使用Http請求解析XML與AsyncTask

Question

我正在使用HTTP請求，解析一個XML連接到互聯網 一切工作正常，但我想要做的是從AsyncTask的新版本的android SDK的連接。 通常不應該給的問題，但我正在跟隨一個教程，並嘗試了很多選項，並在本網站上看到類似的線程後，我不能正確應用它。

這是我使用

活動1中的代碼：

public class CustomizedListView extends Activity { 
    // All static variables 
    static final String URL = "http://api.androidhive.info/music/music.xml"; 
    // XML node keys 
    static final String KEY_SONG = "song"; // parent node 
    static final String KEY_ID = "id"; 
    static final String KEY_TITLE = "title"; 
    static final String KEY_ARTIST = "artist"; 
    static final String KEY_DURATION = "duration"; 
    static final String KEY_THUMB_URL = "thumb_url"; 

    private ArrayList<HashMap<String, String>> data; 


    ListView list; 
    LazyAdapter adapter; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 


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

     XMLParser parser = new XMLParser(); 
     String xml = parser.getXmlFromUrl(URL); // getting XML from URL 
     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_TITLE, parser.getValue(e, KEY_TITLE)); 
      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_THUMB_URL)); 

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

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

     // Getting adapter by passing xml data ArrayList 
     adapter=new LazyAdapter(this, songsList);   
     list.setAdapter(adapter); 

    } 
} 

這是第二個活動：

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)); 
     } 
} 

...我明白，它必須被封裝在AsycTask中是：

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; 

...不過要使用兩個activitys的字符串，我無法找到一個方法來做到

非常感謝您的幫助

問候

Answer 1

使用這種類型的類的子類，如在您的活動：

private class YourDownload extends AsyncTask<Void, Void, Void> { 

     @Override 
     protected Void doInBackground(Void... params) { 
      /* 
         make connection & download XML here, 
         use your XML parser class object to parse the xml from here 

         create ArrayList & etc. from here... 

        */ 
      return null; 

     } 

     @Override 
     protected void onPostExecute(Void result) { 
      // postexecute logic 
      super.onPostExecute(result); 
     } 

     @Override 
     protected void onPreExecute() { 
      // pre execute logic 
      super.onPreExecute(); 
     } 

    } 

使用YourDownload從的onCreate（）爲new YourDownload().execute();

大概這可以幫到你..