Question

我正在尝试构建一个基本的RSS Feed。我没有在代码中显示错误，但是当我运行应用程序时，它崩溃并出现以下错误：

致命异常：AsyncTask＃1 java.lang.RuntimeException：执行doInBackground（）时发生错误

这是我的MainActivity.java代码：

public class MainActivity extends ListActivity {

List<String> headlines;
List<String>links;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //initialize variables
    headlines = new ArrayList<String>();
    links = new ArrayList<String>();

    new PostTask().execute();

    //binding data to list
    ArrayAdapter <String>adapter=  new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, headlines);
    setListAdapter(adapter);
}

private InputStream getInputStream(URL url) {
    try{
        return url.openConnection().getInputStream();
    }catch(IOException e){
        return null;
    }
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    Uri uri = Uri.parse(links.get(position));
    Intent intent = new Intent(Intent.ACTION_VIEW, uri);
    startActivity(intent);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

//ASYNCH CLASS
private class PostTask extends AsyncTask<String, Integer, String>{

    @Override
    protected String doInBackground(String... arg0) {
        try{
            //link to data source
            URL url = new URL("http://feeds.pcworld.com/pcworld/latestnews");

            //Set up parser
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            factory.setNamespaceAware(false);
            XmlPullParser xpp = factory.newPullParser();

            //get XML from input stream
            xpp.setInput(getInputStream(url), "UTF_8");

            //Keep track of which tag inside of XML
            boolean insideItem = false;

            //Loop through the XML file and extract data required
            int eventType = xpp.getEventType();
            while(eventType != XmlPullParser.END_DOCUMENT){
                if(xpp.getName().equalsIgnoreCase("item")){
                    insideItem = true;
                }else if(xpp.getName().equalsIgnoreCase("title")){
                    if(insideItem){
                        //Get title
                        headlines.add(xpp.nextText());
                    }
                }else if(xpp.getName().equalsIgnoreCase("link")){
                    if(insideItem){
                        //Get link
                        links.add(xpp.nextText());
                    }
                }else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){
                insideItem = false;
            }
            eventType = xpp.next();//move to next element
        }
    }catch(MalformedURLException e){
        e.printStackTrace();
    }catch(XmlPullParserException e){
        e.printStackTrace();
    }catch(IOException e){
        e.printStackTrace();
    }
        return null;
    }

    public void onPostExecute(URL url) {

    }

}

}

有人能指出我哪里出错了吗？非常感谢！

登录CAT错误：

01-11 17:27:50.061: E/AndroidRuntime(7746): FATAL EXCEPTION: AsyncTask #1
01-11 17:27:50.061: E/AndroidRuntime(7746): java.lang.RuntimeException: An error occured while executing doInBackground()
01-11 17:27:50.061: E/AndroidRuntime(7746):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.FutureTask.run(FutureTask.java:239)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.lang.Thread.run(Thread.java:856)
01-11 17:27:50.061: E/AndroidRuntime(7746): Caused by: java.lang.NullPointerException
01-11 17:27:50.061: E/AndroidRuntime(7746):     at com.example.simplerss.MainActivity$PostTask.doInBackground(MainActivity.java:89)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at com.example.simplerss.MainActivity$PostTask.doInBackground(MainActivity.java:1)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
01-11 17:27:50.061: E/AndroidRuntime(7746):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
01-11 17:27:50.061: E/AndroidRuntime(7746):     ... 4 more

Answer 1

我想当xpp.getClass()引用一组标记内的文本时xpp返回null。如果您查看XmlPullParser's documentation中的示例：

 while (eventType != XmlPullParser.END_DOCUMENT) {
  if(eventType == XmlPullParser.START_DOCUMENT) {
      System.out.println("Start document");
  } else if(eventType == XmlPullParser.START_TAG) {
      System.out.println("Start tag "+xpp.getName());
  } else if(eventType == XmlPullParser.END_TAG) {
      System.out.println("End tag "+xpp.getName());
  } else if(eventType == XmlPullParser.TEXT) {
      System.out.println("Text "+xpp.getText());
  }
  eventType = xpp.next();
 }

请注意，重点是eventType。如果你只想抓住"title"和 "link"代码，在START_TAG：

部分中添加这些检查

else if(eventType == XmlPullParser.START_TAG) {
    if(xpp.getName().equalsIgnoreCase("title")){
        //Get title
    }else if(xpp.getName().equalsIgnoreCase("link")){
        //Get link
    }
}

空指针错误RSS提要

1 个答案: