getlastknownlocation（）返回null，应用程序正在关闭

即时尝试获取当前位置每隔几秒钟，我这样做与AlarmManager和LocationListener和位置管理器。在设置报警之前，我需要获取当前位置来计算一般距离。当我在AVD上运行我的应用程序并设置纬度&长时间手动与DDMS的应用程序工作正常，并做好这项工作。问题是当应用程序在真实设备上运行时，应用程序立即关闭（当我不手动设置位置时，它也会失败）。请问有什么问题？我只需要一个按钮被点击时，当前的位置和每个几秒钟......getlastknownlocation（）返回null，应用程序正在关闭

GPSTracker.Java：

public class GPSTracker extends Service implements LocationListener { 

private final Context mContext; 

// flag for GPS status 
boolean isGPSEnabled = false; 

// flag for network status 
boolean isNetworkEnabled = false; 

// flag for GPS status 
boolean canGetLocation = false; 

Location location; // location 
double latitude; // latitude 
double longitude; // longitude 

// The minimum distance to change Updates in meters 
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters 

// The minimum time between updates in milliseconds 
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute 

// Declaring a Location Manager 
protected LocationManager locationManager; 


public GPSTracker(Context context) { 
    this.mContext = context; 
    getLocation(); 
} 


public Location getLocation() { 
    try { 
     locationManager = (LocationManager) mContext 
       .getSystemService(LOCATION_SERVICE); 

     // getting GPS status 
     isGPSEnabled = locationManager 
       .isProviderEnabled(LocationManager.GPS_PROVIDER); 

     // getting network status 
     isNetworkEnabled = locationManager 
       .isProviderEnabled(LocationManager.NETWORK_PROVIDER); 

     if (!isGPSEnabled && !isNetworkEnabled) { 
      // no network provider is enabled 
     } else { 
      this.canGetLocation = true; 
      // First get location from Network Provider 
      if (isNetworkEnabled) { 
       if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 
        // TODO: Consider calling 
        // ActivityCompat#requestPermissions 
        // here to request the missing permissions, and then overriding 
        // public void onRequestPermissionsResult(int requestCode, String[] permissions, 
        //           int[] grantResults) 
        // to handle the case where the user grants the permission. See the documentation 
        // for ActivityCompat#requestPermissions for more details. 
        return location; 
       } 
       locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, MIN_TIME_BW_UPDATES, MIN_DISTANCE_CHANGE_FOR_UPDATES, this); 
       Log.d("Network", "Network"); 
       if (locationManager != null) { 
        location = 
        locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER); 
        if (location != null) { 
         latitude = location.getLatitude(); 
         longitude = location.getLongitude(); 
        } 
       } 
      } 
      // if GPS Enabled get lat/long using GPS Services 
      if (isGPSEnabled) { 
       if (location == null) { 
        locationManager.requestLocationUpdates(
          LocationManager.GPS_PROVIDER, 
          MIN_TIME_BW_UPDATES, 
          MIN_DISTANCE_CHANGE_FOR_UPDATES, this); 
        Log.d("GPS Enabled", "GPS Enabled"); 
        if (locationManager != null) { 
         location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
         if (location != null) { 
          latitude = location.getLatitude(); 
          longitude = location.getLongitude(); 
         } 
        } 
       } 
      } 
     } 

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

    return location; 
} 

/** 
* Stop using GPS listener 
* Calling this function will stop using GPS in your app 
* */ 
public void stopUsingGPS() { 
    if (locationManager != null) { 
     if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 
      // TODO: Consider calling 
      // ActivityCompat#requestPermissions 
      // here to request the missing permissions, and then overriding 
      // public void onRequestPermissionsResult(int requestCode, String[] permissions, 
      //           int[] grantResults) 
      // to handle the case where the user grants the permission. See the documentation 
      // for ActivityCompat#requestPermissions for more details. 
      return; 
     } 
     locationManager.removeUpdates(GPSTracker.this); 
     Log.d("GPS is stopped", "GPS is stopped"); 
    } 
} 

/** 
* Function to get latitude 
* */ 
public double getLatitude() { 
    if (location != null) { 
     latitude = location.getLatitude(); 
    } 

    // return latitude 
    return latitude; 
} 

/** 
* Function to get longitude 
* */ 
public double getLongitude() { 
    if (location != null) { 
     longitude = location.getLongitude(); 
    } 

