java - android xml节点解析数组适配器很奇怪

Question

我有一个奇怪的问题，(请先查看底部的较短版本)

当我的 Activity 第一次启动时， ListView 显示数据集正常。该适配器是一个自定义适配器，它显示 2 行文本和一个图像。我在 ListView 的单击事件上调用异步任务，数据集根据 ListView 中单击的内容进行更新 - 更具体地说，与适配器关联的数组被某些 xml 的解析重写，然后 notifyachapterdatasetchanged 方法是在 onPostExecute 函数中调用以更新 ListView 。但是，当我遍历某些 xml(格式非常好且经过验证)时，我总是得到 NullPointerException。还值得一提的是，解析所需值的算法很好，因为如上所述，如果我只写入数组的 1 个元素，那么我不会得到错误，我只是得到最后一个节点值，因此它在正确的位置循环.即，如果我简单地尝试将循环期间正在解析的当前节点值复制到 producyTypes[0] 中，那么循环中的最后一个值实际上会进入 ListView ，因为它会不断覆盖数组的这个元素

这是我的代码。`

public class main extends Activity implements OnItemClickListener

{

String selectedType="";
ListView lview3;
ImageView iv;
ListViewCustomAdapter adapter;
String test = "";
List<String> ls;

String productTypes[] = {"Monitor","Components","Systems","Laptops","Flash / Usb Memory",
        "Networking","Cables","Peripherals","Sound and Vision", "Software"};

String productsIncluded[] = {"Sizes (inches) 17, 19, 20",
        "Motherboards, PSU, Cases, Fans/Heatsinks/Coolers, Barebones Systems, Blue-Ray/DVD. Card Readers, Controller Cards, Drive Enclosures, Sound Cards",
        "Bundles, Switches and Hubs, Print Servers, Accessories/Modules",
        "Cables for: Drives, Networking, HDMI/Monitor, Audio/Video, USB/Firewire, Power, Miscellaneous",
        "Mice, Connectors, Bluetooth Devices",
        "Mp3/Mp4  Solar Panel",
        "Anti-Virus, Internet Security, Operating Systems, Office,,
        "",
        ""};

private static int images[] = {R.drawable.monitor, R.drawable.components, R.drawable.systems, 
    R.drawable.laptops, R.drawable.flashusb, R.drawable.networking, R.drawable.cables, R.drawable.
    peripherals, R.drawable.soundandvision, R.drawable.software};

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


    iv = (ImageView)findViewById(R.id.ImageView01);
    iv.setImageResource(R.drawable.logo);
    iv.setVisibility(View.VISIBLE);
    lview3 = (ListView) findViewById(R.id.listView3);
    adapter = new ListViewCustomAdapter(main.this, productTypes, productsIncluded, images);
    lview3.setAdapter(adapter);
    lview3.setOnItemClickListener(main.this);

}

@覆盖 public void onItemClick(AdapterView arg0, View arg1, int position, long id) {

     selectedType = "";                    

    if(position == 0)
    {
        selectedType= "Monitors";           
    }
    if(position == 1)
    {
        selectedType= "Hard Drives";            
    }
       Toast.makeText(this, Integer.toString(position), Toast.LENGTH_SHORT).show();      
       new async().execute();

    /*
    Intent intent = new Intent(getApplicationContext(),activitywo.class);
    Bundle bundle =new Bundle(); 
    bundle.putString("selectedType",selectedType);       
    intent.putExtras(bundle);              
    startActivity(intent);
    //Toast.makeText(this, "Title => "+productTypes[position]+" \n Description => "+productsIncluded[position], Toast.LENGTH_SHORT).show();      
    */
}
 private class async extends AsyncTask<String, Void, Void> {

     // UI Thread
     protected void onPreExecute() {

     }

     // automatically done on worker thread (separate from UI thread)
     protected Void doInBackground(final String... args) {

         try{

             Resources res = getResources();
             InputStream in;
             in = res.openRawResource(R.raw.core);

             DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
             DocumentBuilder builder = factory.newDocumentBuilder();
             Document dom = builder.parse(in);
             Element root = dom.getDocumentElement();
             NodeList items = root.getElementsByTagName("entry");


            count=0;
            for(int i =0;i<items.getLength();i++){
                Node item = items.item(i); 
                NodeList properties = item.getChildNodes();
                //productsDefinedByTypeArray = new String[properties.getLength()];


                for(int j = 0;j<properties.getLength();j++){
                    Node property = properties.item(j);
                    String name = property.getNodeName();

                    if(name.equalsIgnoreCase("g:product_type")){//everytime we hit g:product_type grab the value
                        String strText = property.getFirstChild().getNodeValue();

                        if(strText.contains(selectedType)){
                  //        
                            for(int k = 0;k<properties.getLength();k++){
                                Node propertysecond = properties.item(k);
                                String namesecond = propertysecond.getNodeName();
                                if(namesecond.equalsIgnoreCase("title")){//everytime we hit title grab the value
                                    String strTextsecond = propertysecond.getFirstChild().getNodeValue();
                                    productTypes[0] = strTextsecond;

                                    yo = strTextsecond;
                                    count++;
                                }                                    
                            }                                
                        }
                    }

                }


            }

当我试图将我从 xml 文件中解析出的“title”节点的值复制到 list-String- 时，代码崩溃了。我正在使用 list-string- 来表明即使您尝试将值复制到数组本身(与适配器关联的数组)，即使您注释掉 notifydatasetchanged () 行程序仍然会崩溃。 xml 格式正确且非常一致。我知道这是因为(尽管它真的很小而且我已经全部阅读了)!为什么我不能在循环进行时将每个节点值复制到我的数组/列表中？

非常感谢任何帮助。谢谢。

较短的版本:

我无法写入列表

 if(strText.contains(selectedType)){
                   //        
                             for(int k = 0;k<properties.getLength();k++){
                                 property = properties.item(k);
                                 name = property.getNodeName();
                                 if(name.equalsIgnoreCase("title")){//everytime we hit title grab the value
                                     String strTextsecond = property.getFirstChild().getNodeValue().toString();


                                     ls.add(strTextsecond.toString());

                                     //test = strTextsecond;

                                 }   

                             }         

                         }

Answer 1

也许你忘了初始化ls？我没有在您的代码中找到类似的内容:

ls = new List<String>();