Question

的AsyncTask 我是Android Developer的初学者。我想开发关于Map的应用程序。但我不知道如何应用AsyncTask。请建议我。对不起我的英语不好。如何为此文件应用AsyncTask？

import java.io.InputStream;
import java.util.ArrayList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import com.google.android.gms.maps.model.LatLng;

import android.content.Context;
import android.util.Log;

public class GMapV2Direction {
 public final static String MODE_DRIVING = "driving";
 public final static String MODE_WALKING = "walking";

 public GMapV2Direction() { }

 public Document getDocument(LatLng start, LatLng end, String mode) {
  String url = "http://maps.googleapis.com/maps/api/directions/xml?"
          + "origin=" + start.latitude + "," + start.longitude  
          + "&destination=" + end.latitude + "," + end.longitude 
          + "&sensor=false&units=metric&mode=driving";

        try {
            HttpClient httpClient = new DefaultHttpClient();
            HttpContext localContext = new BasicHttpContext();
            HttpPost httpPost = new HttpPost(url);
            HttpResponse response = httpClient.execute(httpPost, localContext);
            InputStream in = response.getEntity().getContent();
            DocumentBuilder builder = 
                    DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = builder.parse(in);
            return doc;
        } catch (Exception e) {
            e.printStackTrace();
        }
  return null;
 }

 public String getDurationText (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("duration");
        Node node1 = nl1.item(0);
        NodeList nl2 = node1.getChildNodes();
        Node node2 = nl2.item(getNodeIndex(nl2, "text"));
        Log.i("DurationText", node2.getTextContent());
  return node2.getTextContent();
 }

 public int getDurationValue (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("duration");
        Node node1 = nl1.item(0);
        NodeList nl2 = node1.getChildNodes();
        Node node2 = nl2.item(getNodeIndex(nl2, "value"));
        Log.i("DurationValue", node2.getTextContent());
  return Integer.parseInt(node2.getTextContent());
 }

 public String getDistanceText (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("distance");
        Node node1 = nl1.item(0);
        NodeList nl2 = node1.getChildNodes();
        Node node2 = nl2.item(getNodeIndex(nl2, "text"));
        Log.i("DistanceText", node2.getTextContent());
  return node2.getTextContent();
 }

 public int getDistanceValue (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("distance");
        Node node1 = nl1.item(0);
        NodeList nl2 = node1.getChildNodes();
        Node node2 = nl2.item(getNodeIndex(nl2, "value"));
        Log.i("DistanceValue", node2.getTextContent());
  return Integer.parseInt(node2.getTextContent());
 }

 public String getStartAddress (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("start_address");
        Node node1 = nl1.item(0);
        Log.i("StartAddress", node1.getTextContent());
  return node1.getTextContent();
 }

 public String getEndAddress (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("end_address");
        Node node1 = nl1.item(0);
        Log.i("StartAddress", node1.getTextContent());
  return node1.getTextContent();
 }

 public String getCopyRights (Document doc) {
  NodeList nl1 = doc.getElementsByTagName("copyrights");
        Node node1 = nl1.item(0);
        Log.i("CopyRights", node1.getTextContent());
  return node1.getTextContent();
 }

 public ArrayList getDirection (Document doc) {
  NodeList nl1, nl2, nl3;
        ArrayList listGeopoints = new ArrayList();
        nl1 = doc.getElementsByTagName("step");
        if (nl1.getLength() > 0) {
            for (int i = 0; i < nl1.getLength(); i++) {
                Node node1 = nl1.item(i);
                nl2 = node1.getChildNodes();

