使用AsyncTask解析XML

Question

我想從特定的Url獲取貨幣，但AsyncTask給我的運行時錯誤：我無法找到我必須做的事情。

public class MainActivity extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    WebServisXML xmlRead = new WebServisXML(this); 
    xmlRead.execute("http://www.tcmb.gov.tr/kurlar/today.xml"); 
} 

public class WebServisXML extends AsyncTask<String, String, List<String>> { 

    private Context context; 
    private ListView listView; 
    private ProgressDialog dialogBar; 
    List<String> dovizListe = new ArrayList<String>(); 
    HttpURLConnection baglanti = null; 

    public WebServisXML(Context context) { 
     this.context = context; 
     listView = (ListView) ((AppCompatActivity) context).findViewById(R.id.listView);} 
     protected void onPreExecute() { 
     super.onPreExecute(); 
     dialogBar = ProgressDialog.show(context, "Lütfen bekleyiniz...", "İşlem yükleniyor...", true); 
    } 

    @Override 
    protected List<String> doInBackground(String... params) { 
     try { 
      URL adressOfLink = new URL(params[0]); 
      baglanti = (HttpURLConnection) adressOfLink.openConnection(); 
      int responceCode = baglanti.getResponseCode(); 
      if (responceCode == HttpURLConnection.HTTP_OK) { 

       BufferedInputStream stream = new BufferedInputStream(baglanti.getInputStream()); 
       publishProgress("Döviz kurları okunuyor..."); 
       DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance(); 
       DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder(); 

       Document document = documentBuilder.parse(stream); 

       NodeList dovizNodeList = document.getElementsByTagName("Currency"); 

       for (int i = 0; i < dovizNodeList.getLength(); i++) { 

        Element element = (Element) dovizNodeList.item(i); 

        NodeList nodeBirim = element.getElementsByTagName("Unit"); 
        NodeList nodeIsim = element.getElementsByTagName("Isim"); 
        NodeList nodeAlis = element.getElementsByTagName("ForexBuying"); 
        NodeList nodeSatis = element.getElementsByTagName("ForexSelling"); 

        String birim = nodeBirim.item(0).getFirstChild().getNodeValue(); 
        String isim = nodeIsim.item(0).getFirstChild().getNodeValue(); 
        String alis = nodeAlis.item(0).getFirstChild().getNodeValue(); 
        String satis = nodeSatis.item(0).getFirstChild().getNodeValue(); 

        dovizListe.add(birim + " " + isim + " Alış:" + alis + " Satış:" + satis); 
       } 
       publishProgress("Liste güncelleniyor..."); 
      } 
     } catch (MalformedURLException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } catch (ParserConfigurationException e) { 
      e.printStackTrace(); 
     } catch (SAXException e) { 
      e.printStackTrace(); 
     }finally { 
      if(baglanti!=null) 
       baglanti.disconnect(); 
     } 
     return dovizListe; 
    } 

    @Override 
    protected void onProgressUpdate(String... values) { 
     super.onProgressUpdate(values); 
     dialogBar.setMessage(values[0]); 
    } 

    @Override 
    protected void onPostExecute(List<String> strings) { 
     super.onPostExecute(strings); 
     ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(context,android.R.layout.simple_expandable_list_item_1,strings); 
     listView.setAdapter(arrayAdapter); 
     dialogBar.cancel(); 
    } 
}} 

這是我的錯誤畫面：

Answer 1

其中一個節點的第一個孩子的是null的。 （節點沒有孩子）

沒有正確的行號我不能告訴你哪一個。 （MainActivity.java的98號線）

我建議增加一個檢查：

String birim = nodeBirim.item(0).getLength() > 0 ? nodeBirim.item(0).getFirstChild().getNodeValue() : ""; 
String isim = nodeIsim.item(0).getLength() > 0 ? nodeIsim.item(0).getFirstChild().getNodeValue() : ""; 
String alis = nodeAlis.item(0).getLength() > 0 ? nodeAlis.item(0).getFirstChild().getNodeValue() : ""; 
String satis = nodeSatis.item(0).getLength() > 0 ? nodeSatis.item(0).getFirstChild().getNodeValue() : "";