Android XML 解析器捕获异常

Question

有人可以检查一下代码吗？我的 XMLParser 捕获了一个异常。我正在尝试将选项卡 fragment 与 ListView 一起使用，并使用 XML 解析器来解析远程数据库的结果。

MainActivity.java

public class MainActivity extends SherlockFragmentActivity implements TabListener {
    private Fragment mFragment;

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

        setContentView(R.layout.main);

        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionBar.setDisplayShowTitleEnabled(true);

        //mFragment = new AppleFragment();

        Tab tab = actionBar.newTab()
                .setText("Apple")
                .setTabListener(this)
                .setIcon(R.drawable.apple);

        actionBar.addTab(tab);


    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
         if (mFragment == null) {
                mFragment = new AppleFragment();
                ft.add(android.R.id.content, mFragment);
            } else {
                ft.attach(mFragment);
            }
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.detach(mFragment);
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }
}

AppleFragment.java

public class AppleFragment extends SherlockListFragment{


        static final String URL = "http://api.androidhive.info/pizza/?format=xml";
        // XML node keys
        static final String KEY_ITEM = "item"; // parent node
        static final String KEY_ID = "id";
        static final String KEY_NAME = "name";
        static final String KEY_COST = "cost";
        static final String KEY_DESC = "description";



        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){

        return super.onCreateView(inflater, container, savedInstanceState);

        }


        public void onActivityCreated(Bundle savedInstanceState) {

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


            XMLParser parser = new XMLParser();
            String xml = parser.getXmlFromUrl(URL); // 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_ID, parser.getValue(e, KEY_ID));
                map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
                map.put(KEY_COST, "Rs." + parser.getValue(e, KEY_COST));
                map.put(KEY_DESC, parser.getValue(e, KEY_DESC));

                // adding HashList to ArrayList
                menuItems.add(map);
            }

            ListAdapter adapter = new SimpleAdapter(getActivity(), menuItems,
                    R.layout.list_item,
                    new String[] { KEY_NAME, KEY_DESC, KEY_COST }, new int[] {
                            R.id.name, R.id.desciption, R.id.cost });


            setListAdapter(adapter);    


        }
}

XMLParser.java

public class XMLParser {

    // constructor
    public XMLParser() {

    }

    /**
     * Getting XML from URL making HTTP request
     * @param url string
     * */
    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;
    }

    /**
     * Getting XML DOM element
     * @param XML string
     * */
    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;
            }

            return doc;
    }

    /** Getting node value
      * @param elem element
      */
     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 "";
     }

     /**
      * Getting node value
      * @param Element node
      * @param key string
      * */
     public String getValue(Element item, String str) {     
            NodeList n = item.getElementsByTagName(str);        
            return this.getElementValue(n.item(0));
        }
}

日志:

10-05 16:36:50.453: E/AndroidRuntime(20162): FATAL EXCEPTION: main
10-05 16:36:50.453: E/AndroidRuntime(20162): java.lang.RuntimeException: Unable to start activity ComponentInfo{in.wptrafficanalyzer.actionbarsherlocknavtab/in.wptrafficanalyzer.actionbarsherlocknavtab.MainActivity}: android.os.NetworkOnMainThreadException
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.os.Looper.loop(Looper.java:137)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread.main(ActivityThread.java:4512)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at java.lang.reflect.Method.invokeNative(Native Method)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at java.lang.reflect.Method.invoke(Method.java:511)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:982)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at dalvik.system.NativeStart.main(Native Method)
10-05 16:36:50.453: E/AndroidRuntime(20162): Caused by: android.os.NetworkOnMainThreadException
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at java.net.InetAddress.getAllByName(InetAddress.java:220)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at in.wptrafficanalyzer.actionbarsherlocknavtab.XMLParser.getXmlFromUrl(XMLParser.java:45)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at in.wptrafficanalyzer.actionbarsherlocknavtab.AppleFragment.onCreateView(AppleFragment.java:38)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:870)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:505)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1136)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.Activity.performStart(Activity.java:4475)
10-05 16:36:50.453: E/AndroidRuntime(20162):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1943)
10-05 16:36:50.453: E/AndroidRuntime(20162):    ... 11 more

Answer 1

您正在主线程上运行网络操作。使用异步任务在后台线程中运行网络操作(在后台线程中进行 xml 解析)。这就是为什么您会收到 android.os.NetworkOnMainThreadException。

在异步任务中解析它，如下所示:

class XMLParsingTask extends AsyncTask<String, Void, RSSFeed> {


    protected void onPreExecute() {
    //show a progress dialog to the user or something
    }

    protected void doInBackground(String... urls) {
        //Parse your XML here
    }

    protected void onPostExecute() {
        //do something with your parsed xml here and dismiss the progress dialog
    }
 }

 new RXMLParsingTask().execute(null);

如果您不知道如何使用异步任务，这里有一些教程:

http://mobileorchard.com/android-app-developmentthreading-part-2-async-tasks/

http://www.vogella.com/articles/AndroidPerformance/article.html

这里是官方文档:https://developer.android.com/reference/android/os/AsyncTask.html