Android 1.6代碼給出了2.3.3的空指針

Question

嗨我正在寫一個android應用程序。 我找到了用於xml解析的代碼片段。我在另一個項目上測試過，一切正常。所以我想讓我測試它在我的主要項目，但它給了我一個空指針：S。

這是我ParseXMLDemo類：

public class ParseXMLDemo extends ListActivity { 

@SuppressWarnings("rawtypes") 
private ArrayList vraag; 
@SuppressWarnings("rawtypes") 
private ArrayList a1; 
private ArrayList p1; 
private ArrayList a2; 
private ArrayList p2; 
private ArrayList a3; 
private ArrayList p3; 

@SuppressWarnings("unchecked") 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 


    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>(); 

    String xml = ParseXMLMethods.getXML(); 
    Document doc = ParseXMLMethods.XMLfromString(xml); 

    int numResults = ParseXMLMethods.numResults(doc); 

    if((numResults <= 0)){ 
     Toast.makeText(ParseXMLDemo.this, "Er is een fout opgetreden bij het updaten van de vragen. Probeert u het later opnieuw.", Toast.LENGTH_LONG).show(); 
     finish(); 
    } 

    NodeList children = doc.getElementsByTagName("os"); 

    for (int i = 0; i < children.getLength(); i++) { 

     HashMap<String, String> map = new HashMap<String, String>();  
     Element e = (Element)children.item(i); 
     vraag.add(ParseXMLMethods.getValue(e, "vraag")); 
     a1.add(ParseXMLMethods.getValue(e, "a1")); 
     p1.add(ParseXMLMethods.getValue(e, "p1")); 
     a2.add(ParseXMLMethods.getValue(e, "a2")); 
     p2.add(ParseXMLMethods.getValue(e, "p2")); 
     a3.add(ParseXMLMethods.getValue(e, "a3")); 
     p3.add(ParseXMLMethods.getValue(e, "p3")); 
     Toast.makeText(ParseXMLDemo.this, (CharSequence) vraag.get(i)+" "+a1.get(i)+" "+p1.get(i)+" "+a2.get(i)+" "+p2.get(i)+" "+a3.get(i)+" "+p3.get(i), Toast.LENGTH_LONG).show(); 

     map.put("id", ParseXMLMethods.getValue(e, "id")); 
     map.put("vraag", ParseXMLMethods.getValue(e, "vraag")); 
     map.put("a1", ParseXMLMethods.getValue(e, "a1")); 
     map.put("p1", ParseXMLMethods.getValue(e, "p2")); 
     map.put("a2", ParseXMLMethods.getValue(e, "a2")); 
     map.put("p2", ParseXMLMethods.getValue(e, "p2")); 
     map.put("a3", ParseXMLMethods.getValue(e, "a3")); 
     map.put("p3", ParseXMLMethods.getValue(e, "p3")); 

     mylist.add(map);    
    }  

    Toast.makeText(ParseXMLDemo.this, "testje"+mylist.get(1), Toast.LENGTH_LONG).show(); 

    ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.list_layout, 
        new String[] { "vraag", "a1", "p1", "a2", "p2", "a3", "p3" }, 
        new int[] { R.id.title, R.id.subtitle, R.id.sub1, R.id.sub11, R.id.sub2, R.id.sub22, R.id.sub3}); 

    setListAdapter(adapter); 

    final ListView lv = getListView(); 
    lv.setOnItemClickListener(new OnItemClickListener() { 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) {    
      @SuppressWarnings("unchecked") 
      HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);     
      Toast.makeText(ParseXMLDemo.this,o.get("vraag"), Toast.LENGTH_LONG).show(); 
     } 
    }); 
}} 

，這是我ParseXMLMethods類：

public class ParseXMLMethods { 

public final static Document XMLfromString(String xml){ 

    Document doc = null; 

    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 
    try { 

     DocumentBuilder db = dbf.newDocumentBuilder(); 

     InputSource is = new InputSource(); 
     is.setCharacterStream(new StringReader(xml)); 
     doc = db.parse(is); 

