使XML解析器在没有连接的情况下不会崩溃

Question

我有一个xml解析器类，如果我没有连接到互联网，它会崩溃。无论如何，我可以让班级去布局说，＆＃34;没有连接＆＃34;或者当连接不存在时类似的东西。感谢

Xml Parser

public class XMLParser {

// constructor
public XMLParser() {

}

/**
 * Getting XML from URL making HTTP request
 * @param url string
 * */
public String getXmlFromUrl(String url) {
    String xml = null;

    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    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));
}
}

使用解析器的活动

public class CustomizedListView extends Fragment {  // All static variables
    static final String URL = "http://graffiti.hostoi.com/00Graffiti00/lists/00main00.xml";
    // XML node keys
    static final String KEY_SONG = "song"; // parent node
    static final String KEY_ID = "id";
    static final String KEY_ARTIST = "artist";
    static final String KEY_DURATION = "duration";
    static final String KEY_THUMB_URL = "thumb_url";
    static final String KEY_LINK = "key";

    ListView list;
    LazyAdapter adapter;
    ArrayList<HashMap<String, String>> songsList;

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

    View rootView = inflater.inflate(R.layout.news, container, false);



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

    list=(ListView)  rootView.findViewById(R.id.list);

    new RetrieveXML().execute(URL);
    XMLParser parser = new XMLParser();


    // Getting adapter by passing xml data ArrayList



    // Click event for single list row
    list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {

            Intent intent = new Intent(getActivity(), Article.class);
            new Bundle();
            intent.putExtra( "b", songsList.get(position).get(KEY_LINK));
            startActivity(intent);



        }

    });
    return rootView;
}

class RetrieveXML extends AsyncTask<String, Void, String> {

    private Exception exception;
    XMLParser parser = new XMLParser();


    protected String doInBackground(String... urls) {
        try {

            return parser.getXmlFromUrl(urls[0]);
        } catch (Exception e) {
            this.exception = e;
            return null;
        }
    }

    protected void onPostExecute(String xml) {
        Document doc = parser.getDomElement(xml); // getting DOM element

        NodeList nl = doc.getElementsByTagName(KEY_SONG);
        // looping through all song nodes <song>
        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_LINK, parser.getValue(e, KEY_LINK));
            map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
            map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
            map.put(KEY_THUMB_URL, parser.getValue(e, KEY_ID));
            map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));

            // adding HashList to ArrayList
            songsList.add(map);

        }

        adapter=new LazyAdapter(getActivity(), songsList);

        list.setAdapter(adapter);
    }
}

Answer 1

试试这个..

在包中添加以下类

<强> Utils.java

import android.content.Context;
import android.net.ConnectivityManager;
import android.util.Log;

public class Utils {

    public static boolean connectivity(Context c) {

        if(c != null)
        {
            ConnectivityManager connec = (ConnectivityManager) c.getSystemService(Context.CONNECTIVITY_SERVICE);
            try {
                android.net.NetworkInfo wifi = connec.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

                android.net.NetworkInfo mobile = connec.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

                if (wifi.isConnected()||mobile.isConnected())
                    return true;
                else if (wifi.isConnected() && mobile.isConnected())
                    return true;
                else
                    return false;

            } catch (NullPointerException e) {
                Log.d("ConStatus", "No Active Connection");
                return false;
            }
        }
        else
        {
            Log.v("utils--", "null");
            return false;
        }
    }

}

在调用RetrieveXML AsyncTask 之前，请使用如下代码。

            if(Utils.connectivity(getActivity()))
            {
                new RetrieveXML().execute(URL);
                XMLParser parser = new XMLParser();
            }
            else
            {
                Toast.makeText(getActivity(), "Please connect to working internet connection.", Toast.LENGTH_SHORT).show();
            }