無法運行後臺服務

Question

我想在後臺服務中使用LocationListener類來每次接收用戶的當前位置，然後將它與存儲在我的數據庫中的一些數據進行比較。但我剛開的錯誤，當我嘗試這樣做，

package com.example.alert; 

    import android.app.Service; 
    import android.content.Context; 
    import android.content.Intent; 
    import android.location.Location; 
    import android.location.LocationListener; 
    import android.location.LocationManager; 
    import android.media.MediaPlayer; 
    import android.os.Bundle; 
import android.os.IBinder; 
import android.widget.Toast; 

public class service extends Service{ 
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 

@Override 
public IBinder onBind(Intent arg0) { 
    // TODO Auto-generated method stub 
    return null; 
} 

public void onCreate() { 
    Toast.makeText(this, "Background Service Created", Toast.LENGTH_LONG).show(); 



} 

public void onDestroy() { 
    Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show(); 


} 

public void onStart(Intent intent, int startid) { 

    Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show(); 
    Intent myIntent=new Intent(service.this,CurrentLocation.class); 
    startActivity(myIntent); 
    } 
} 

，這裏是我的logcat

11-10 04:54:54.819: E/AndroidRuntime(768): FATAL EXCEPTION: main 
11-10 04:54:54.819: E/AndroidRuntime(768): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.alert/com.example.alert.service}: java.lang.NullPointerException 
    11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983) 
    11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.os.Looper.loop(Looper.java:137) 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.app.ActivityThread.main(ActivityThread.java:4745) 
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.reflect.Method.invokeNative(Native Method) 
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.reflect.Method.invoke(Method.java:511) 
11-10 04:54:54.819: E/AndroidRuntime(768): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
11-10 04:54:54.819: E/AndroidRuntime(768): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
11-10 04:54:54.819: E/AndroidRuntime(768): at dalvik.system.NativeStart.main(Native Method) 
11-10 04:54:54.819: E/AndroidRuntime(768): Caused by: java.lang.NullPointerException 
11-10 04:54:54.819: E/AndroidRuntime(768): at android.content.ContextWrapper.getSystemService(ContextWrapper.java:416) 
11-10 04:54:54.819: E/AndroidRuntime(768): at com.example.alert.service.<init>(service.java:15) 
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.Class.newInstanceImpl(Native Method) 
11-10 04:54:54.819: E/AndroidRuntime(768): at java.lang.Class.newInstance(Class.java:1319) 

這裏的位置監聽器的代碼

package com.example.alert; 

    import android.app.Activity; 
    import android.content.Context; 
    import android.location.Location; 
    import android.location.LocationListener; 
    import android.location.LocationManager; 
    import android.os.Bundle; 
import android.widget.Toast; 

public class CurrentLocation extends Activity { 
LocationManager lm ; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    /* Use the LocationManager class to obtain GPS locations */ 
    LocationListener ll = new MyLocationListener(); 
    //lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 5*60*10000, 0, ll); 
    lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, ll); 

} 



/* Class My Location Listener */ 
public class MyLocationListener implements LocationListener 
{ 

    public void onLocationChanged(Location loc) 
    { 
     if(loc!=null) 
     { 
      double x; 
      String Text = "My current location is: " +"Latitud = " + loc.getLatitude() +"Longitud = " + loc.getLongitude(); 
      Toast.makeText(getApplicationContext(),Text,Toast.LENGTH_SHORT).show();  
      //for loop, alerters retrieving one by one 
      //x= calcDistance(loc.getLatitude(),loc.getLongitude(),,); 
      //if(x<1) 
      // distance < 1, retrieve data from DB and trigger 
     } 
    } 


    public void onProviderDisabled(String provider) 
    { 
     Toast.makeText(getApplicationContext(),"Gps Disabled - @From :Alert Me",Toast.LENGTH_SHORT).show(); 
    } 


    public void onProviderEnabled(String provider) 
    { 
     Toast.makeText(getApplicationContext(),"Gps Enabled - @From :Alert Me",Toast.LENGTH_SHORT).show(); 
    } 


