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”：

Java代码

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 ManagerlocationManager = (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 locationlatestLocation = locationManager.getLastKnownLocation(provider);updateWithNewLocation(latestLocation);// Register the listener with the Location Manager to receive locationlocationManager.requestLocationUpdates(provider, 1000, 5, locationListener);}else{Log.i(TAG, "No GPS provider found!");updateWithNewLocation(null);}}

Java代码

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：

Java代码

@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);
}

@Overrideprotected 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);}

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