致命錯誤，當我嘗試啓動我的自定義MapActivity

Question

這在一個有點複雜的問題，所以仔細閱讀。

我試圖實現一個地圖，

- 顯示我的當前位置，

- 當我點擊在地圖上的一個點，應用程序應該把自定義的GeoPoint獲取經緯度傳遞這些以活動來創建一個新的酒吧對象

-the地圖上開始必須出示酒館的位置

之前保存繼this tutorial我創建了這些類

類MyMap中：

public class MyMap extends MapActivity implements LocationListener { 
    private MapView mapView; 
    private LocationManager locManager; 
    private MapLocationOverlay itemizedOverlay; 
    GeoPoint point ; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     // Inflate our UI from its XML layout description. 
     setContentView(R.layout.mymap); 

     mapView = (MapView) findViewById(R.id.mapView); 

     // invalidate the map in order to show changes 
     mapView.invalidate(); 

     MapController controller = mapView.getController(); 


     // Use the location manager through GPS 
     locManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
     locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 
       0, this); 

     //get the current location (last known location) from the location manager 
     Location location = locManager 
       .getLastKnownLocation(LocationManager.GPS_PROVIDER); 



      //if location found display as a toast the current latitude and longitude 
     if (location != null) { 
      point = new GeoPoint((int)(location.getLatitude()*1E6),(int)(location.getLongitude() *1E6)); 
      Toast.makeText(
        this, 
        "Current location:\nLatitude: " + location.getLatitude() 
          + "\n" + "Longitude: " + location.getLongitude(), 
        Toast.LENGTH_LONG).show(); 


      controller.animateTo(point); 
      controller.setZoom(13); 

     } else { 

      Toast.makeText(this, "Cannot fetch current location!", 
        Toast.LENGTH_LONG).show(); 
     } 


     // fetch the drawable - the pin that will be displayed on the map 
     Drawable drawable = this.getResources().getDrawable(R.drawable.pin_custom); 

     // create and add an OverlayItem to the MyItemizedOverlay list 
     OverlayItem overlayItem = new OverlayItem(point, "", ""); 
     itemizedOverlay = new MapLocationOverlay(drawable,this); 
     itemizedOverlay.addOverlay(overlayItem); 

     // add the overlays to the map 
     mapView.getOverlays().add(itemizedOverlay); 
     mapView.invalidate(); 

     GestureDetector gd=new GestureDetector(this, new MyGestureDetector()); 
     itemizedOverlay.setGestureDetector(gd); 

     //when the current location is found – stop listening for updates (preserves battery) 
     locManager.removeUpdates(this); 
    } 





    protected boolean isRouteDisplayed() { 
     return false; 

    } 

    /* When the activity starts up, request updates */ 

    protected void onResume() { 
     super.onResume(); 
     locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 
       0, this); 
    } 


    protected void onPause() { 
     super.onPause(); 
     locManager.removeUpdates(this); //activity pauses => stop listening for updates 
    } 

    public void onLocationChanged(Location location) { 

    } 



    public void onProviderDisabled(String provider) { 

    } 


    public void onProviderEnabled(String provider) { 

    } 


    public void onStatusChanged(String provider, int status, Bundle extras) { 

    } 

    public class MyGestureDetector extends SimpleOnGestureListener { 


     public boolean onSingleTapConfirmed(MotionEvent event) { 

      // fetch the correspondent point from the map 
      GeoPoint p = mapView.getProjection().fromPixels((int) event.getX(),(int) event.getY()); 

      // create an overlay item and clear all others 
      OverlayItem o = new OverlayItem(p, null, null); 
      itemizedOverlay.clear(); 
      itemizedOverlay.addOverlay(o); 

      // add the overlay item 
      mapView.getOverlays().clear(); 
      mapView.getOverlays().add(itemizedOverlay); 
      mapView.invalidate(); 

      Geocoder geoCoder = new Geocoder(getBaseContext(), 
        Locale.getDefault()); 

      // get the address based on the coordinates 
      try { 
       List<Address> addresses = geoCoder.getFromLocation(p.getLatitudeE6()/1E6, p.getLongitudeE6()/1E6, 1); 

       String addressString = ""; 
       if (addresses.size() > 0) { 
        for (int i = 0; i < addresses.get(0) 
          .getMaxAddressLineIndex(); i++) 
         addressString += addresses.get(0).getAddressLine(i) 
           + " - "; 
       } 

       Toast.makeText(getBaseContext(), addressString, 
         Toast.LENGTH_SHORT).show(); 

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

      return true; 
     } 

     public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, 
       float velocityY) { 
      return super.onFling(e1, e2, velocityX, velocityY); 
     } 

     public boolean onDown(MotionEvent e) { 
      return false; 
     } 
    } 


} 

和類MapLocationOverlay：

public class MapLocationOverlay extends ItemizedOverlay<OverlayItem> { 

     private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>(); 
     private GestureDetector gestureDetector; 

     private List<Pub> pubList; 
     private Context context; 



     public MapLocationOverlay(Context context, List<Pub> pubList, Drawable marker) { 
      super(boundCenterBottom(marker)); 
      try{ 
       this.context = context; 
       this.pubList = pubList; 
       if (pubList == null) { 
        pubList = new ArrayList<Pub>(); 
       } 
       populate(); 
      } 
      catch(RuntimeException e){ 

