无法在进程的主线程上获取 XML DOM 解析数据

Question

我没有从代码中得到想要的输出。

我使用 XML DOM 解析从链接中获取标题、发布日期、描述和图像：http://autosportsindia.com/feed

通过编写的代码没有获得任何输出。即使 Logcat 显示正在从链接中获取数据。

请告诉我我的代码有什么问题。建议使用代码或链接解析 XML 的任何其他方法。

public class  MainActivity extends AppCompatActivity implements ResultsCallBack {

PlaceholderFragment taskFragment;
ListView articlesListView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (savedInstanceState == null) {
        taskFragment = new PlaceholderFragment();
        getSupportFragmentManager().beginTransaction().add(taskFragment, "MyFragment").commit();

    } else {
        taskFragment = (PlaceholderFragment) getSupportFragmentManager().findFragmentByTag("MyFragment");
    }
    taskFragment.startTask();

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

}

@Override
public void onPreExecute() {

}

@Override
public void onPostExecute(ArrayList<HashMap<String, String>> results) {

    articlesListView.setAdapter(new MyAdapter(this, results));
}

public static class PlaceholderFragment extends Fragment {

    AutoSportsIndia downloadTask;
    ResultsCallBack callBack;

    public PlaceholderFragment() {
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        callBack = (ResultsCallBack) activity;

        if(downloadTask!=null)
        {
            downloadTask.onAttach(callBack);
        }
    }


    @Override
    public void onActivityCreated(Bundle savedInstanceState) {

        super.onActivityCreated(savedInstanceState);
        setRetainInstance(true);
    }

    public void startTask() {
        if (downloadTask != null) {
            downloadTask.cancel(true);
        } else {
            downloadTask = new AutoSportsIndia(callBack);
            downloadTask.execute();
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        callBack = null;
        if(downloadTask!=null) {
            downloadTask.onDetach();
        }

    }
}


public static class AutoSportsIndia extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>> {

    ResultsCallBack callBack =null;

    public AutoSportsIndia(ResultsCallBack callBack) {
        this.callBack = callBack;

    }

    public void onAttach(ResultsCallBack callBack) {
        this.callBack = callBack;

    }

    public void onDetach() {
        callBack = null;

    }

    protected void onPreExecute() {
        if(callBack!=null)
        {
            callBack.onPreExecute();
        }

    }

    @Override
    protected ArrayList<HashMap<String, String>> doInBackground(Void... params) {

        String downloadURL = "http://autosportsindia.com/feed";
        ArrayList<HashMap<String, String>> results = new ArrayList<>();
        try {
            URL url = new URL(downloadURL);
            HttpURLConnection connection = (HttpURLConnection)url.openConnection();
            connection.setRequestMethod("GET");
            InputStream inputStream = connection.getInputStream();
            processXML(inputStream);
        } catch (Exception e) {
            L.m(e + "");
        }
        return results;
    }

    @Override
    protected void onPostExecute(ArrayList<HashMap<String, String>> result) {

        if(callBack!=null)
        {
            callBack.onPostExecute(result);
        }

    }

    public ArrayList<HashMap<String, String>> processXML(InputStream inputStream) throws Exception {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();

        Document xmlDocument = documentBuilder.parse(inputStream);
        Element rootElement = xmlDocument.getDocumentElement();
        L.m("" + rootElement.getTagName());
        NodeList itemsList = rootElement.getElementsByTagName("item");
        NodeList itemChildren = null;
        Node currentItem = null;
        Node currentChild = null;
        int count = 0;
        ArrayList<HashMap<String, String>> results = new ArrayList<>();
        HashMap<String, String> currentMap = null;

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

            currentItem = itemsList.item(i);
            itemChildren = currentItem.getChildNodes();

            currentMap = new HashMap<>();

            for (int j = 0; j < itemChildren.getLength(); j++) {
                currentChild = itemChildren.item(j);
                if (currentChild.getNodeName().equalsIgnoreCase("title")) {

                    currentMap.put("title", currentChild.getTextContent());
                   String temp="title: "+currentChild.getTextContent();
                   L.m(temp);
             }
             if (currentChild.getNodeName().equalsIgnoreCase("pubDate")) {

