如何在此項目中使用AsynTask

Question

AsyncTask 我是Android Developer的初學者。我想開發關於Map的應用程序。但我不知道如何應用AsyncTask。請建議我。對不起我的英語不好。 如何將AsyncTask應用於此文件？

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

您應該使用一個類，然後創建該類的實例，並調用它的執行方法：

例如：下面的定義

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

檢查鏈接PostTask：

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

Answer 2

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

要加載的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(); 


      } 

     }