Android Node.getNodeValue在某些情況下返回NULL

Question

我想解析一個XML文件。這是文件：

<root> 
     <entry> 
       <username>achanda</username> 
       <latitude>45.123</latitude> 
       <longtitude>76.345</longtitude> 
       <timestamp>2000</timestamp> 
       <filename>image2.jpg</filename> 
     </entry> 
     <entry> 
       <username>achanda</username> 
       <latitude>45.123</latitude> 
       <longtitude>76.345</longtitude> 
       <timestamp>2000</timestamp> 
       <filename>image2.jpg</filename> 
     </entry> 
     <entry> 
       <username>achanda</username> 
       <latitude>45.123</latitude> 
       <longtitude>76.345</longtitude> 
       <timestamp>2000</timestamp> 
       <filename>image2.jpg</filename> 
     </entry> 
</root> 

這是代碼：

private String getTextValue(Element ele, String tagName) { 
     String textVal = ""; 
     NodeList nl = ele.getElementsByTagName(tagName); 
     if (nl != null && nl.getLength() > 0) { 
      Element el = (Element) nl.item(0); 
      Node n = el.getFirstChild(); 
      //TODO this line throws an exception for the last 
      //entry in the xml file. Fix this 
      textVal = n.getNodeValue(); 
     } 
     return textVal; 
    } 

這解析前兩個<entry>標籤，但getNodeValue()回報null最後標籤的文件。我發現here它應該在某些情況下返回null。那麼我如何提取字段呢？我試着將el.getFirstChild()轉換爲Element，即使這樣也行不通。

private float getFloatValue(Element ele, String tagName) { 
     return Float.parseFloat(getTextValue(ele, tagName)); 
    } 

    public ArrayList<GeoPoint> parseFile(String path) { 
     DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 
     Document dom = null; 
     ArrayList<GeoPoint> gp = new ArrayList<GeoPoint>(); 
     try { 
      DocumentBuilder db = dbf.newDocumentBuilder(); 
      dom = db.parse(path); 

      org.w3c.dom.Element eroot = dom.getDocumentElement(); 
      NodeList nl = eroot.getElementsByTagName("entry"); 

      if (nl != null && nl.getLength() > 0) { 
       for (int i = 0; i < nl.getLength(); i++) { 
        org.w3c.dom.Element el = (org.w3c.dom.Element) nl.item(i); 
        float lat = (float) (getFloatValue(el, LAT) * 1E6); 
        float lon = (float) (getFloatValue(el, LON) * 1E6); 
        Log.e("###LAT: ", Float.toString(lat)); 
        Log.e("###LON: ", Float.toString(lon)); 
        //gp.add(new GeoPoint((int) lat, (int) lon)); 
       } 
      } 
     } catch (ParserConfigurationException pce) { 
      pce.printStackTrace(); 
     } catch (SAXException se) { 
      se.printStackTrace(); 
     } catch (IOException ioe) { 
      ioe.printStackTrace(); 
     } 
     return gp; 
    } 

logcat的輸出：

12-08 01:05:38.718: D/AndroidRuntime(3148): Shutting down VM 
12-08 01:05:38.718: W/dalvikvm(3148): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
12-08 01:05:38.779: E/AndroidRuntime(3148): FATAL EXCEPTION: main 
12-08 01:05:38.779: E/AndroidRuntime(3148): java.lang.IllegalStateException: Could not execute method of the activity 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.view.View$1.onClick(View.java:2144) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.view.View.performClick(View.java:2485) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.view.View$PerformClick.run(View.java:9080) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.os.Handler.handleCallback(Handler.java:587) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.os.Handler.dispatchMessage(Handler.java:92) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.os.Looper.loop(Looper.java:130) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at java.lang.reflect.Method.invoke(Method.java:507) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at dalvik.system.NativeStart.main(Native Method) 
12-08 01:05:38.779: E/AndroidRuntime(3148): Caused by: java.lang.reflect.InvocationTargetException 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at java.lang.reflect.Method.invoke(Method.java:507) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at android.view.View$1.onClick(View.java:2139) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  ... 11 more 
12-08 01:05:38.779: E/AndroidRuntime(3148): Caused by: java.lang.NullPointerException 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.apps.terrapin.SearchActivity.getTextValue(SearchActivity.java:186) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.apps.terrapin.SearchActivity.getFloatValue(SearchActivity.java:192) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.apps.terrapin.SearchActivity.parseFile(SearchActivity.java:209) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.apps.terrapin.SearchActivity.searchData(SearchActivity.java:100) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  at com.apps.terrapin.SearchActivity.searchClicked(SearchActivity.java:70) 
12-08 01:05:38.779: E/AndroidRuntime(3148):  ... 14 more 

更新 一次我刪除XML文件的全部內容，並又寫了這個問題就解決了。看起來Android是以某種方式緩存文件的。這裏還有什麼問題呢？

Answer 1

一旦我刪除了xml文件的所有內容並重新寫入，此問題已得到解決。看起來Android是以某種方式緩存文件的。