Question

我在Android Dev Guid中阅读了有关Obtaining User Location的教程，我尝试将其改编为以下代码..但我不知道应该将哪个位置值放入isBetterLocation(Location location, Location currentBestLocation)

Example.class

       private LocationManager locman;

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

            String context = Context.LOCATION_SERVICE;
            locman = (LocationManager)getSystemService(context);

            Criteria criteria = new Criteria();
            criteria.setAccuracy(Criteria.ACCURACY_FINE);
            criteria.setAltitudeRequired(false);
            criteria.setBearingRequired(false);
            criteria.setPowerRequirement(Criteria.POWER_LOW);

            String provider = locman.getBestProvider(criteria, true);
            locman.requestLocationUpdates(
                    provider,MIN_TIME, MIN_DISTANCE, locationListener);

        }

        private LocationListener locationListener = new LocationListener(){

        @Override
        public void onLocationChanged(Location location) {
            // What should i pass as first and second parameter in this method
            if(isBetterLocation(location1,location2)){
               // isBetterLocation = true > do updateLocation 
               updateLocation(location);
            }
        }

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

       };

     protected boolean isBetterLocation(Location location, Location currentBestLocation) {
         if (currentBestLocation == null) {
            // A new location is always better than no location
            return true;
         }
          //Brief ... See code in Android Dev Guid "Obtaining User Location"
     }

Answer 1

真的不是那么难。代码的作用是接收到找到的位置的连续更新;您可以让多个听众收听不同的提供商，因此这些更新可能或多或少准确，具体取决于提供商（例如GPS可能比网络更准确）。 isBetterLocation(...)评估监听器找到的位置实际上是否比您已经知道的位置更好（并且应该在您的代码中引用）。 isBetterLocation（...）代码已有详细记录，因此不难理解，但第一个参数位置是提供程序找到的新位置， currentBestLocation 是您已经了解的位置。

我使用的代码与您的代码大致相同，但我不只是采用最佳提供商。处理程序的东西是因为我不想继续更新，只需在两分钟的最长时间内找到足够准确的最佳位置（GPS可能需要一点时间）。

private Location currentBestLocation = null;
private ServiceLocationListener gpsLocationListener;
private ServiceLocationListener networkLocationListener;
private ServiceLocationListener passiveLocationListener;
private LocationManager locationManager;

private Handler handler = new Handler();


public void fetchLocation() {
    locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

    try {
        LocationProvider gpsProvider = locationManager.getProvider(LocationManager.GPS_PROVIDER);
        LocationProvider networkProvider = locationManager.getProvider(LocationManager.NETWORK_PROVIDER);
        LocationProvider passiveProvider = locationManager.getProvider(LocationManager.PASSIVE_PROVIDER);

        //Figure out if we have a location somewhere that we can use as a current best location
        if( gpsProvider != null ) {
            Location lastKnownGPSLocation = locationManager.getLastKnownLocation(gpsProvider.getName());
            if( isBetterLocation(lastKnownGPSLocation, currentBestLocation) )
                currentBestLocation = lastKnownGPSLocation;
        }

        if( networkProvider != null ) {
            Location lastKnownNetworkLocation = locationManager.getLastKnownLocation(networkProvider.getName());
            if( isBetterLocation(lastKnownNetworkLocation, currentBestLocation) )
                currentBestLocation = lastKnownNetworkLocation;
        }

        if( passiveProvider != null) {
            Location lastKnownPassiveLocation = locationManager.getLastKnownLocation(passiveProvider.getName());
            if( isBetterLocation(lastKnownPassiveLocation, currentBestLocation)) {
                currentBestLocation = lastKnownPassiveLocation;
            }
        }

        gpsLocationListener = new ServiceLocationListener();
        networkLocationListener = new ServiceLocationListener();
        passiveLocationListener = new ServiceLocationListener();

        if(gpsProvider != null) {
            locationManager.requestLocationUpdates(gpsProvider.getName(), 0l, 0.0f, gpsLocationListener);
        }

        if(networkProvider != null) {
            locationManager.requestLocationUpdates(networkProvider.getName(), 0l, 0.0f, networkLocationListener);
        }

        if(passiveProvider != null) {
            locationManager.requestLocationUpdates(passiveProvider.getName(), 0l, 0.0f, passiveLocationListener);
        }

        if(gpsProvider != null || networkProvider != null || passiveProvider != null) {
            handler.postDelayed(timerRunnable, 2 * 60 * 1000);
        } else {
            handler.post(timerRunnable);
        }
    } catch (SecurityException se) {
        finish();
    }
}

private class ServiceLocationListener implements android.location.LocationListener {

    @Override
    public void onLocationChanged(Location newLocation) {
        synchronized ( this ) {
            if(isBetterLocation(newLocation, currentBestLocation)) {
                currentBestLocation = newLocation;

                if(currentBestLocation.hasAccuracy() && currentBestLocation.getAccuracy() <= 100) {
                    finish();
                }
            }
        }
    }

    @Override
    public void onStatusChanged(String s, int i, Bundle bundle) {}

    @Override
    public void onProviderEnabled(String s) {}

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

private synchronized void finish() {
    handler.removeCallbacks(timerRunnable);
    handler.post(timerRunnable);
}

/** Determines whether one Location reading is better than the current Location fix
 * @param location  The new Location that you want to evaluate
 * @param currentBestLocation  The current Location fix, to which you want to compare the new one
 */
protected boolean isBetterLocation(Location location, Location currentBestLocation) {
    //etc
}

private Runnable timerRunnable = new Runnable() {

    @Override
    public void run() {
        Intent intent = new Intent(LocationService.this.getPackageName() + ".action.LOCATION_FOUND");

        if(currentBestLocation != null) {
            intent.putExtra(LocationManager.KEY_LOCATION_CHANGED, currentBestLocation);

            locationManager.removeUpdates(gpsLocationListener);
            locationManager.removeUpdates(networkLocationListener);
            locationManager.removeUpdates(passiveLocationListener);
        }
    }
};

location和currentBestLocation来自哪里？在Android开发指南（获取用户位置）

1 个答案: