doInBackground上的AsyncTask错误

Question

有人可以帮我找出为什么AsyncTask偶尔会崩溃？

赫雷什我的代码：

public class statuspage extends MapActivity { 

LocationManager locationManager; 
MapView mapView; 
Criteria criteria; 
Location location; 
Geocoder gc; 
Address address; 

String bestProvider; 
String LOCATION_SERVICE = "location"; 
String addressString = "No address found"; 
StringBuilder sb; 

private MapController mapController; 
private MyLocationOverlay myLocation; 

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.statuspage); 

    // Get Mapping Controllers etc // 
    mapView = (MapView) findViewById(R.id.mapView); 
    mapController = mapView.getController(); 
    mapController.setZoom(17); 
    mapView.setBuiltInZoomControls(true); 

    // Add the MyLocationOverlay // 
    myLocation = new MyLocationOverlay(this, mapView); 
    mapView.getOverlays().add(myLocation); 
    myLocation.enableMyLocation(); 

    // Animates the map to GPS Position // 
    myLocation.runOnFirstFix(new Runnable() { 
     public void run() { 
      mapController.animateTo(myLocation.getMyLocation()); 
     } 
    }); 
} 

@Override 
protected boolean isRouteDisplayed() { 

    // Executes GeoCoding AsyncTask // 
    new GeoCoder().execute(); 

    // Location Manager Intiation 
    locationManager = (LocationManager) statuspage.this 
      .getSystemService(LOCATION_SERVICE); 
    criteria = new Criteria(); 

    // More accurate, GPS fix. 
    criteria.setAccuracy(Criteria.ACCURACY_FINE); // More accurate, GPS fix. 
    bestProvider = locationManager.getBestProvider(criteria, true); 
    location = locationManager.getLastKnownLocation(bestProvider); 
    if (location != null) { 

     // Latitude and Longitude TextView 
     TextView etlongitude = (TextView) findViewById(R.id.etlongitude); 
     TextView etlatitude = (TextView) findViewById(R.id.etlatitude); 

     double latitude = location.getLatitude(); 
     double longitude = location.getLongitude(); 

     // Latitude and Longitude TextView Display Coordinates // 
     etlongitude.setText((longitude) + ""); 
     etlatitude.setText((latitude) + ""); 

     // locationManager.removeUpdates((LocationListener) location); 
     locationManager = null; 

    } 

    return false; 
} 

class GeoCoder extends AsyncTask<Void, Void, Void> { 

    @Override 
    protected Void doInBackground(Void... params) { 
     Log.d("Class == GeoCoder", "AsyncTask == doInBackGround"); 

     double latitude = location.getLatitude(); 
     double longitude = location.getLongitude(); 

     gc = new Geocoder(statuspage.this, Locale.getDefault()); 
     try { 

      List<Address> addresses = gc.getFromLocation(latitude, 
        longitude, 1); 

      sb = new StringBuilder(); 
      if (addresses != null && addresses.size() > 0) { 
       address = addresses.get(0); 

       int noOfMaxAddressLine = address.getMaxAddressLineIndex(); 
       if (noOfMaxAddressLine > 0) { 
        for (int i = 0; i < address.getMaxAddressLineIndex(); i++) { 
         sb.append(address.getAddressLine(i)).append("\n"); 
        } 
        addressString = sb.toString(); 
       } 
      } 
     } catch (Exception e) { 

      addressString = e.toString(); 
     } 
     return null; 

    } 


    @Override 
    protected void onPostExecute(Void result) { 

     TextView scrollview = (TextView) findViewById(R.id.scrollview); 
     scrollview.setText("Your location:" + "\n" 
       + "(Accurate to 500 meters)" + "\n" + (addressString)); 

     Log.d("Class == GeoCoder", "AsyncTask == onPostExecute"); 
     return; 
    } 

} 

@Override 
protected void onResume() { 
    super.onResume(); 
    myLocation.enableMyLocation(); 
} 

@Override 
protected void onDestroy() { 
    super.onDestroy(); 
    new GeoCoder(); 

