Question

当我试图获取listview的日期时，我得到了这个错误，当我搜索它时，我发现它的解决方案是使用异步任务，但不知道如何使用它，所以我怎么能在我的代码中使用它？

这是代码：

package com.example.ms;

import java.util.ArrayList;
import java.util.HashMap;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import com.example.ms.XMLParser;
import com.example.ms.LazyAdapter;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.AdapterView.OnItemClickListener;

public class PhotosActivity extends Activity {

    ListView list;
    LazyAdapter adapter;
    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";
    static final String URL = "http://api.androidhive.info/music/music.xml";

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_photos);

        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.photoslist);

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


        // Click event for single list row
        list.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {


            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.photos, menu);
        return true;
    }

}

Answer 1

是的，您必须运行解析代码，尤其是您执行http调用解析的调用.getXmlFromUrl（URL）;在一个分离的线程中。即在AsyncTask中。因此，将代码复制到AsyncTask.doInBackground（）并从doInbackground（）返回解析后的List。在AsyncTask.onPostExecution（List）中，您将收到已解析的列表，这就是设置ListView适配器的正确点，simce此方法将在主UI线程上执行。

公共类PhotosActivity扩展了Activity {

private XmlParserTask task;

public void onCreate(Bundle saved){
     super.onCreate(Bundle saved);
    // Do your UI setup
    task = new XmlParserTask();
    task.execute(URL);
 }


public void onDestroy(){
    super.onDestroy();
    // Avoid Memory leaks and android view not attached to window manager Exceptions
    if (task != null)
        task.cancel(true);
 }


private class XmlParserTask extends AsyncTask<String, Void, List<YouSongType>> {

     public List<YourSongType> doInBackground(String ... params){

         String url = params[0];

         List<YourSongType> resultList = new ArrayList<YourSongType>();

        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);

       // Add your xml parsed data in the list
       resultList.add();

       return resultList;
    }


   public void onPostExecution(List<YourSongType> songsList){
      adapter=new LazyAdapter(this, songsList);        
      list.setAdapter(adapter);
    }


}

Answer 2

您收到此错误是因为您尝试从网络中获取数据，而您在主线程上执行此操作！

`String xml = parser.getXmlFromUrl(URL);`

正如你所说的，你需要触发任何类型的线程以避免在mainthread上进行长时间处理，其中一个选项是AsyncTask，使用AsyncTask是直截了当的，基本上你有三种方法onPreExecute() doInBackground()和onPostExecute()

onPreExecute()和onPostExecute()在UI线程上运行，您可以使用它们来显示对话框，结果或从xml数据中提供列表

doInBackground()在netowrk线程上运行，所以你实现了从服务器获取xml，你可以使用onPostExcute()使用委托从doInBackground()的结果中更新你的列表

android.os.NetworkOnMainThreadException。需要使用异步任务来解决这个问题吗？

2 个答案: