (theString != null) {
if ("title".equals(nodeName)) {
// Node name is equals to 'title' so set the Node
// value to the Title in the RSSItem.
_item.setTitle(theString);
}
else if ("description".equals(nodeName)) {
_item.setDescription(theString);
// Parse the html description to get the image url
String html = theString;
org.jsoup.nodes.Document docHtml = Jsoup
.parse(html);
Elements imgEle = docHtml.select("img");
_item.setImage(imgEle.attr("src"));
}
//description
else if ("pubDate".equals(nodeName)) {
// We replace the plus and zero's in the date with
// empty string
String formatedDate = theString.replace(" +0000",
"");
_item.setDate(formatedDate);
}
if ("link".equals(nodeName)) {
// Node name is equals to 'title' so set the Node
// value to the Title in the RSSItem.
_item.setLink(theString);
}
}
}
// add item to the list
_feed.addItem(_item);
}
} catch (Exception e) {
e.printStackTrace();
}
// Return the final feed once all the Items are added to the RSSFeed
// Object(_feed).
return _feed;
}
}
答案 0 :(得分：3)
所以你得到的是java.lang.NullPointerException：
theString = nchild.item(j).getFirstChild().getNodeValue();
问题是您没有null检查并且假设所有内容都是非null，因此该行中的其中一个调用返回null，然后您正在尝试在其上调用另一种方法。此外，您需要一些代码组织。这就是你拥有的......
for (int j = 1; j < clength; j = j + 2) {
Node thisNode = nchild.item(j);
String theString = null;
String nodeName = thisNode.getNodeName();
theString = nchild.item(j).getFirstChild().getNodeValue();
if (theString != null) {
// rest of your code
在尝试使用对象之前添加一些null检查，如下所示：
for (int j = 1; j < clength; j = j + 2) {
Node thisNode = nchild.item(j);
String theString = null;
if (thisNode != null && thisNode.getFirstChild() != null) {
theString = thisNode.getFirstChild().getNodeValue();
}
if (theString != null) {
String nodeName = thisNode.getNodeName();
// rest of your code
注意：这会修复您的直接NullPointerException，您可能会遇到其他错误，这可能无法解决所有问题（您的代码仍然相当具体），但这应该可以解决您的问题正在张贴。