                   String temp1="pubDate: "+currentChild.getTextContent();
                 currentMap.put("pubDate", currentChild.getTextContent());
                   L.m(temp1);
             }

             if (currentChild.getNodeName().equalsIgnoreCase("description")) {

                 currentMap.put("description", currentChild.getTextContent());
                   String temp="description: "+currentChild.getTextContent();
                   L.m(temp);
             }
             if (currentChild.getNodeName().equalsIgnoreCase("media:thumbnail")) {
                    count++;
                    if (count == 2) {
                        L.m(currentChild.getAttributes().item(0).getTextContent());
                        currentMap.put("imageURL", currentChild.getAttributes().item(0).getTextContent());
                    }
                }

                if (currentMap != null && !currentMap.isEmpty()) {
                    results.add(currentMap);
                }
            }
            count = 0;
        }
        return results;
    }

}

}

interface ResultsCallBack {
    public void onPreExecute();

    public void onPostExecute(ArrayList<HashMap<String, String>> results);
}

class MyAdapter extends BaseAdapter {

ArrayList<HashMap<String, String>> dataSource = new ArrayList<>();
Context context;
LayoutInflater layoutInflater;

public MyAdapter(Context context, ArrayList<HashMap<String, String>> dataSource) {
    this.context = context;
    this.dataSource = dataSource;
    layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

}

@Override
public int getCount() {
    return dataSource.size();
}

@Override
public Object getItem(int position) {
    return dataSource.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View row = convertView;
    MyHolder holder = null;
    if(row == null)
    {
       row = layoutInflater.inflate(R.layout.custom_view, parent, false);
        holder = new MyHolder(row);
        row.setTag(holder);
    }
    else
    {
         holder = (MyHolder)row.getTag();
    }
    HashMap<String, String> currentItem = dataSource.get(position);
    holder.articleTitleText.setText(currentItem.get("title"));
    holder.articlePublishedDateText.setText(currentItem.get("pubDate"));
   // holder.articleImage.setImageURI(Uri.parse(currentItem.get("imageURL")));
    holder.articleDescriptionText.setText(currentItem.get("description"));

    return row;
}
}

class MyHolder {
    TextView articleTitleText;

    TextView articlePublishedDateText;

    ImageView articleImage;

TextView articleDescriptionText;

public MyHolder(View view) {

articleTitleText = (TextView) 

view.findViewById(R.id.articleTitleText);

articlePublishedDateText = (TextView) view.findViewById(R.id.articlePublishedDate);


    articleImage = (ImageView) view.findViewById(R.id.articleImage);

    articleDescriptionText = (TextView) view.findViewById(R.id.articleDescriptionText);
}

}

XML 页面：-

• activity_main.xml

  <ListView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/articlesListView"
      android:layout_alignParentTop="true"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true" />
  

• custom_view.xml

  <TextView
      android:id="@+id/articleTitleText"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_alignParentLeft="true"
      android:layout_alignParentRight="true"
      android:layout_alignParentTop="true"
      android:padding="12dp"
      android:text="Title"
      android:textAppearance="?android:attr/textAppearanceLarge"
      android:textColor="#444"/>
  
  <TextView
      android:id="@+id/articlePublishedDate"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignParentRight="true"
      android:layout_below="@+id/articleTitleText"
      android:paddingBottom="4dp"
      android:paddingLeft="12dp"
      android:paddingRight="12dp"
      android:paddingTop="4dp"
      android:text="Date"
      android:textAppearance="?android:attr/textAppearanceSmall"
      android:textColor="#444"/>
  
  <View
      android:id="@+id/separator1"
      android:layout_width="match_parent"
      android:layout_height="2dp"
      android:layout_below="@+id/articlePublishedDate"
      android:layout_marginLeft="12dp"
      android:layout_marginRight="12dp"
      android:background="#e67e22"/>
  
  <ImageView
      android:id="@+id/articleImage"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_below="@+id/separator1"
      android:scaleType="fitCenter"
      android:src="@drawable/ic_launcher"/>
  
  <TextView
      android:id="@+id/articleDescriptionText"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_below="@+id/articleImage"
      android:padding="12dp"
      android:text="Description"
      android:textColor="#444"/>
  

Answer 1

processXML 方法构建并返回一个ArrayList<HashMap<String, String>>。

在doInBackground方法中调用，但返回值被丢弃。 doInBackground 然后返回一个本地的results 对象，它是一个空列表。

如果您通过processXML 和doInBackground 方法进行了调试，您就会看到这一点。当我在评论中询问“您是否尝试过调试代码、单步调试并查看正在处理的值”时，您显然没有。