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

    } 

}/* End of Class MyLocationListener */ 

public double calcDistance(double latA, double longA, double latB, double longB) { 

    double theDistance = (Math.sin(Math.toRadians(latA)) * Math.sin(Math.toRadians(latB)) + Math.cos(Math.toRadians(latA)) * Math.cos(Math.toRadians(latB)) * Math.cos(Math.toRadians(longA - longB))); 
    return new Double((Math.toDegrees(Math.acos(theDistance))) * 69.09*1.6093); 
} 


} 

清單文件

其餘

<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.example.alert" 
android:versionCode="1" 
android:versionName="1.0" > 

<uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="15" /> 

<application 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name=".MainActivity" 
     android:label="@string/title_activity_main" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

    <activity android:name=".Instructions" android:label="Instructions"></activity> 
    <activity android:name=".AboutApp" android:label="About ALERT ME!"></activity> 

    <activity android:name=".ViewAlerters" android:label="Alerters Active"></activity> 
    <activity android:name=".AddAlerter" android:label="Add an Alerter"></activity> 
    <activity android:name=".EditAlerter" android:label="Edit an alerter"></activity> 
    <activity android:name=".AddLocation" android:label="Add Location to Alerter"></activity> 
    <activity android:name=".AddTrigger" android:label="Add trigger to Alerter"></activity> 


    <activity android:name=".SilVib" android:label="Silent/Vibrate Trigger"></activity> 
    <activity android:name=".CallMode" android:label="Call Mode Trigger"></activity> 
    <activity android:name=".service"></activity> 
    <activity android:name=".Status_Notify"></activity> 
    <activity android:name=".Notifier"></activity>  
    <activity android:name=".Message"></activity> 
    <activity android:name=".Message_sent"></activity> 
    <activity android:name=".StoringEntire"></activity> 
    <activity android:name=".CurrentLocation"></activity> 


    <uses-library android:name="com.google.android.maps"/> 
<service 
    android:enabled="true" 
android:name=".service"/> 
     </application> 
<uses-permission android:name="android.permission.INTERNET"/> 
<uses-permission android:name="android.permission.SEND_SMS"/> 
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/> 
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/> 
<uses-permission android:name="android.permission.ACCESS_BACKGROUND_SERVICE"/> 


</manifest> 

Answer 1

LogC在狀態：

Caused by: java.lang.NullPointerException 
    at android.content.ContextWrapper.getSystemService(ContextWrapper.java:416) 
    at com.example.alert.service.<init>(service.java:15) 

只需等待上下文通過移動這個代碼初始化爲onCreate()：

public class service extends Service { 
    LocationManager lm; 

    @Override 
    public void onCreate() { 
     // This line needs an existing context 
     lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
     Toast.makeText(this, "Background Service Created", Toast.LENGTH_LONG).show(); 
    } 

    // etc 

Answer 2

確保您已經增值服務給AndroidManifest文件

一Service是一個應用程序組件，它表示應用程序希望在不與用戶交互的情況下執行長時間運行的操作，或者提供其他應用程序使用的功能。每個服務類必須在其包的AndroidManifest.xml中有相應的聲明。服務可以使用Context.startService（）和Context.bindService（）來啓動。

Answer 3

使用此代碼，我的朋友，並根據您的需要

public class MainActivity extends Activity { 
    Button btnStart, btnStop; 
    public static Context mContext; 
    Intent it; 
    public LocationManager manager; 
    public boolean isGPSEnabled = false; 
    boolean isNetworkEnabled = false; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     mContext = this; 
     manager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
     isGPSEnabled = manager.isProviderEnabled(LocationManager.GPS_PROVIDER); 
     // getting network status 
     isNetworkEnabled = manager 
       .isProviderEnabled(LocationManager.NETWORK_PROVIDER); 
     btnStart = (Button) findViewById(R.id.btnStart); 
     btnStop = (Button) findViewById(R.id.btnStop); 
     btnStart.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       /*if (isGPSEnabled) { 
        startService(getIntent()); 
       } 
       else 
       { 
        Toast.makeText(MainActivity.this, "Please oN Gps ", 
          Toast.LENGTH_LONG).show(); 
       }*/ 
       startService(getIntent()); 
      } 
     }); 
     btnStop.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 

       stopService(getIntent()); 
      } 
     }); 
    } // on create ends 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    public Intent getIntent() { 
     it = new Intent(mContext, MyService.class); 
     return it; 
    } // method ends 

    public static Context getContextForService() { 
     return mContext; 
    } // methods ends 
} // final class ends 

