在android sdk中的两个位置之间的地图中绘制线条时出现问题

package com.hands;

import java.net.HttpURLConnection;
import java.net.URL;

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

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

import android.os.Bundle;
import android.util.Log;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;

public class DrawlineActivity extends MapActivity {
     MapView myMapView = null;
     MapController myMC = null;
     GeoPoint geoPoint = null;
     @Override
     public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      setContentView(R.layout.main);
      myMapView = (MapView) findViewById(R.id.mapview);

      geoPoint = null;
      myMapView.setSatellite(false);
      double fromLat = 12.303534;
      double fromLong = 76.64611;
      double toLat = 12.9715987;
      double toLong = 77.5945627;

      String sourceLat = Double.toString(fromLat);
      String sourceLong = Double.toString(fromLong);
      String destinationLat = Double.toString(toLat);
      String destinationLong = Double.toString(toLong);

  String pairs[] = getDirectionData(sourceLat,sourceLong, destinationLat, destinationLong );
//The above line pairs[] retrieving null value. Showing as NULL POINTER EXCEPTION
      String[] lngLat = pairs[0].split(",");

      // STARTING POINT
      GeoPoint startGP = new GeoPoint((int) (Double.parseDouble(lngLat[1]) * 1E6), (int) (Double.parseDouble(lngLat[0]) * 1E6));

      myMC = myMapView.getController();
      geoPoint = startGP;
      myMC.setCenter(geoPoint);
      myMC.setZoom(10);
      myMapView.getOverlays().add(new DirectionPathOverlay(startGP, startGP));

      // NAVIGATE THE PATH

      GeoPoint gp1;
      GeoPoint gp2 = startGP;

      for (int i = 1; i < pairs.length; i++) {
       lngLat = pairs[i].split(",");
       gp1 = gp2;
       // watch out! For GeoPoint, first:latitude, second:longitude

       gp2 = new GeoPoint((int) (Double.parseDouble(lngLat[1]) * 1E6),(int) (Double.parseDouble(lngLat[0]) * 1E6));
       myMapView.getOverlays().add(new DirectionPathOverlay(gp1, gp2));
       Log.d("xxx", "pair:" + pairs[i]);
      }

      // END POINT
      myMapView.getOverlays().add(new DirectionPathOverlay(gp2, gp2));

      myMapView.getController().animateTo(startGP);
      myMapView.setBuiltInZoomControls(true);
      myMapView.displayZoomControls(true);

     }

     @Override
     protected boolean isRouteDisplayed() {
      // TODO Auto-generated method stub
      return false;
     }

Layout

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello" />

   <com.google.android.maps.MapView
           android:id="@+id/mapview"
             android:layout_width="fill_parent"
             android:layout_height="fill_parent"
             android:apiKey="034BXAeVNYe1Ob063cZUpablCB_0y7xjEGD3RhQ"
             />

Logcat 详细信息

08-10 09:03:20.216: W/dalvikvm(305): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
08-10 09:03:20.246: E/AndroidRuntime(305): FATAL EXCEPTION: main
08-10 09:03:20.246: E/AndroidRuntime(305): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.hands/com.hands.DrawlineActivity}: java.lang.NullPointerException
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread.access$2300(ActivityThread.java:125)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.os.Handler.dispatchMessage(Handler.java:99)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.os.Looper.loop(Looper.java:123)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread.main(ActivityThread.java:4627)
08-10 09:03:20.246: E/AndroidRuntime(305):       at java.lang.reflect.Method.invokeNative(Native Method)
08-10 09:03:20.246: E/AndroidRuntime(305):       at java.lang.reflect.Method.invoke(Method.java:521)
08-10 09:03:20.246: E/AndroidRuntime(305):       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-10 09:03:20.246: E/AndroidRuntime(305):       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-10 09:03:20.246: E/AndroidRuntime(305):       at dalvik.system.NativeStart.main(Native Method)
08-10 09:03:20.246: E/AndroidRuntime(305): Caused by: java.lang.NullPointerException
08-10 09:03:20.246: E/AndroidRuntime(305):       at com.hands.DrawlineActivity.getDirectionData(DrawlineActivity.java:111)
08-10 09:03:20.246: E/AndroidRuntime(305):       at com.hands.DrawlineActivity.onCreate(DrawlineActivity.java:44)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-10 09:03:20.246: E/AndroidRuntime(305):       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
08-10 09:03:20.246: E/AndroidRuntime(305):       ... 11 more

更新了 getDirection 方法代码

包com.hands；

导入 java.net.HttpURLConnection; 导入java.net.URL；

导入 javax.xml.parsers.DocumentBuilder; 导入 javax.xml.parsers.DocumentBuilderFactory;

导入 org.w3c.dom.Document； 导入 org.w3c.dom.Node; 导入 org.w3c.dom.NodeList;

