Android下定位开发

首先来看一段Android开发文档中提供的有关定位开发的介绍：

Location and maps-based applications are compelling for mobile device users. You can build these capabilities into your applications using the classes of theandroid.location package and the Google Maps external library. The sections below provide details.

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Location Services

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Android gives your applications access to the location services supported by the device through the classes in the android.location package. The central component of the location framework is the LocationManager system service, which provides APIs to determine location and bearing of the underlying device (if available).

As with other system services, you do not instantiate a LocationManager directly. Rather, you request an instance from the system by callinggetSystemService(Context.LOCATION_SERVICE). The method returns a handle to a new LocationManager instance.

Once your application has a LocationManager, your application is able to do three things:

• Query for the list of all LocationProviders for the last known user location.
• Register/unregister for periodic updates of the user's current location from a location provider (specified either by criteria or name).
• Register/unregister for a given Intent to be fired if the device comes within a given proximity (specified by radius in meters) of a given lat/long.

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Requesting Location Updates

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Before addressing some of the location errors described above, here is an introduction to how you can obtain user location on Android.

Getting user location in Android works by means of callback. You indicate that you'd like to receive location updates from the LocationManager ("Location Manager") by calling requestLocationUpdates(), passing it a LocationListener. Your LocationListener must implement several callback methods that the Location Manager calls when the user location changes or when the status of the service changes.

For example, the following code shows how to define a LocationListener and request location updates:

// Acquire a reference to the system Location ManagerLocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);// Define a listener that responds to location updatesLocationListener locationListener = new LocationListener() {    public void onLocationChanged(Location location) {      // Called when a new location is found by the network location provider.      makeUseOfNewLocation(location);    }    public void onStatusChanged(String provider, int status, Bundle extras) {}    public void onProviderEnabled(String provider) {}    public void onProviderDisabled(String provider) {}  };// Register the listener with the Location Manager to receive location updateslocationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);

The first parameter in requestLocationUpdates() is the type of location provider to use (in this case, the Network Location Provider for cell tower and Wi-Fi based location). You can control the frequency at which your listener receives updates with the second and third parameter—the second is the minimum time interval between notifications and the third is the minimum change in distance between notifications—setting both to zero requests location notifications as frequently as possible. The last parameter is your LocationListener, which receives callbacks for location updates.

To request location updates from the GPS provider, substitute GPS_PROVIDER for NETWORK_PROVIDER. You can also request location updates from both the GPS and the Network Location Provider by calling requestLocationUpdates() twice—once for NETWORK_PROVIDER and once for GPS_PROVIDER.

Requesting User Permissions

In order to receive location updates from NETWORK_PROVIDER or GPS_PROVIDER, you must request user permission by declaring either the ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION permission, respectively, in your Android manifest file. For example:

<manifest ... >    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />    ...</manifest>

Without these permissions, your application will fail at runtime when requesting location updates.

Note: If you are using both NETWORK_PROVIDER and GPS_PROVIDER, then you need to request only the ACCESS_FINE_LOCATION permission, because it includes permission for both providers. (Permission forACCESS_COARSE_LOCATION includes permission only for NETWORK_PROVIDER.)