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您好，我的应用程序有问题，当我运行它时它停止了。它让我明白了：

    09-19 11:15:42.941: W/dalvikvm(6202): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
09-19 11:15:43.083: E/AndroidRuntime(6202): FATAL EXCEPTION: main
09-19 11:15:43.083: E/AndroidRuntime(6202): java.lang.RuntimeException: Unable to start activity ComponentInfo{cz.bakalari.bakalari/cz.bakalari.bakalari.ParseActivity}: java.lang.NullPointerException
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.os.Looper.loop(Looper.java:137)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread.main(ActivityThread.java:5041)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at java.lang.reflect.Method.invokeNative(Native Method)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at java.lang.reflect.Method.invoke(Method.java:511)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at dalvik.system.NativeStart.main(Native Method)
09-19 11:15:43.083: E/AndroidRuntime(6202): Caused by: java.lang.NullPointerException
09-19 11:15:43.083: E/AndroidRuntime(6202):     at cz.bakalari.bakalari.XML_Parser.getValue(XML_Parser.java:112)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at cz.bakalari.bakalari.ParseActivity.onCreate(ParseActivity.java:45)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.Activity.performCreate(Activity.java:5104)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
09-19 11:15:43.083: E/AndroidRuntime(6202):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
09-19 11:15:43.083: E/AndroidRuntime(6202):     ... 11 more

这是我的活动：

public class ParseActivity extends Activity {



    static final String KEY_XML = "xml";

    static final String KEY_VERZE = "verze";
    static final String KEY_BKTYP = "bktyp";
    static final String KEY_STATUS = "status";
    static final String KEY_UTYP = "utyp";


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

        XML_Parser parser = new XML_Parser();
        String xml = "<xml><verze>1.0</verze><bktyp>LOGIN</bktyp><status>OK</status><utyp>R</utyp></xml>";

        Document doc = parser.getDomElement(xml);

        NodeList nl = doc.getElementsByTagName(KEY_XML);
        Element e = (Element) nl.item(1);



        TextView parseview1 = (TextView) findViewById(R.id.parseview1);
        TextView parseview2 = (TextView) findViewById(R.id.parseview2);
        TextView parseview3 = (TextView) findViewById(R.id.parseview3);

        parseview1.setText(parser.getValue(e,KEY_VERZE));
        parseview2.setText(parser.getValue(e,KEY_BKTYP));
        parseview3.setText(parser.getValue(e,KEY_STATUS));



        };
    }

这是我的 XML_Parser.class：

public class XML_Parser {

    // constructor
    public XML_Parser() {

    }

    /**
     * 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));
        }
}

你能看出这个问题吗？我是android dev的新手，所以我需要一些简单的答案。

4

1 回答 1

0

NodeList.item 返回 NodeList 中第索引位置的节点，如果该索引不是有效索引，则返回 null。

你的xml只有一个元素“xml”，

NodeList nl = doc.getElementsByTagName(KEY_XML);

并且年节点列表大小为 1。

尝试更换

Element e = (Element) nl.item(1);

到

Element e = (Element) nl.item(0);
于 2013-09-25T21:12:41.383 回答