Bearbeiten von „Android Location API“

== Links und Quellen ==
http://www.vogella.com/articles/AndroidLocationAPI/article.html

== Position bestimmen ==
Android kann die Position mit dem GPS Empfänger, über umgebende WLAN Netzwerke (die dann Online mit einer Google Datenbank abgeglichen werden) oder über die aktuelle Handyzelle bestimmen.

Für die Positionsbestimmung stellt Android das Package:
 android.location
zur Verfügung. 

=== Wichtige Komponenten ===
==== Location Manager ====
''Class LocationManager'' für Zugriff auf Android location service
====LocationProvider====
Superclass für die LocationProvider die die Position liefern. Es gibt 3:
 network //Mobile oder WiFi
 gps
 passive // für externe Geräte
====LocationListener====
Über den Location Manager kann man einen LocationListener registrieren um regelmäßige Positionsupdates zu bekommen.

Hinweis in Stackoverflow wird über Probleme mit dem onStatusChanged Listener auf diversen Versionen von Android s.u.

==== Geocoder ====
Über die Geocoder Klasse kann man Positionsdaten zu Adressdaten und umgekehrt ermitteln (Google Service)
==== Notwendige Rechte / Permissions ====
ACCESS_FINE_LOCATION permission für GPS, ansonsten ACCESS_COARSE_LOCATION permission
=== Beispiel 1 - locationapi.simple ===
[[Android Location API - Simple Location]]


=== Location Snippets ===
==== User zum aktivieren von GPS auffordern ====
Hinweis: Es ist nicht möglich GPS nur über den Code zu starten. 
<pre>
LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
boolean enabled = service
  .isProviderEnabled(LocationManager.GPS_PROVIDER);

// Check if enabled and if not send user to the GSP settings
// Better solution would be to display a dialog (AlarmDialog) and suggesting to 
// go to the settings
if (!enabled) {
  Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
  startActivity(intent);
} 
</pre>
=== Simulation auf dem Simulator ===
Auf dem Emulierten Device GoogleMaps aktivieren falls das aktivieren des GPS Simulators nicht klappt (Bugs). Man kann die DDMS Perspective von Eclipse nehmen um Geopositionen zu senden.

 Window > Open Perspective > Other > DDMS

Über das Terinal und Telnet kann man auch Positionen schicken
 telnet localhost 5554
 geo fix 13.12 49.23

=== Probleme bei der Positionsabfrage umgehen ===
Quelle: http://stackoverflow.com/questions/2021176/how-can-i-check-the-current-status-of-the-gps-receiver

onStatusChanged() doesn't get called on Eclair and Froyo. It does get called on 1.6 though.
Simply counting all available satellites is, of course, useless.
Checking if any of the satellites returns true for usedInFix() isn't very helpful also. The system apparently loses the fix but still continue to report that there are several sats that are used in it.
So, the only working solution we have, and the one we actually use in our application, is the following. Let's say we have this simple class that implements the GpsStatus.Listener:
<pre>
private class MyGPSListener implements GpsStatus.Listener {
    public void onGpsStatusChanged(int event) {
        switch (event) {
            case GpsStatus.GPS_EVENT_SATELLITE_STATUS:
                if (mLastLocation != null)
                    isGPSFix = (SystemClock.elapsedRealtime() - mLastLocationMillis) < 3000;

                if (isGPSFix) { // A fix has been acquired.
                    // Do something.
                } else { // The fix has been lost.
                    // Do something.
                }

                break;
            case GpsStatus.GPS_EVENT_FIRST_FIX:
                // Do something.
                isGPSFix = true;

                break;
        }
    }
}
</pre>
OK, now in onLocationChanged() you should add the following:

<pre>
@Override
public void onLocationChanged(Location location) {
    if (location == null) return;

    mLastLocationMillis = SystemClock.elapsedRealtime();

    // Do something.

    mLastLocation = location;
}
</pre>
And that's it. Basically, this is the line that does it all:

 isGPSFix = (SystemClock.elapsedRealtime() - mLastLocationMillis) < 3000;

You can tweak the milliseconds value of course, but I would suggest to set it around 3-5 seconds.

This actually works and though I haven't seen the source code that implements the standard GPS icon, this comes close to replicating its behavior. It could even outdo it lol. Hope this helps someone.