    // return longitude 
    return longitude; 
} 

/** 
* Function to check GPS/wifi enabled 
* @return boolean 
* */ 
public boolean canGetLocation() { 
    return this.canGetLocation; 
} 

/** 
* Function to show settings alert dialog 
* On pressing Settings button will lauch Settings Options 
* */ 
public void showSettingsAlert() { 
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext); 

    // Setting Dialog Title 
    alertDialog.setTitle("GPS is settings"); 

    // 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); 
      mContext.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(); 
} 




@Override 
public void onLocationChanged(Location location) { 
} 

@Override 
public void onProviderDisabled(String provider) { 
} 

@Override 
public void onProviderEnabled(String provider) { 
} 

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

@Override 
public IBinder onBind(Intent arg0) { 
    return null; 
}

Alarm.Java：

@Override 
public void onReceive(Context context, Intent intent) { 

    /** PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE); 
    PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, ""); 
    wl.acquire();**/ 

    // Put here YOUR code. 
    //Intent i= new Intent(this,AlarmActivity.class); 
    //startActivity(i); 

    try { 


     gps = new GPSTracker(context); 
     double latitude = gps.getLatitude(); 
     double longitude = gps.getLongitude(); 

     Location CurrLoc = gps.getLocation(); 
     Location DistLoc = new Location("wow"); 
     DistLoc.setLatitude(32.159141); 
     DistLoc.setLongitude(34.922564); 
     float CurrDistance = CurrLoc.distanceTo(DistLoc); 

     SharedPreferences prefs = context.getSharedPreferences("AlarmDistanceAndUserStatus", Context.MODE_PRIVATE); 
     float AlarmDistance=prefs.getFloat("AlarmDistance",0); 


     Log.d("distance invoke alarmRe",String.valueOf(AlarmDistance)); 
     Log.d("current distance is:",String.valueOf(CurrDistance)); 

     // Log.d("Run once -2",String.valueOf(AlarmActivity.RUN_ONCE)); 
     // Log.d("distance invoke alarm-2",String.valueOf(AlarmActivity.AlarmDistance)); 
     if(CurrDistance>=0 && CurrDistance<=50){ 
      SharedPreferences.Editor editor=prefs.edit(); 
      editor.putBoolean("UserStatus",false); 
      editor.commit(); 
      this.CancelAlarm(context); 

      Bundle bundle = intent.getExtras(); 
      String message = bundle.getString("alarm_message"); 

      Intent newIntent = new Intent(context, AlarmActivity.class); 
      newIntent.putExtra("alarm_message", message); 
      newIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
      context.startActivity(newIntent); 
     } 
     else if(AlarmDistance>=CurrDistance){ 
      Bundle bundle = intent.getExtras(); 
      String message = bundle.getString("alarm_message"); 

      Intent newIntent = new Intent(context, AlarmActivity.class); 
      newIntent.putExtra("alarm_message", message); 
      newIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
      context.startActivity(newIntent); 
     } 


     Toast.makeText(context, "Your Location is - \nLat: " + latitude + "\nLong: " + longitude + " distanceto:" + CurrDistance + " from AlaramSet!!!", Toast.LENGTH_LONG).show(); 

     Log.d("onReceive", "onReceive"); 

    } catch (Exception e) { 
     Toast.makeText(context, "There was an error somewhere, but we still received an alarm", Toast.LENGTH_SHORT).show(); 
     e.printStackTrace(); 

    } 

    // Toast.makeText(context, "Alarm !!!!!!!!!!", Toast.LENGTH_LONG).show(); // For example 

    //wl.release(); 
} 


public void SetAlarm(Context context,int SecondsInterval) { 

    Calendar calendar = Calendar.getInstance(); 
    calendar.add(Calendar.SECOND, SecondsInterval); 
    AlarmManager am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE); 
    Intent i = new Intent(context, Alarm.class); 
    PendingIntent pi = PendingIntent.getBroadcast(context, 0, i, 0); 
    am.setInexactRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), (1000 * SecondsInterval), pi); // Millisec * Second * Minute 
    Toast.makeText(context, "Alarm Set!!!", Toast.LENGTH_LONG).show(); 

