Parsing XML with XPath

Question

I'm writing a simple Android app to display XML content in a ListView using XPath. My code is given under. It's catching null exception. Please help me around :( I've tried Google and different tutorials but none of them seem to solve my problem :(

public class MainActivity extends ListActivity {

ArrayList<String> mPeople = new ArrayList<String>();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    try {
        parseData();
    } catch(Exception ex) {
        Toast.makeText(this, "Exception: " + ex.getMessage(), Toast.LENGTH_LONG).show();
        System.out.println(ex.getMessage() +"==============");

    }

    // pass adapter w/ data queried through XPath to ListView
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mPeople);
    setListAdapter(adapter);
}

private void parseData() throws Exception {    
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();

Document doc = db.parse(new URL("http://www.w3schools.com/xpath/books.xml").openStream());
// query XPath instance, this is the parser
XPath xpath = XPathFactory.newInstance().newXPath();
// specify the xpath expression
// String expression = " /bookstore/book/title ";

XPathExpression e = xpath.compile("/bookstore/book/title");

// list of nodes queried
NodeList nodes = (NodeList)e.evaluate(doc, XPathConstants.NODESET);

Toast.makeText(this, "count: " + String.valueOf(nodes.getLength()),Toast.LENGTH_SHORT).show();
// if node found
if(nodes != null && nodes.getLength() > 0) {
  mPeople.clear();
  int len = nodes.getLength();
  for(int i = 0; i < len; ++i) {
      // query value
      Node node = nodes.item(i);
      mPeople.add(node.getTextContent());
  }
}
}
}

What output I get is a Toast containg Exception: null. I think openStream() in db.parse() is returning null . If anyone finds a solution, please let me know, it would be highly appreciated. Thanks.

EDIT: Here's the Logcat

06-01 10:25:42.586: I/System.out(1401): null==============
06-01 10:25:45.721: I/Choreographer(1401): Skipped 210 frames!  The application may be doing too much work on its main thread.
06-01 10:25:47.226: I/Choreographer(1401): Skipped 1768 frames!  The application may be doing too much work on its main thread.
06-01 10:25:47.467: D/gralloc_goldfish(1401): Emulator without GPU emulation detected.

Answer 1

try to do and call asynctask.execute from activity oncreate.it may solve your problem. 执行并从活动oncreate调用asynctask.execute。它可能会解决您的问题。 U got error this- just because of ur doing network call on main thread as it may require time more than 6 sec as application may treat as "ANR" by OS. 仅仅是因为您在主线程上进行网络调用，因为它可能需要6秒钟以上的时间，因为应用程序可能会将其视为“ ANR”。