Android - XML解析器應用程序

Question

我正在開發一個android應用程序，它使用SAX解析服務器中的XML文件並以列表的形式顯示。我收到空指針異常。但是，當我執行與java應用程序相同的代碼時，刪除所有android的東西，我可以打印列表中想要顯示的列表。這是大約700個項目的文件。 我無法從使用Logcat的日誌中瞭解太多。我是Android開發新手。如果你能幫助我，這真的很有幫助。

06-08 13:27:04.032: ERROR/AndroidRuntime(403): FATAL EXCEPTION: main 
06-08 13:27:04.032: ERROR/AndroidRuntime(403): java.lang.RuntimeException: Unable to start activity ComponentInfo{rss.com/rss.com.RSSReader}: java.lang.NullPointerException 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.os.Handler.dispatchMessage(Handler.java:99) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.os.Looper.loop(Looper.java:123) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread.main(ActivityThread.java:3647) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at java.lang.reflect.Method.invokeNative(Native Method) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at java.lang.reflect.Method.invoke(Method.java:507) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at dalvik.system.NativeStart.main(Native Method) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403): Caused by: java.lang.NullPointerException 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at rss.com.RSSReader.onCreate(RSSReader.java:33) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586) 
06-08 13:27:04.032: ERROR/AndroidRuntime(403):  ... 11 more 

我的清單文件

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="rss.com" 
    android:versionCode="1" 
    android:versionName="1.0"> 
<uses-sdk android:minSdkVersion="9" /> 

<application android:icon="@drawable/icon" android:label="@string/app_name"> 
    <activity android:name=".RSSReader" 
       android:label="@string/app_name"> 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 
      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity android:name=".ShowDescription" > 
    </activity> 
</application> 
</manifest> 

Java代碼：

public class RSSReader extends Activity implements OnItemClickListener{ 

    /** Called when the activity is first created. */ 
    public RSSFeed feed=null; 
    public List<RSSItem> list = null; 
    public final static String RSSFEEDOFCHOICE = "http://people.rit.edu/~vxr9024/chemicalFeed.xml"; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    feed = getFeed(RSSFEEDOFCHOICE); 
    list = feed.getAllItems(); 
    UpdateDisplay(list); 
} 

RSSFeed getFeed(String urlToRssFeed) 
{ 
    FeedParser parsedFeed = new FeedParser(); 
    try { 
     URL url = new URL(urlToRssFeed); 
     XMLReader xread = XMLReaderFactory.createXMLReader(); 
     xread.setContentHandler(parsedFeed); 
     InputSource is = new InputSource(url.openStream()); 
     xread.parse(is); 
     return parsedFeed.getFeed(); 
    } catch (SAXException e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
    return null; 
    } catch (FileNotFoundException e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
    return null; 
    } catch (IOException e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
    return null; 
    }catch (Exception e){ 
    System.out.println("Blahblah"); 
    return null; 
    } 
} 

private void UpdateDisplay(List<RSSItem> list) { 
    // TODO Auto-generated method stub 
    RSSItem[] items = new RSSItem[list.size()]; 
    list.toArray(items); 
    ListView itemlist = (ListView) findViewById(R.id.itemlist); 
    //RSSItem[] items = new RSSItem[()]; 
    ArrayAdapter<RSSItem> adapter = new ArrayAdapter<RSSItem>(this, android.R.layout.simple_list_item_1, 
      items); 
    itemlist.setAdapter(adapter); 
    itemlist.setOnItemClickListener(this); 
    itemlist.setSelection(0); 
} 

@Override 
public void onItemClick(AdapterView parent, View v, int position, long id) { 
    // TODO Auto-generated method stub 
    Intent intentItem = new Intent(this,ShowDescription.class); 
    Bundle b = new Bundle(); 
    b.putString("chemicalName",feed.getItem(position).getChemicalName()); 
    b.putString("synonyms",feed.getItem(position).getSynonyms()); 
    b.putString("formula",feed.getItem(position).getFormula()); 
    intentItem.putExtra("android.intent.extra.INTENT", b); 
    startActivity(intentItem); 
} 
} 

Answer 1

也許你需要

<uses-permission android:name="android.permission.INTERNET"/> 
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 

否則應用程序無法使用上網看你的RSS ？