导入 android.os.Bundle； 导入 android.util.Log；

导入 com.google.android.maps.GeoPoint; 导入 com.google.android.maps.MapActivity; 导入 com.google.android.maps.MapController; 导入 com.google.android.maps.MapView;

公共类 DrawlineActivity 扩展 MapActivity { 地图视图 myMapView = null; MapController myMC = null; GeoPoint geoPoint = null; @覆盖 公共无效onCreate（捆绑保存实例状态）{ super.onCreate(savedInstanceState);

  setContentView(R.layout.main);
  myMapView = (MapView) findViewById(R.id.mapview);

  geoPoint = null;
  myMapView.setSatellite(false);
  double fromLat = 12.303534;
  double fromLong = 76.64611;
  double toLat = 12.9715987;
  double toLong = 77.5945627;

  String sourceLat = Double.toString(fromLat);
  String sourceLong = Double.toString(fromLong);
  String destinationLat = Double.toString(toLat);
  String destinationLong = Double.toString(toLong);

  String pairs[] = getDirectionData(sourceLat,sourceLong, destinationLat, destinationLong );
  String[] lngLat = pairs[0].split(",");

  // STARTING POINT
  GeoPoint startGP = new GeoPoint((int) (Double.parseDouble(lngLat[1]) * 1E6), (int) (Double.parseDouble(lngLat[0]) * 1E6));

  myMC = myMapView.getController();
  geoPoint = startGP;
  myMC.setCenter(geoPoint);
  myMC.setZoom(10);
  myMapView.getOverlays().add(new DirectionPathOverlay(startGP, startGP));

  // NAVIGATE THE PATH

  GeoPoint gp1;
  GeoPoint gp2 = startGP;

  for (int i = 1; i < pairs.length; i++) {
   lngLat = pairs[i].split(",");
   gp1 = gp2;
   // watch out! For GeoPoint, first:latitude, second:longitude

   gp2 = new GeoPoint((int) (Double.parseDouble(lngLat[1]) * 1E6),(int) (Double.parseDouble(lngLat[0]) * 1E6));
   myMapView.getOverlays().add(new DirectionPathOverlay(gp1, gp2));
   Log.d("xxx", "pair:" + pairs[i]);
  }

  // END POINT
  myMapView.getOverlays().add(new DirectionPathOverlay(gp2, gp2));

  myMapView.getController().animateTo(startGP);
  myMapView.setBuiltInZoomControls(true);
  myMapView.displayZoomControls(true);

 }

 @Override
 protected boolean isRouteDisplayed() {
  // TODO Auto-generated method stub
  return false;
 }

 private String[] getDirectionData(String sourceLat, String sourceLong, String destinationLat, String destinationLong) {


  String urlString = "http://maps.google.com/maps?f=d&hl=en&" +"saddr="+sourceLat+","+sourceLong+"&daddr="+destinationLat+","+destinationLong + "&ie=UTF8&0&om=0&output=kml";
  Log.d("URL", urlString);
  Document doc = null;
  HttpURLConnection urlConnection = null;
  URL url = null;
  String pathConent = "";

  try {

   url = new URL(urlString.toString());
   urlConnection = (HttpURLConnection) url.openConnection();
   urlConnection.setRequestMethod("GET");
   urlConnection.setDoOutput(true);
   urlConnection.setDoInput(true);
   urlConnection.connect();
   DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
   DocumentBuilder db = dbf.newDocumentBuilder();
   doc = db.parse(urlConnection.getInputStream());

  } catch (Exception e) {
  }

  NodeList nl = doc.getElementsByTagName("LineString");
  for (int s = 0; s < nl.getLength(); s++) {
   Node rootNode = nl.item(s);
   NodeList configItems = rootNode.getChildNodes();
   for (int x = 0; x < configItems.getLength(); x++) {
    Node lineStringNode = configItems.item(x);
    NodeList path = lineStringNode.getChildNodes();
    pathConent = path.item(0).getNodeValue();
   }
  }
  String[] tempContent = pathConent.split(" ");
  return tempContent;
 }

}

正如 logcat 所解释的，当您调用 getDirectionData() 方法时，您将收到 NullPointerException。上面的代码中没有显示这个方法。您可以添加这个方法以便我们看看问题出在哪里吗？

Edit:感谢您添加 getDirectionData() 方法。目前尚不清楚问题出在哪里，但一个问题是您有一个空的 catch 块 - 这将吞掉异常，然后您继续处理代码。例如，如果该行

doc = db.parse(urlConnection.getInputStream());

抛出异常或返回 null，然后您尝试从 null 对象获取 NodeList - 这会给您带来空指针异常。我建议在此方法的开头放置一个断点并逐步执行它，同时检查变量。这将确定问题的根源。