} 

public void CancelAlarm(Context context) { 

    Intent intent = new Intent(context, Alarm.class); 
    PendingIntent sender = PendingIntent.getBroadcast(context, 0, intent, 0); 
    AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE); 
    alarmManager.cancel(sender); 
    Toast.makeText(context, "Alarm Canceled!!!", Toast.LENGTH_LONG).show(); 
}

AlarmActivity.Java：

public class AlarmActivity extends AppCompatActivity public static boolean RUN_ONCE = true;

GPSTracker gps; 
Alarm alarm; 
SharedPreferences sharedpref; 
boolean UserStatus=true; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_alarm); 

    alarm = new Alarm(); 
    Log.d("Run once -2", String.valueOf(RUN_ONCE)); 
    runOnce(); 
    sharedpref=getSharedPreferences("AlarmDistanceAndUserStatus", Context.MODE_PRIVATE); 
    SharedPreferences.Editor editor=sharedpref.edit(); 
    UserStatus=sharedpref.getBoolean("UserStatus",true); 
    Log.d("UserStatus now is:", String.valueOf(UserStatus)); 
    if(UserStatus){ 
     Button OkStopButton=(Button)findViewById(R.id.OkStopButton); 
     OkStopButton.setVisibility(View.VISIBLE); 
     TextView WakeUpTimeTextView=(TextView)findViewById(R.id.WakeUpTimeTextView); 
     WakeUpTimeTextView.setVisibility(View.VISIBLE); 

     Button DidItButton=(Button)findViewById(R.id.DidItButton); 
     Button MissItButton=(Button)findViewById(R.id.MissItButton); 
     DidItButton.setVisibility(View.INVISIBLE); 
     MissItButton.setVisibility(View.INVISIBLE); 
     TextView DestArrivedTextView=(TextView)findViewById(R.id.DestArrivedTextView); 
     DestArrivedTextView.setVisibility(View.INVISIBLE); 
    } 
    else{ 
     Button OkStopButton=(Button)findViewById(R.id.OkStopButton); 
     OkStopButton.setVisibility(View.INVISIBLE); 
     TextView WakeUpTimeTextView=(TextView)findViewById(R.id.WakeUpTimeTextView); 
     WakeUpTimeTextView.setVisibility(View.INVISIBLE); 

     Button DidItButton=(Button)findViewById(R.id.DidItButton); 
     Button MissItButton=(Button)findViewById(R.id.MissItButton); 
     DidItButton.setVisibility(View.VISIBLE); 
     MissItButton.setVisibility(View.VISIBLE); 
     TextView DestArrivedTextView=(TextView)findViewById(R.id.DestArrivedTextView); 
     DestArrivedTextView.setVisibility(View.VISIBLE); 

    } 
} 

private void runOnce() { 
    if (RUN_ONCE) { 
     RUN_ONCE = false; 
     gps = new GPSTracker(AlarmActivity.this); 
     if (gps.canGetLocation) { 

      double latitude = gps.getLatitude(); 
      double longitude = gps.getLongitude(); 
      Location loc = gps.getLocation(); 
      Location dist = new Location("wow"); 
      dist.setLatitude(32.159058); 
      dist.setLongitude(34.922536); 
      float FirstDistance = loc.distanceTo(dist); 
      Log.d("first distance",String.valueOf(FirstDistance)); 

      //System.currentTimeMillis() 
      //interval time of distance check 
      int SecondsInterval; 
      if (FirstDistance >= 0 && FirstDistance <= 1000) SecondsInterval = 3; 
      else if (FirstDistance > 1000 && FirstDistance <= 2000) SecondsInterval = 4; 
      else if (FirstDistance > 2000 && FirstDistance <= 3500) SecondsInterval = 5; 
      else SecondsInterval = 8; 
      /// 
      //check the distance to alarm user before dist. station 
      int MissingCount = 2;//for example-import from db 

      float AlarmDistance= (FirstDistance/ 10) * MissingCount; 
      sharedpref=getSharedPreferences("AlarmDistanceAndUserStatus",Context.MODE_PRIVATE); 
      SharedPreferences.Editor editor=sharedpref.edit(); 
      editor.putFloat("AlarmDistance",AlarmDistance); 
      editor.putBoolean("UserStatus",true); 
      editor.commit(); 


      alarm.SetAlarm(this,SecondsInterval); 
      Intent newIntent = new Intent(this, MainActivity.class); 
      this.startActivity(newIntent); 
     } else { 
      gps.showSettingsAlert(); 
     } 


