無法啓動網絡地圖活動（NullPointerException）

Question

我發現this project的知名度爲commonsware。我試圖啓動它，但我有一個空指針異常： 以下是代碼：

public class WebMapActivity extends Activity { 
     private static String PROVIDER="gps"; 
     private WebView browser; 
     private LocationManager myLocationManager=null; 

     @Override 
     public void onCreate(Bundle icicle) { 
     super.onCreate(icicle); 
     setContentView(R.layout.main); 
     browser=(WebView)findViewById(R.id.webview); 

     myLocationManager=(LocationManager)getSystemService(Context.LOCATION_SERVICE); 

     browser.getSettings().setJavaScriptEnabled(true); 
     browser.addJavascriptInterface(new Locater(), "locater"); 
     browser.loadUrl("http://gmaps-samples.googlecode.com/svn/trunk/articles-android-webmap/simple-android-map.html"); 
     } 

     @Override 
     public void onResume() { 
     super.onResume(); 
     myLocationManager.requestLocationUpdates(PROVIDER, 0, 
                0, 
                onLocation); 
     } 

     @Override 
     public void onPause() { 
     super.onPause(); 
     myLocationManager.removeUpdates(onLocation); 
     } 

     LocationListener onLocation=new LocationListener() { 
     public void onLocationChanged(Location location) { 
      StringBuilder buf=new StringBuilder("javascript:whereami("); 

      buf.append(String.valueOf(location.getLatitude())); 
      buf.append(","); 
      buf.append(String.valueOf(location.getLongitude())); 
      buf.append(")"); 

      browser.loadUrl(buf.toString()); 
     } 

     public void onProviderDisabled(String provider) { 
      // required for interface, not used 
     } 

     public void onProviderEnabled(String provider) { 
      // required for interface, not used 
     } 

     public void onStatusChanged(String provider, int status, 
             Bundle extras) { 
      // required for interface, not used 
     } 
     }; 

     public class Locater { 
     public String getLocation() throws JSONException { 
      Location loc=myLocationManager.getLastKnownLocation(PROVIDER); 

      if (loc==null) { 
      return(null); 
      } 

      JSONObject json=new JSONObject(); 

      json.put("lat", loc.getLatitude()); 
      json.put("lon", loc.getLongitude()); 

      return(json.toString()); 
     } 
     } 
    } 

的logcat：

02-29 22:10:35.096: E/AndroidRuntime(885): FATAL EXCEPTION: main 
02-29 22:10:35.096: E/AndroidRuntime(885): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gatec.tunisiana/com.android.airplane.WebMapActivity}: java.lang.NullPointerException 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.os.Looper.loop(Looper.java:130) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread.main(ActivityThread.java:3683) 
02-29 22:10:35.096: E/AndroidRuntime(885): at java.lang.reflect.Method.invokeNative(Native Method) 
02-29 22:10:35.096: E/AndroidRuntime(885): at java.lang.reflect.Method.invoke(Method.java:507) 
02-29 22:10:35.096: E/AndroidRuntime(885): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
02-29 22:10:35.096: E/AndroidRuntime(885): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
02-29 22:10:35.096: E/AndroidRuntime(885): at dalvik.system.NativeStart.main(Native Method) 
02-29 22:10:35.096: E/AndroidRuntime(885): Caused by: java.lang.NullPointerException 
02-29 22:10:35.096: E/AndroidRuntime(885): at com.android.airplane.WebMapActivity.onCreate(WebMapActivity.java:26) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
02-29 22:10:35.096: E/AndroidRuntime(885): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
02-29 22:10:35.096: E/AndroidRuntime(885): ... 11 more 

我不知道爲什麼它不能launchs活動。非常感謝您的幫助。

Answer 1

很高興你的答案。爲了將來的參考，看看你的日誌。我知道你張貼了他們，但真正的答案就像中途。

02-29 22:10:35.096: E/AndroidRuntime(885): Caused by: java.lang.NullPointerException 
02-29 22:10:35.096: E/AndroidRuntime(885): at com.android.airplane.WebMapActivity.onCreate(WebMapActivity.java:26) 

在第二行，它說.WebMapActivity.onCreate(WebMapActivity.java:26)所以你知道它在26行的GO在在OnCreate（）的WebMapActivity到該行並找出哪些是null值，該行的關鍵。

像ByteMe說......在該行

browser=(WebView)findViewById(R.id.webview); 

Nothing可能引起一個NullPointerException，除非沒有被發現的WebView。