我创建了一个MapActivity将地图聚焦到用户位置的地图。
public void getMyLatLng() {
LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
LocationListener ll = new LocationListener() {
@Override
public void onStatusChanged(String provider, int status,
Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onLocationChanged(Location location) {
myLatLng = new LatLng(location.getLatitude(),location.getLongitude());
}
};
lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, ll);
lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
//myLatLng = new LatLng(myLoc.getLatitude(), myLoc.getLongitude());
}
java.lang.NullPointerException第一次运行时出现问题。但是，当我再次运行它时，它可以工作。第二个问题是，当我放置NETWORK_PROVIDER而不是GPS_PROVIDER时，它将很好地工作。有什么建议可以解决这个问题吗？
您可以从GPS和nework请求更新位置，例如：
public class LocationService implements LocationListener {
boolean isGPSEnabled = false;
boolean isNetworkEnabled = false;
boolean canGetLocation = false;
final static long MIN_TIME_INTERVAL = 60 * 1000L;
Location location;
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 0; // 10
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1; // 1 minute
protected LocationManager locationManager;
private CountDownTimer timer = new CountDownTimer(5 * 1000, 1000) {
public void onTick(long millisUntilFinished) {
}
public void onFinish() {
stopUsingGPS();
}
};
public LocationService() {
super(R.id.gps_service_id);
}
public void start() {
if (Utils.isNetworkAvailable(context)) {
try {
timer.start();
locationManager = (LocationManager) context
.getSystemService(Context.LOCATION_SERVICE);
isGPSEnabled = locationManager
.isProviderEnabled(LocationManager.GPS_PROVIDER);
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
this.canGetLocation = true;
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 tempLocation = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (tempLocation != null
&& isBetterLocation(tempLocation,
location))
location = tempLocation;
}
}
if (isGPSEnabled) {
locationManager.requestSingleUpdate(
LocationManager.GPS_PROVIDER, this, 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 tempLocation = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (tempLocation != null
&& isBetterLocation(tempLocation,
location))
location = tempLocation;
}
}
} catch (Exception e) {
onTaskError(e.getMessage());
e.printStackTrace();
}
} else {
onOfflineResponse(requestData);
}
}
public void stopUsingGPS() {
if (locationManager != null) {
locationManager.removeUpdates(LocationService.this);
}
}
public boolean canGetLocation() {
locationManager = (LocationManager) context
.getSystemService(Context.LOCATION_SERVICE);
isGPSEnabled = locationManager
.isProviderEnabled(LocationManager.GPS_PROVIDER);
// getting network status
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
return isGPSEnabled || isNetworkEnabled;
}
@Override
public void onLocationChanged(Location location) {
if (location != null
&& isBetterLocation(location, this.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 Object getResponseObject(Object location) {
return location;
}
public static boolean isBetterLocation(Location location,
Location currentBestLocation) {
if (currentBestLocation == null) {
// A new location is always better than no location
return true;
}
// Check whether the new location fix is newer or older
long timeDelta = location.getTime() - currentBestLocation.getTime();
boolean isSignificantlyNewer = timeDelta > MIN_TIME_INTERVAL;
boolean isSignificantlyOlder = timeDelta < -MIN_TIME_INTERVAL;
boolean isNewer = timeDelta > 0;
// If it's been more than two minutes since the current location,
// use the new location
// because the user has likely moved
if (isSignificantlyNewer) {
return true;
// If the new location is more than two minutes older, it must
// be worse
} else if (isSignificantlyOlder) {
return false;
}
// Check whether the new location fix is more or less accurate
int accuracyDelta = (int) (location.getAccuracy() - currentBestLocation
.getAccuracy());
boolean isLessAccurate = accuracyDelta > 0;
boolean isMoreAccurate = accuracyDelta < 0;
boolean isSignificantlyLessAccurate = accuracyDelta > 200;
// Check if the old and new location are from the same provider
boolean isFromSameProvider = isSameProvider(location.getProvider(),
currentBestLocation.getProvider());
// Determine location quality using a combination of timeliness and
// accuracy
if (isMoreAccurate) {
return true;
} else if (isNewer && !isLessAccurate) {
return true;
} else if (isNewer && !isSignificantlyLessAccurate
&& isFromSameProvider) {
return true;
}
return false;
}
}
请注意，每次获取位置时，我们都将其与已知位置进行比较，以通过调用isBetterLocation更好地找到该新位置。
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