GPS在Android的使用

GPS的开发、使用，有两个关键点：

1. 选择并激活合适的Provider；

2. 建立合理刷新机制。

下面是通用的方法，以“选择并激活合适的Provider”：

protectedvoidgetAndTraceLocation(){
//geocoder=newGeocoder(this,Locale.getDefault());;
geocoder=newGeocoder(this,Locale.ENGLISH);;
//AcquireareferencetothesystemLocationManager
locationManager=(LocationManager)this.getSystemService(Context.LOCATION_SERVICE);

Criteriacriteria=newCriteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
criteria.setAltitudeRequired(false);
criteria.setBearingRequired(false);
criteria.setCostAllowed(true);
criteria.setPowerRequirement(Criteria.POWER_LOW);

Stringprovider=locationManager.getBestProvider(criteria,true);
if(provider!=null){
Log.i(TAG,"GPSproviderisenabled:"+provider.toString());
//Getthelocation
latestLocation=locationManager.getLastKnownLocation(provider);
updateWithNewLocation(latestLocation);

//RegisterthelistenerwiththeLocationManagertoreceivelocation
locationManager.requestLocationUpdates(provider,1000,5,locationListener);
}else{
Log.i(TAG,"NoGPSproviderfound!");
updateWithNewLocation(null);
}
}

protected void getAndTraceLocation(){
		//geocoder = new Geocoder(this, Locale.getDefault());;
		geocoder = new Geocoder(this, Locale.ENGLISH);;
		// Acquire a reference to the system Location Manager
		locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

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

		String provider = locationManager.getBestProvider(criteria, true);
		if(provider!=null){
			Log.i(TAG, "GPS provider is enabled:" + provider.toString());
			// Get the location
			latestLocation = locationManager.getLastKnownLocation(provider);
			updateWithNewLocation(latestLocation);
	
			// Register the listener with the Location Manager to receive location
			locationManager.requestLocationUpdates(provider, 1000, 5, locationListener);
		}else{
			Log.i(TAG, "No GPS provider found!");
			updateWithNewLocation(null);
		}
	}

protectedfinalLocationListenerlocationListener=newLocationListener(){
publicvoidonLocationChanged(Locationlocation){
Log.i(TAG,"locationchangedto:"+location);
updateWithNewLocation(location);
}
publicvoidonProviderDisabled(Stringprovider){}
publicvoidonProviderEnabled(Stringprovider){}
publicvoidonStatusChanged(Stringprovider,intstatus,Bundleextras){}
};

	protected final LocationListener locationListener = new LocationListener() {
		public void onLocationChanged(Location location) {
			Log.i(TAG, "location changed to: " + location);
			updateWithNewLocation(location);
		}
		public void onProviderDisabled(String provider) {}
		public void onProviderEnabled(String provider) {}
		public void onStatusChanged(String provider, int status, Bundle extras) {}
	};

需要注意的是：

这里的locationManager.getBestProvider(criteria, true) 之后，必须进行是否为null的判断，否则在终端禁用GPS和网络以后会出现NPE异常。

注意这里回调了一个通用的updateWithNewLocation(latestLocation)方法，用户只要实现这个方法，即可实现第二个关键点，即“建立合理刷新机制”。

下面是最简单的例子：

@Override
protectedvoidupdateWithNewLocation(Locationlocation){
super.updateWithNewLocation(location);

Stringlocation_msg=context.getString(R.string.msg_no_gps);
if(location!=null){
location_msg=location.getLatitude()+","+location.getLongitude();
Log.i(TAG,location_msg);
}else{
Log.i(TAG,location_msg);
}

location_msg=String.format(_location_msg,location_msg);
_location.setText(location_msg);
}

@Override
protected void updateWithNewLocation(Location location) {
    	super.updateWithNewLocation(location);
    	
		String location_msg = context.getString(R.string.msg_no_gps);
		if (location != null) {
			location_msg = location.getLatitude() + "," + location.getLongitude();			
			Log.i(TAG, location_msg);
		} else {
			Log.i(TAG, location_msg);
		}
		
		location_msg = String.format(_location_msg, location_msg);
		_location.setText(location_msg);
	}