更改這裏是你的位置服務

public class MyService extends Service { 
    // flag for GPS status 
    public static LocationManager manager; 
    public static boolean isGPSEnabled = false; 
    public static double lattitude = 0; 
    public static double longitude = 0; 
    int count = 0; 
    // flag for network status 
    boolean isNetworkEnabled = false; 

    // flag for GPS status 
    boolean canGetLocation = false; 
    MyFile myFile; 

    @Override 
    public IBinder onBind(Intent intent) { 
     // TODO Auto-generated method stub 
     return null; 
    } // method ends 

    @Override 
    public int onStartCommand(Intent intent, int flags, int startId) { 

     super.onStartCommand(intent, flags, startId); 
     System.out.println("On Start Command is called "); 
     return START_STICKY; 
    } // method ends 

    @Override 
    public void onCreate() { 
     // TODO Auto-generated method stub 
     super.onCreate(); 
     System.out.println("Service is created//////////// "); 
     // start asyntask to get locations 

     new GetLocations().execute(); 
    }// on create ends 

    @Override 
    public void onDestroy() { 
     // TODO Auto-generated method stub 
     super.onDestroy(); 
     System.out.println("Service is Destroyed //////////// "); 
     if (manager != null && isGPSEnabled == true) { 
      manager.removeUpdates(mylistener); 
      System.out.println("Service is Destroyed under if //////////// "); 
     } 

    } // method ends 

    public class GetLocations extends AsyncTask<Void, Void, Void> { 

     @Override 
     protected void onPreExecute() { 
      // TODO Auto-generated method stub 
      super.onPreExecute(); 
      manager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
      // getting GPS status 
      isGPSEnabled = manager 
        .isProviderEnabled(LocationManager.GPS_PROVIDER); 
      // getting network status 
      isNetworkEnabled = manager 
        .isProviderEnabled(LocationManager.NETWORK_PROVIDER); 
      if (isGPSEnabled) { 
       /* 
       * Criteria criteria = new Criteria(); String bestProvider = 
       * manager.getBestProvider(criteria, false); Location location = 
       * manager.getLastKnownLocation(bestProvider); double lat 
       * =location.getLatitude(); double longi 
       * =location.getLongitude(); 
       * System.out.println("getting location continous ////// Lattti " 
       * +location.getLatitude()); 
       * System.out.println("getting location continous ////// LONGITU " 
       * + location.getLongitude()); 
       */ 
       manager.requestLocationUpdates(
         LocationManager.NETWORK_PROVIDER, 3000, 0, mylistener); 

      } else { 
       Toast.makeText(MyService.this, "Please oN Gps ", 
         Toast.LENGTH_LONG).show(); 
      } 
     } 

     @Override 
     protected Void doInBackground(Void... params) { 
      // TODO Auto-generated method stub 
      // getting current lattitude and longitude 

      return null; 
     }// method ends 
    }// asyntask class ends 

    void handleLocationChanged(Location loc) { 
     lattitude = loc.getLatitude(); 
     longitude = loc.getLongitude(); 
     /*Toast.makeText(MyService.this, 
       "lat is " + lattitude + " long is " + longitude, 
       Toast.LENGTH_LONG).show();*/ 
     System.out.println("getting location continous ////// Lattti " 
       + lattitude); 
     System.out.println("getting location continous ////// LONGITU " 
       + longitude); 

     generateNoteOnSD("GpsTesting.txt", "lattitude is" + lattitude + "\n" 
       + " longitude" + longitude); 