    } catch (ParserConfigurationException e) { 
     System.out.println("XML parse error: " + e.getMessage()); 
     return null; 
    } catch (SAXException e) { 
     System.out.println("Wrong XML file structure: " + e.getMessage()); 
     return null; 
    } catch (IOException e) { 
     System.out.println("I/O exeption: " + e.getMessage()); 
     return null; 
    } 
    return doc; 
} 

public final static String getElementValue(Node elem) { 
    Node kid; 
    if(elem != null){ 
     if (elem.hasChildNodes()){ 
      for(kid = elem.getFirstChild(); kid != null; kid = kid.getNextSibling()){ 
       if(kid.getNodeType() == Node.TEXT_NODE ){ 
        return kid.getNodeValue(); 
       } 
      } 
     } 
    } 
    return ""; 
} 

public static String getXML(){ 
     String line = null; 

     try { 

      DefaultHttpClient httpClient = new DefaultHttpClient(); 
      HttpPost httpPost = new HttpPost("http://www.oudersvragen.nl/test.xml"); 

      HttpResponse httpResponse = httpClient.execute(httpPost); 
      HttpEntity httpEntity = httpResponse.getEntity(); 
      line = EntityUtils.toString(httpEntity); 

     } catch (Exception e) { 
      line = "Internet Connection Error >> " + e.getMessage(); 
     } 
     return line; 
} 

public static int numResults(Document doc){  
    Node results = doc.getDocumentElement(); 
    int res = -1; 
    try{ 
     res = Integer.valueOf(results.getAttributes().getNamedItem("count").getNodeValue()); 
    }catch(Exception e){ 
     res = -1; 
    } 
    return res; 
} 

public static String getValue(Element item, String str) {  
    NodeList n = item.getElementsByTagName(str);   
    return ParseXMLMethods.getElementValue(n.item(0)); 
} 

}

有人能告訴我爲什麼它給了我一個空指針異常在Android 2.3.3項目以及爲什麼一切都按照它在android 1.6項目中應用的方式工作？ （FYI我運行在相同的Android 4.0的虛擬機項目）

logcat的輸出：

05-05 20:50:33.561: E/AndroidRuntime(3705): FATAL EXCEPTION: main 
05-05 20:50:33.561: E/AndroidRuntime(3705): java.lang.RuntimeException: Unable to start  activity ComponentInfo{com.hgs.database/com.hgs.database.ParseXMLDemo}:  java.lang.NullPointerException 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread.access$600(ActivityThread.java:123) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.os.Looper.loop(Looper.java:137) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at java.lang.reflect.Method.invoke(Method.java:511) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at dalvik.system.NativeStart.main(Native Method) 
05-05 20:50:33.561: E/AndroidRuntime(3705): Caused by: java.lang.NullPointerException 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at com.hgs.database.ParseXMLDemo.onCreate(ParseXMLDemo.java:57) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.Activity.performCreate(Activity.java:4465) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
05-05 20:50:33.561: E/AndroidRuntime(3705):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 

Answer 1

我才意識到，你提出了一個完整的程序（不包括佈局），所以我跑了。這裏是我的發現：

當我忘了，包括互聯網的權限，我發現打電話finish()不退出的onCreate（）。所以我加了返回指令：

if(numResults <= 0){ 
    Toast.makeText(Example.this, "Er is een fout opgetreden bij het updaten van de vragen. Probeert u het later opnieuw.", Toast.LENGTH_LONG).show(); 
    finish(); 
    return; 
} 

包括互聯網許可後，我注意到，你沒有初始化數組，因此：

@SuppressWarnings("rawtypes") 
private ArrayList vraag = new ArrayList(); 
@SuppressWarnings("rawtypes") 
private ArrayList a1 = new ArrayList(); 
private ArrayList p1 = new ArrayList(); 
private ArrayList a2 = new ArrayList(); 
private ArrayList p2 = new ArrayList(); 
private ArrayList a3 = new ArrayList(); 
private ArrayList p3 = new ArrayList(); 

現在它運行在我的2.3.3模擬器。