    } 
} 


public void StopOnClick(View v) { 

    // gps.stopUsingGPS(); 

    RUN_ONCE = true; 
    sharedpref=getSharedPreferences("AlarmDistanceAndUserStatus",Context.MODE_PRIVATE); 
    SharedPreferences.Editor editor=sharedpref.edit(); 
    editor.putFloat("AlarmDistance",0); 
    editor.putBoolean("UserStatus",true); 
    editor.commit(); 
    alarm.CancelAlarm(this); 
    //back to Home Page 
} 

public void DidItOnClick(View v){ 
    //Return to Home Page (e.g: MainActivity) 
    Intent newIntent = new Intent(this, MainActivity.class); 
    this.startActivity(newIntent); 


    RUN_ONCE = true; 
    sharedpref=getSharedPreferences("AlarmDistanceAndUserStatus",Context.MODE_PRIVATE); 
    SharedPreferences.Editor editor=sharedpref.edit(); 
    editor.putFloat("AlarmDistance",0); 
    editor.putBoolean("UserStatus", true); 
    editor.commit(); 
} 

public void MissItOnClick(View v){ 
    //go check altenative ways 


    RUN_ONCE = true; 
    sharedpref=getSharedPreferences("AlarmDistanceAndUserStatus",Context.MODE_PRIVATE); 
    SharedPreferences.Editor editor=sharedpref.edit(); 
    editor.putFloat("AlarmDistance",0); 
    editor.putBoolean("UserStatus",true); 
    editor.commit(); 
}

}

失败：

Unable to start activity ComponentInfo{com.example.liorozit.gpstest/com.example.liorozit.gpstest.AlarmActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'float android.location.Location.distanceTo(android.location.Location)' on a null object reference

有其通过意图移动到AlarmActivity类并调用它的外部类的OnCraete（）。我能做些什么请修复概率并得到我目前的位置？谢谢！

来源

2016-06-09 lior.g

如果你想在你的活动中获得位置，并且如果不需要在后台运行它，你可以试试这个。

package com.jmarkstar.activitylocation; 

import android.content.Context; 
import android.location.Criteria; 
import android.location.Location; 
import android.location.LocationListener; 
import android.location.LocationManager; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.widget.Toast; 

public class MainActivity extends AppCompatActivity { 

    private LocationManager locationManager; 
    private MyLocationListener locationListener; 
    private String latitude; 
    private String longitude; 

    @Override 
    protected void onStart() { 
     super.onStart(); 

     locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE); 
     locationListener = new MyLocationListener(); 
     Criteria criteria = new Criteria(); 
     criteria.setAltitudeRequired(false); 
     criteria.setBearingRequired(false); 
     criteria.setCostAllowed(false); 
     criteria.setPowerRequirement(Criteria.ACCURACY_FINE); 

     String bestEnabledProvider = locationManager.getBestProvider(criteria, true); 
     locationManager.requestLocationUpdates(bestEnabledProvider, 0, 0, locationListener); 
    } 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     //YOU CODE 
    } 

    private class MyLocationListener implements LocationListener { 

      @Override 
      public void onLocationChanged(Location location) { 
       makeUseOfNewLocation(location); 
       locationManager.removeUpdates(locationListener); 
      } 

      private void makeUseOfNewLocation(final Location location) { 
       if (location != null) { 
        String message = "position: " + location.getLatitude() + ", " + location.getLongitude() + " accuracy: " + location.getAccuracy(); 
        Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG).show(); 

        latitude = String.valueOf(location.getLatitude()); 
        longitude = String.valueOf(location.getLongitude()); 

        //YOUR CODE 
       } 
      } 

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

     @Override 
     public void onProviderEnabled(String provider) {} 

     @Override 
     public void onProviderDisabled(String provider) {} 
    } 
}

来源

2016-06-09 18:00:17 jmarkstar

感谢jmarkstar，那么我应该如何使用AlarmActivity类来获取当前位置？ –

我已经改变了答案，试试吧。 – jmarkstar

getlastknownlocation（）返回null，应用程序正在关闭

回答

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