    } // method ends 

    public LocationListener mylistener = new LocationListener() { 

     @Override 
     public void onLocationChanged(Location loc) { 
      handleLocationChanged(loc); 
     } 

     public void onProviderDisabled(String arg0) { 
      // TODO Auto-generated method stub 
      // Toast.makeText(mContext, "Gps is disable", 
      // Toast.LENGTH_SHORT).show(); 
     } 

     public void onProviderEnabled(String arg0) { 
      // TODO Auto-generated method stub 
      // Toast.makeText(mContext, "Gps is on", Toast.LENGTH_SHORT).show(); 
     } 

     public void onStatusChanged(String arg0, int arg1, Bundle arg2) { 
      // TODO Auto-generated method stub 
      // Toast.makeText(appcontext, "Gps status is chnged ", 
      // Toast.LENGTH_SHORT).show(); 
     } 
    }; 

    public void showSettingsAlert() { 
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(
       MainActivity.getContextForService()); 

     // Setting Dialog Title 
     alertDialog.setTitle("Alert"); 

     // Setting Dialog Message 
     alertDialog 
       .setMessage("GPS is not enabled. Do you want to go to settings menu?"); 

     // On pressing Settings button 
     alertDialog.setPositiveButton("Settings", 
       new DialogInterface.OnClickListener() { 
        public void onClick(DialogInterface dialog, int which) { 
         Intent intent = new Intent(
           Settings.ACTION_LOCATION_SOURCE_SETTINGS); 
         getApplicationContext().startActivity(intent); 
        } 
       }); 

     // on pressing cancel button 
     alertDialog.setNegativeButton("Cancel", 
       new DialogInterface.OnClickListener() { 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.cancel(); 
        } 
       }); 

     // Showing Alert Message 
     alertDialog.show(); 
    }// method ends 
     // method for sending notiifcation 

    public void sendNotification() { 
     int MY_NOTIFICATION_ID = 1; 
     PendingIntent contentIntent = PendingIntent.getActivity(
       getApplicationContext(), 0, new Intent(MyService.this, 
         MainActivity.class), 0); 
     Notification myNotification = new NotificationCompat.Builder(
       getApplicationContext()) 
       .setContentTitle("Notification for Lat and Long") 
       .setContentText("hi testing notiifaction on lat and long") 
       .setTicker(" ToDoList Notification") 
       .setWhen(System.currentTimeMillis()) 
       .setContentIntent(contentIntent) 
       .setDefaults(Notification.DEFAULT_SOUND).setAutoCancel(true) 
       .setSmallIcon(R.drawable.ic_launcher).build(); 
     NotificationManager notificationManager = (NotificationManager) MainActivity 
       .getContextForService().getSystemService(
         Context.NOTIFICATION_SERVICE); 
     notificationManager.notify(MY_NOTIFICATION_ID, myNotification); 
    } // method ends 
     // writing file on 

    public void generateNoteOnSD(String sFileName, String sBody) { 
     try { 
      File root = new File(Environment.getExternalStorageDirectory() 
        + "/sdcard", "Gps_Data"); 
      if (!root.exists()) { 
       root.mkdirs(); 
      } 
      File gpxfile = new File(root, sFileName); 
      FileWriter writer = new FileWriter(gpxfile); 
      writer.append(sBody); 
      writer.flush(); 
      writer.close(); 

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

     } 
    } // method ends 

    private boolean haveNetworkConnection() { 
     boolean haveConnectedWifi = false; 
     boolean haveConnectedMobile = false; 

     ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 
     NetworkInfo[] netInfo = cm.getAllNetworkInfo(); 
     for (NetworkInfo ni : netInfo) { 
      if (ni.getTypeName().equalsIgnoreCase("WIFI")) 
       if (ni.isConnected()) 
        haveConnectedWifi = true; 
      if (ni.getTypeName().equalsIgnoreCase("MOBILE")) 
       if (ni.isConnected()) 
        haveConnectedMobile = true; 
     } 
     return haveConnectedWifi || haveConnectedMobile; 
    } 
} // final class ends