我正在尝试从以下 URL 解析 xml 数据： http: //cloud.tfl.gov.uk/TrackerNet/LineStatus但NullPointerException在线上显示：
NodeList nl = doc.getElementsByTagName(KEY_ITEM);
在我展示代码之前，我只想说一下发生了什么。首先，我将 XML 文件下载到 SDCard 中
saveToSdCard();
然后我用
getDataFromSDcard();
这是我的代码：主要活动：
public class DashboardFragment extends SherlockFragment {
private CardUI mCardView;
String TUBE_STATUS_URL;
String KEY_ITEM = "LineStatus";
String KEY_LINE = "Line";
String KEY_NAME = "name";
String KEY_STATUS_DETAILS = "StatusDetails";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
setHasOptionsMenu(true);
View rootView = inflater.inflate(R.layout.activity_dashboard,
container, false);
// Get the URL's
TUBE_STATUS_URL = "http://cloud.tfl.gov.uk/TrackerNet/LineStatus";
// Find the cards in inflated layout
CardUI cardGroup = (CardUI) rootView.findViewById(R.id.cardsview);
fillCards(cardGroup);
DownloadFeedsTask task = new DownloadFeedsTask();
task.execute(new String[] { "" });
return rootView;
}
private void fillCards(CardUI cardGroup) {
// Fill cards with data
// init CardView
mCardView = cardGroup;
mCardView.setSwipeable(true);
// create a stack
CardStack delayStack = new CardStack();
delayStack.setTitle("Tube Lines with delays");
// add cards to stack
delayStack.add(new MyCard("Jubilee Line", MyCard.LINE_UNAVAILABLE));
delayStack.add(new MyCard("Victoria Line", MyCard.LINE_AVAILABLE));
delayStack
.add(new MyCard("Piccadilly Line", MyCard.LINE_IN_MAINTENANCE));
delayStack.add(new MyCard("Northern", MyCard.LINE_AVAILABLE));
// create a stack
CardStack activeStack = new CardStack();
activeStack.setTitle("Active Tube Lines");
// add cards to stack
activeStack.add(new MyCard("Jubilee Line", MyCard.LINE_HIDE_STATUS));
activeStack.add(new MyCard("Victoria Line", MyCard.LINE_HIDE_STATUS));
// add stack to cardView
mCardView.addStack(delayStack);
mCardView.addStack(activeStack);
// draw cards
mCardView.refresh();
}
@Override
public boolean onOptionsItemSelected(
com.actionbarsherlock.view.MenuItem item) {
return super.onOptionsItemSelected(item);
}
private class DownloadFeedsTask extends AsyncTask<String, Void, String> {
ArrayList<HashMap<String, String>> menuItems;
@Override
protected String doInBackground(String... urls) {
try {
saveToSdCard();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
String response = "";
XMLParser parser = new XMLParser();
String xml = getDataFromSDcard(); // getting XML
Document doc = parser.getDomElement(xml); // getting DOM element
NodeList nl = doc.getElementsByTagName(KEY_ITEM);
// looping through all item nodes <item>
for (int i = 0; i < nl.getLength(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
// adding each child node to HashMap key => value
map.put(KEY_NAME, e.getAttribute(KEY_NAME));
// adding HashList to ArrayList
menuItems.add(map);
}
// Adding menuItems to ListView
// adapter = new SimpleAdapter(
// mCtx,
// menuItems,
// R.layout.list_item,
// new String[] { KEY_ADVERT, KEY_CONTACT, KEY_DATE },
// new int[] { R.id.textView1, R.id.textView2, R.id.textView3 });
return response;
}
private String getDataFromSDcard() {
// Get data from SDCard
// Find the directory for the SD Card using the API
// *Don't* hardcode "/sdcard"
File sdcard = Environment.getExternalStorageDirectory();
// Get the text file
File file = new File(sdcard, "Folder/test.xml");
// Read text from file
StringBuilder text = new StringBuilder();
try {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
text.append(line);
text.append('\n');
}
} catch (IOException e) {
// You'll need to add proper error handling here
}
return text.toString();
}
private void saveToSdCard() throws IOException {
try {
URL url = new URL(TUBE_STATUS_URL);
URLConnection conexion = url.openConnection();
conexion.connect();
int lenghtOfFile = conexion.getContentLength();
InputStream is = url.openStream();
File testDirectory = new File(
Environment.getExternalStorageDirectory() + "/Folder");
if (!testDirectory.exists()) {
testDirectory.mkdir();
}
FileOutputStream fos = new FileOutputStream(testDirectory
+ "/test.xml");
byte data[] = new byte[1024];
int count = 0;
long total = 0;
int progress = 0;
while ((count = is.read(data)) != -1) {
total += count;
int progress_temp = (int) total * 100 / lenghtOfFile;
if (progress_temp % 10 == 0 && progress != progress_temp) {
progress = progress_temp;
}
fos.write(data, 0, count);
}
is.close();
fos.close();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
protected void onPostExecute(String result) {
// Toast.makeText(getActivity(), String.valueOf(menuItems.size()),
// Toast.LENGTH_LONG).show();
// Log.d("Commuter+", String.valueOf(menuItems.size()));
}
}
}
还有我的 XMLParser 类：
public class XMLParser {
public String getXmlFromUrl(String url) {
String xml = null;
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
xml = EntityUtils.toString(httpEntity);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
// return XML
return xml;
}
public Document getDomElement(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) {
Log.e("Error: ", e.getMessage());
return null;
} catch (SAXException e) {
Log.e("Error: ", e.getMessage());
return null;
} catch (IOException e) {
Log.e("Error: ", e.getMessage());
return null;
}
Log.d("Commuter+", String.valueOf(doc.toString().length()));
// return DOM
return doc;
}
public String getValue(Element item, String str) {
NodeList n = item.getElementsByTagName(str);
return this.getElementValue(n.item(0));
}
public final String getElementValue( Node elem ) {
Node child;
if( elem != null){
if (elem.hasChildNodes()){
for( child = elem.getFirstChild(); child != null; child = child.getNextSibling() ){
if( child.getNodeType() == Node.TEXT_NODE ){
return child.getNodeValue();
}
}
}
}
return "";
}
}
我尝试通过使用具有 XML 数据的其他 URL 测试我的代码并且它可以工作来解决此问题，但是当我使用此 URL 时似乎存在问题。