      } 

     } 

     public MapLocationOverlay(Drawable defaultMarker, Context ctx) { 
      super(boundCenterBottom(defaultMarker)); 

     } 

     @Override 
     protected OverlayItem createItem(int i) { 
      try{ 
      Pub c=pubList.get(i); 
       GeoPoint point = 
         new GeoPoint((int) (c.getLatitude() * 1e6), (int) (c.getLongitude() * 1e6)); 
       return new OverlayItem(point, c.getName(), null); 
      } 
      catch(RuntimeException e){ 

      } 
      return mOverlays.get(i); 
     } 

     public void addOverlay(OverlayItem overlay) { 
      mOverlays.add(overlay); 
      populate(); 
     } 

     public void clear() { 

      mOverlays.clear(); 
      populate(); 
     } 

     @Override 
     public boolean onTap(final int index) { 
      Pub c=pubList.get(index); 
      final String name=c.getName(); 
      final String description=c.getDescription(); 
      final String street=c.getStreet(); 
     // BrewLocation brewLocation = brewLocations.get(index); 
      AlertDialog.Builder builder = new AlertDialog.Builder(context); 
      builder.setTitle("Visualizzare la nota "+name+"?") 
        .setPositiveButton("Si", new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
         Intent pubDetails = new Intent(context, InfoPub.class); 
         pubDetails.putExtra("name", name); 
         pubDetails.putExtra("description", description); 
         pubDetails.putExtra("street", street); 
         context.startActivity(pubDetails); 
         } 
        }).setNegativeButton("No", new DialogInterface.OnClickListener() { 
         public void onClick(DialogInterface dialog, int id) { 
         dialog.cancel(); 
         } 
        }); 
      AlertDialog alert = builder.create(); 
      alert.show(); 

      return true; // we'll handle the event here (true) not pass to another overlay (false) 
     } 


     /** 
     * Override this method to handle a "tap" on a balloon. By default, does nothing 
     * and returns false. 
     * 
     * @param index - The index of the item whose balloon is tapped. 
     * @return true if you handled the tap, otherwise false. 
     */ 
     protected boolean onBalloonTap(int index) { 
      return false; 
     } 

      @Override 
      public boolean onTouchEvent(MotionEvent event, MapView mapView) { 

       // when the user lifts its finger 
       if (gestureDetector.onTouchEvent(event)) { 
        return true; 
       } 

       return false; 
       } 

      public GestureDetector getGestureDetector() { 
        return gestureDetector; 
       } 

      public void setGestureDetector(GestureDetector gestureDetector) { 
       this.gestureDetector = gestureDetector; 
      } 

     @Override 
     public int size() { 
      //return pubList.size(); 
      return mOverlays.size(); 
     } 



    } 

不是完全完成，但應該運行，根據教程其次，不幸的是，當我嘗試啓動活動應用程序崩潰與致命錯誤。

這是錯誤堆棧：

10-13 17:25:56.109: E/AndroidRuntime(28215): FATAL EXCEPTION: main 
10-13 17:25:56.109: E/AndroidRuntime(28215): java.lang.RuntimeException: Unable to start activity ComponentInfo{it.myapp.mymapapp/it.myapp.mymapapp.MyMap}: java.lang.NullPointerException 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.os.Looper.loop(Looper.java:130) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread.main(ActivityThread.java:3687) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at java.lang.reflect.Method.invokeNative(Native Method) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at java.lang.reflect.Method.invoke(Method.java:507) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at dalvik.system.NativeStart.main(Native Method) 
10-13 17:25:56.109: E/AndroidRuntime(28215): Caused by: java.lang.NullPointerException 
10-13 17:25:56.109: E/AndroidRuntime(28215): at com.google.android.maps.ItemizedOverlay.populate(ItemizedOverlay.java:312) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at it.myapp.mymapapp.utility.MapLocationOverlay.addOverlay(MapLocationOverlay.java:72) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at it.myapp.mymapapp.MyMap.onCreate(MyMap.java:89) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
10-13 17:25:56.109: E/AndroidRuntime(28215): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
10-13 17:25:56.109: E/AndroidRuntime(28215): ... 11 more 

我怎麼能解決這個問題？ 缺少什麼？

Answer 1

您並未初始化point的onCreate()，除非您獲得有效的lastKnownLocation()。

這個未初始化的point被添加到OverlayItem，它被添加到ItemizedOverlay。

當Mapview試圖讓Geopoint繪製標記時，它會得到一個null和bummmm！

只需更換：

由：

GeoPoint point = new Geopoint(0,0); 

，它不會再崩潰。

Answer 2

你createItem()實現相當奇怪：

1. 你抓RuntimeException，什麼也不做它。如果沒有別的，你應該記錄異常，特別是只要你的代碼有問題。

2. 你size()方法是基於關閉的mOverlays，但你不使用createItem()mOverlays（除非發生不當RuntimeException）。請始終使用mOverlays或完全清除它。

除此之外，一些ItemizedOverlay預計不會null確實null。一種可能性是「片段」（第OverlayItem構造函數的第三個參數），您將其設置爲null。另一種可能性是c.getName()正在返回null，或許ItemizedOverlay需要名稱爲非null。

如果沒有別的，回到原來的代碼從那個博客文章，得到那個工作，然後緩慢修改它有你想要的功能，隨時測試。