Excerpt from DeliveryDispatcher

MyLocationFinder.java

/**
 * Begins the search to find the device's location. When it finishes or times out,
 * it will invoke onLocationFound(Location) on all OnLocationFoundListeners
 * in mLocationFoundListeners. If a listener cancels its request for a Location,
 * but there are still others waiting, the search will continue.
 *
 * @param timeoutMillis The amount of time, in milliseconds,
 *                      that we should search for a location
 * @return True if we were able to include listener in a new or existing search, or false
 * if we were unable to begin searching or if listener was already listening
 */
public static boolean beginFindLocation(long timeoutMillis, OnLocationFoundListener listener)
{
    mLock.lock();

    boolean listenerSatisfied = false;

    Log.d(LOG_TAG, "Somebody wants to know our location...");

    // If we are already in the middle of a search, simply add listener to our list.
    // It will later be notified once our ongoing search is complete.
    if(mIsSearching)
    {
        if(addListener(listener))
        {
            Log.d(LOG_TAG, "Added listener to the list.");
            listenerSatisfied = true;
        }
        else
        {
            Log.d(LOG_TAG, "Listener was already listening!");
        }
    }
    else
    {
        // We were not searching, so start a new search.
        Log.d(LOG_TAG, "Beginning find location...");
        if(isLocationServicesAvailable())
        {
            // As long as Location Services are available, we can check
            // to see which location providers are available for use.
            boolean networkIsAvailable = mLocationManager.isProviderEnabled(
                    LocationManager.NETWORK_PROVIDER);
            boolean passiveIsAvailable = mLocationManager.isProviderEnabled(
                    LocationManager.PASSIVE_PROVIDER);
            boolean gpsIsAvailable = mLocationManager.isProviderEnabled(
                    LocationManager.GPS_PROVIDER);

            String available = networkIsAvailable ? "available" : "not available";
            Log.d(LOG_TAG, "Network provider is " + available + ".");
            available = passiveIsAvailable ? "available" : "not available";
            Log.d(LOG_TAG, "Passive provider is " + available + ".");
            available = gpsIsAvailable ? "available" : "not available";
            Log.d(LOG_TAG, "GPS provider is " + available + ".");

            // We can begin the search if any provider is available
            if(networkIsAvailable || passiveIsAvailable || gpsIsAvailable)
            {
                // Add listener as the first listener in our list
                addListener(listener);

                // Begin the search by subscribing to location updates

                // LocationManager.requestLocationUpdates() takes three parameters:
                // 1: the provider
                // 2: how often you want to receive updates (millis)
                // 3: minimum required change in distance to require an update (meters)
                // 4: a LocationListener

                Log.d(LOG_TAG, "Attaching to location updates...");
                // Attach to location updates from the best provider
                // Prefer network over passive and passive over gps
                if(networkIsAvailable)
                {
                    Log.d(LOG_TAG, "Using Network provider.");
                    mLocationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER, 0, 0, mLocationChangedListener);
                }
                else if (passiveIsAvailable)
                {
                    Log.d(LOG_TAG, "Using Passive provider.");
                    mLocationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER, 0, 0, mLocationChangedListener);
                }
                else if (gpsIsAvailable)
                {
                    Log.d(LOG_TAG, "Using GPS provider.");
                    mLocationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER, 0, 0, mLocationChangedListener);
                }

                // Start the timeout timer
                mStopTimer = new Timer();
                mStopTimer.schedule(new TimerTask()
                {
                    @Override
                    public void run()
                    {
                        // Stop searching after timeoutMillis, regardless of
                        // whether or not we have found the location
                        Log.d(LOG_TAG, "Search timed out!");
                        mLock.requestEndFindLocation(null);
                    }
                }, timeoutMillis);

                mIsSearching = true;
                listenerSatisfied = true;
            }
            else
            {
                // No location provider available
                Log.w(LOG_TAG, "Unable to begin finding location: " +
                        "No location provider available.");
            }
        }
        else
        {
            // Location Services unavailable
            Log.w(LOG_TAG, "Unable to begin finding location: " +
                    "Location Services are unavailable.");
        }
    }

    mLock.unlock();
    return listenerSatisfied;
}