问题
Followind code always return null poiner exception for location manager.
My GPSTracker class 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;
//Location locManager = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
public GPSTracker(Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation() {
try {
locationManager = (LocationManager) this.getSystemService(Context.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) {
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){
locationManager.removeUpdates(GPSTracker.this);
}
}
/**
* 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) {
this.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;
}
I am trying to call
if(gps.isGPSEnabled){
Toast.makeText(getBaseContext(),"GPS enabled",
Toast.LENGTH_SHORT).show();
baseurl = "http://my.careerfolio.net";
}
else{
gps.showSettingsAlert();
}
it always display settings alert rather then toast text, any help?
My Log.
06-20 02:54:06.336: W/System.err(909): java.lang.NullPointerException
06-20 02:54:06.416: W/System.err(909): at android.content.ContextWrapper.getSystemService(ContextWrapper.java:519)
06-20 02:54:06.416: W/System.err(909): at com.incv.mobile.freejscf.GPSTracker.getLocation(GPSTracker.java:50)
06-20 02:54:06.446: W/System.err(909): at com.incv.mobile.freejscf.GPSTracker.<init>(GPSTracker.java:44)
06-20 02:54:06.446: W/System.err(909): at com.incv.mobile.freejscf.MyApplication.<init>(MyApplication.java:34)
06-20 02:54:06.446: W/System.err(909): at java.lang.Class.newInstanceImpl(Native Method)
06-20 02:54:06.456: W/System.err(909): at java.lang.Class.newInstance(Class.java:1130)
06-20 02:54:06.486: W/System.err(909): at android.app.Instrumentation.newApplication(Instrumentation.java:990)
06-20 02:54:06.486: W/System.err(909): at android.app.Instrumentation.newApplication(Instrumentation.java:975)
06-20 02:54:06.486: W/System.err(909): at android.app.LoadedApk.makeApplication(LoadedApk.java:504)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4417)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread.access$1300(ActivityThread.java:141)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
06-20 02:54:06.506: W/System.err(909): at android.os.Handler.dispatchMessage(Handler.java:99)
06-20 02:54:06.506: W/System.err(909): at android.os.Looper.loop(Looper.java:137)
06-20 02:54:06.516: W/System.err(909): at android.app.ActivityThread.main(ActivityThread.java:5103)
06-20 02:54:06.516: W/System.err(909): at java.lang.reflect.Method.invokeNative(Native Method)
06-20 02:54:06.516: W/System.err(909): at java.lang.reflect.Method.invoke(Method.java:525)
06-20 02:54:06.546: W/System.err(909): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
06-20 02:54:06.546: W/System.err(909): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-20 02:54:06.546: W/System.err(909): at dalvik.system.NativeStart.main(Native Method)
回答1:
You are trying to getting location manager in Location class not in activity context.So change Location class instance this to activity's context mContext. so change this
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
to
locationManager = (LocationManager) mContext.getSystemService(Context.LOCATION_SERVICE);
Edit
If you are getting location using GPS you need to add ACCESS_FINE_LOCATION (Which includes both ACCESS_FINE_LOCATION and ACCESS_COARSE_LOCATION ). Also if you are getting network-based location then you need to add INTERNET permission too.
So,Open your AndroidManifest.xml file and do the following changes.
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
回答2:
locationManager = (LocationManager) mContext.getSystemService(Context.LOCATION_SERVICE);
In Same line how i set accuray high
回答3:
If you are in java class put not an activity use
LocationManager locationManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
来源：https://stackoverflow.com/questions/24320989/locationmanager-locationmanager-this-getsystemservicecontext-location-servi