我每次都会遇到同样的错误。我现在已经工作了大约4个小时。 它用于RSS提要。
错误可能很简单，但我是初学者，所以请耐心等待。
我尝试添加StringBuffer，这是我开始收到错误的地方。如果我删除了StringBuffer，那么该应用仍会继续有效，但我更愿意使用它。
public class MainActivity extends Activity {
// A reference to the local object
private MainActivity local;
/**
* This method creates main application view
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set view
setContentView(R.layout.activity_main);
// Set reference to this activity
local = this;
GetRSSDataTask task = new GetRSSDataTask();
// Start download RSS task
task.execute("http://cantstophiphop.com/feed/");
// Debug the thread name
Log.d("RssReader", Thread.currentThread().getName());
}
private class GetRSSDataTask extends AsyncTask<String, Void, List<RssItem> > {
@Override
protected List<RssItem> doInBackground(String... urls) {
// Debug the task thread name
Log.d("RssReader", Thread.currentThread().getName());
try {
// Create RSS reader
RssReader rssReader = new RssReader(urls[0]);
// Parse RSS, get items
} catch (Exception e) {
Log.e(" RssReader", e.getMessage());
}
return null;
}
@Override
protected void onPostExecute(List<RssItem> result) {
// Get a ListView from main view
ListView itcItems = (ListView) findViewById(R.id.listView1);
// Create a list adapter
ArrayAdapter<RssItem> adapter = new ArrayAdapter<RssItem> (local,android.R.layout.simple_list_item_1, result);
// Set list adapter for the ListView
itcItems.setAdapter(adapter);
// Set list view item click listener
itcItems.setOnItemClickListener(new ListListener(result, local));
}
}
}
public class RssParseHandler extends DefaultHandler {
// List of items parsed
private List<RssItem> rssItems;
// We have a local reference to an object which is constructed while parser is working on an item tag
// Used to reference item while parsing
private RssItem currentItem;
// We have two indicators which are used to differentiate whether a tag title or link is being processed by the parser
// Parsing title indicator
private boolean parsingTitle;
// Parsing link indicator
private boolean parsingLink;
//private rssTitle;
private StringBuffer rssTitle;
public RssParseHandler() {
rssItems = new ArrayList();
}
// We have an access method which returns a list of items that are read from the RSS feed. This method will be called when parsing is done.
public List<RssItem> getItems() {
return rssItems;
}
// The StartElement method creates an empty RssItem object when an item start tag is being processed. When a title or link tag are being processed appropriate indicators are set to true.
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
if ("item".equals(qName)) {
currentItem = new RssItem();
} else if ("title".equals(qName)) {
parsingTitle = true;
rssTitle = new StringBuffer(); //Add this line *****************************
} else if ("link".equals(qName)) {
parsingLink = true;
}
}
// The EndElement method adds the current RssItem to the list when a closing item tag is processed. It sets appropriate indicators to false - when title and link closing tags are processed
@Override
public void endElement(String uri, String localName, String qName) throws SAXException{
if ("item".equals(qName)) {
rssItems.add(currentItem);
currentItem = null;
} else if ("title".equals(qName)) {
parsingTitle = false;
currentItem.setTitle(rssTitle.toString()); //Add this line *****************
} else if ("link".equals(qName)) {
parsingLink = false;
}
}
// Characters method fills current RssItem object with data when title and link tag content is being processed
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
if (parsingTitle) {
if (currentItem != null)
rssTitle.append(new String(ch, start, length)); //add This line ***************
} else if (parsingLink) {
if (currentItem != null) {
currentItem.setLink(new String(ch, start, length));
parsingLink = false;
}
}
}
}
12-30 19:03:20.792: E/AndroidRuntime(13573): FATAL EXCEPTION: main
12-30 19:03:20.792: E/AndroidRuntime(13573): java.lang.NullPointerException
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.widget.ListView.setAdapter(ListView.java:480)
12-30 19:03:20.792: E/AndroidRuntime(13573): at com.dailyloudrss.MainActivity$GetRSSDataTask.onPostExecute(MainActivity.java:78)
12-30 19:03:20.792: E/AndroidRuntime(13573): at com.dailyloudrss.MainActivity$GetRSSDataTask.onPostExecute(MainActivity.java:1)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.os.AsyncTask.finish(AsyncTask.java:632)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.os.Handler.dispatchMessage(Handler.java:102)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.os.Looper.loop(Looper.java:136)
12-30 19:03:20.792: E/AndroidRuntime(13573): at android.app.ActivityThread.main(ActivityThread.java:5017)
12-30 19:03:20.792: E/AndroidRuntime(13573): at java.lang.reflect.Method.invokeNative(Native Method)
12-30 19:03:20.792: E/AndroidRuntime(13573): at java.lang.reflect.Method.invoke(Method.java:515)
12-30 19:03:20.792: E/AndroidRuntime(13573): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-30 19:03:20.792: E/AndroidRuntime(13573): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-30 19:03:20.792: E/AndroidRuntime(13573): at dalvik.system.NativeStart.main(Native Method)