} 

@Override 
protected void onPause() { 
    super.onPause(); 
    new GeoCoder().cancel(true); 
    myLocation.disableMyLocation(); 
} 

@Override 
public void onStop() { 
    super.onStop(); 
    new GeoCoder().cancel(true); 

} 

@Override 
public void onBackPressed() { 
    new GeoCoder().cancel(true); 

    // Button OnClick Vibrating Service 
    Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE); 

    // Vibrate Service 
    vib.vibrate(50); 

    startActivity(new Intent(statuspage.this, AgentPortalActivity.class)); 
    statuspage.this.finish(); 

    /** Fading Transition Effect */ 
    overridePendingTransition(R.anim.fadein, R.anim.fadeout); 

    return; 

} 
} 

赫雷什我的日志：

04-20 09:23:15.449: D/Class == GeoCoder(22493): AsyncTask == onPostExecute 
04-20 09:23:16.082: D/Dialog(22493): dialog button was clicked 
04-20 09:23:16.136: W/MapActivity(22493): Recycling dispatcher android_maps_conflict_avoidance.com.google.googlenav.datarequest.DataRequestDispatcher@40685938 
04-20 09:23:16.140: V/MapActivity(22493): Recycling map object. 
04-20 09:23:16.167: I/Maps.MyLocationOverlay(22493): Request updates from gps 
04-20 09:23:16.167: I/Maps.MyLocationOverlay(22493): Request updates from network 
04-20 09:23:16.179: I/Maps.MyLocationOverlay(22493): Request updates from gps 
04-20 09:23:16.183: I/Maps.MyLocationOverlay(22493): Request updates from network 
04-20 09:23:16.238: I/MapActivity(22493): Handling network change notification:CONNECTED 
04-20 09:23:16.238: E/MapActivity(22493): Couldn't get connection factory client 
04-20 09:23:16.281: D/Class == GeoCoder(22493): AsyncTask == doInBackGround 
04-20 09:23:16.300: W/dalvikvm(22493): threadid=28: thread exiting with uncaught exception (group=0x40015578) 
04-20 09:23:16.390: E/AndroidRuntime(22493): FATAL EXCEPTION: AsyncTask #16 
04-20 09:23:16.390: E/AndroidRuntime(22493): java.lang.RuntimeException: An error occured while executing doInBackground() 
04-20 09:23:16.390: E/AndroidRuntime(22493): at android.os.AsyncTask$3.done(AsyncTask.java:200) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.FutureTask.setException(FutureTask.java:125) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.FutureTask.run(FutureTask.java:138) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.lang.Thread.run(Thread.java:1019) 
04-20 09:23:16.390: E/AndroidRuntime(22493): Caused by: java.lang.NullPointerException 
04-20 09:23:16.390: E/AndroidRuntime(22493): at com.jetdelivery.mobile.statuspage$GeoCoder.doInBackground(statuspage.java:111) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at com.jetdelivery.mobile.statuspage$GeoCoder.doInBackground(statuspage.java:1) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at android.os.AsyncTask$2.call(AsyncTask.java:185) 
04-20 09:23:16.390: E/AndroidRuntime(22493): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306) 
04-20 09:23:16.390: E/AndroidRuntime(22493): ... 4 more 

下面有行111： 双纬度= location.getLatitude（）;

我一直在试图找出几天，试图在这里搜索，在谷歌上，跟着一些例子，没有运气。

谢谢你们！

Answer 1

您在初始化isRouteDisplayed（）中的位置对象之前启动GeoCoder任务。你应该得到的位置和测试空后启动它，该行后表示：

if (location != null) { 

你也可以测试它在doInBackground空指针，但没有它整个方法看起来毫无用处。

有时会发生崩溃，因为您不知道任务何时开始。这意味着有时创建GeoCoder任务的线程将继续运行，初始化位置对象而不是任务需要控制。然而，这只是有时候发生。在其他情况下，任务在第一个线程到达用于定位和崩溃的初始化代码之前开始。