                Node locationNode = nl2.item(getNodeIndex(nl2, "start_location"));
                nl3 = locationNode.getChildNodes();
                Node latNode = nl3.item(getNodeIndex(nl3, "lat"));
                double lat = Double.parseDouble(latNode.getTextContent());
                Node lngNode = nl3.item(getNodeIndex(nl3, "lng"));
                double lng = Double.parseDouble(lngNode.getTextContent());
                listGeopoints.add(new LatLng(lat, lng));

                locationNode = nl2.item(getNodeIndex(nl2, "polyline"));
                nl3 = locationNode.getChildNodes();
                latNode = nl3.item(getNodeIndex(nl3, "points"));
                ArrayList arr = decodePoly(latNode.getTextContent());
                for(int j = 0 ; j < arr.size() ; j++) {
                 listGeopoints.add(new LatLng(arr.get(j).latitude
                                , arr.get(j).longitude));
                }

                locationNode = nl2.item(getNodeIndex(nl2, "end_location"));
                nl3 = locationNode.getChildNodes();
                latNode = nl3.item(getNodeIndex(nl3, "lat"));
                lat = Double.parseDouble(latNode.getTextContent());
                lngNode = nl3.item(getNodeIndex(nl3, "lng"));
                lng = Double.parseDouble(lngNode.getTextContent());
                listGeopoints.add(new LatLng(lat, lng));
            }
        }

        return listGeopoints;
 }

 private int getNodeIndex(NodeList nl, String nodename) {
  for(int i = 0 ; i < nl.getLength() ; i++) {
   if(nl.item(i).getNodeName().equals(nodename))
    return i;
  }
  return -1;
 }

 private ArrayList decodePoly(String encoded) {
  ArrayList poly = new ArrayList();
  int index = 0, len = encoded.length();
  int lat = 0, lng = 0;
  while (index < len) {
   int b, shift = 0, result = 0;
   do {
    b = encoded.charAt(index++) - 63;
    result |= (b & 0x1f) << shift;
    shift += 5;
   } while (b >= 0x20);
   int dlat = ((result & 1) != 0 
                                ? ~(result >> 1) : (result >> 1));
   lat += dlat;
   shift = 0;
   result = 0;
   do {
    b = encoded.charAt(index++) - 63;
    result |= (b & 0x1f) << shift;
    shift += 5;
   } while (b >= 0x20);
   int dlng = ((result & 1) != 0 
                                ? ~(result >> 1) : (result >> 1));
   lng += dlng;

   LatLng position = 
                                new LatLng((double)lat / 1E5, (double)lng / 1E5);
   poly.add(position);
  }
  return poly;
 }
}

Answer 1

你应该为它使用一个类，然后创建一个类的实例并调用它的执行方法：

例如：

new PostTask().execute("http://feeds.pcworld.com/pcworld/latestnews");

检查下面的链接，了解 PostTask 的定义：

http://androidresearch.wordpress.com/2012/03/17/understanding-asynctask-once-and-forever/

Answer 2

http://developer.android.com/reference/android/os/AsyncTask.html

加载AsyncTask

        new TheTask().execute(); // load it on ui thread

的AsyncTask

      class TheTask extends AsyncTask<Void,Void,Void>
      {
          @Override  
          public void doInBackground(void... params)
          {
             // all your network related operation here
             // do not update ui here 
             getDocument(start,end,mode);
             return null; 
          } 

      }

Answer 3

public class MyFirstMethod extends AsyncTask<String, Void, Document> {
            ProgressDialog dialog;

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                dialog = new ProgressDialog(context);
                dialog.setMessage("Loading....");
                dialog.show();
            }

            @Override
            protected Document doInBackground(String... params) {
                String url = params[0];
                try {
                    HttpClient httpClient = new DefaultHttpClient();
        HttpContext localContext = new BasicHttpContext();
        HttpPost httpPost = new HttpPost(url);
        HttpResponse response = httpClient.execute(httpPost, localContext);
        InputStream in = response.getEntity().getContent();
        DocumentBuilder builder = 
                DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document doc = builder.parse(in);


                } catch (Exception e) {
                    e.printStackTrace();
                }

                return doc;
            }

            @Override
            protected void onPostExecute(Document result) {

                super.onPostExecute(result);
                dialog.dismiss();
                dialog.cancel();


            }

        }

如何在此项目中使用AsyncTask

3 个答案: