我担心在主线程上找到位置信息（使用反向地理编码）会减慢我的UI。为了解决这个问题，我将信息放入AsyncTask（下面的代码）中，现在我想添加位置侦听器，但遇到了各种各样的问题。
我已经做了一些研究，现在想知道...是否甚至需要将位置代码放入AsyncTask中？也许Android只是“自然地”异步找到位置信息？
public class LocationAsyncTask extends AsyncTask<Void, String, String> {
@Override protected void onPostExecute(String result) {
// TODO Auto-generated method stub
tvLocation.setText(result);
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
tvLocation.setText("Finding current location");
}
@Override
protected String doInBackground(Void... params) {
// TODO Auto-generated method stub
LocationManager locationManager;
String context = Context.LOCATION_SERVICE;
locationManager = (LocationManager)getSystemService(context);
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);
Location location =locationManager.getLastKnownLocation(provider);
String strUpdateResult = updateWithANewLocation(location);
//locationManager.requestLocationUpdates(provider, 1000, 10, locationListener);
return strUpdateResult;
}
private String updateWithANewLocation(Location location) {
// TODO Auto-generated method stub
StringBuilder sbLocation = new StringBuilder();
String strLocation = new String();
TextView myLocationText;
String addressString = "No address found";
String latLongString = "";
//If there is a location
if (location!= null) {
double latitude = location.getLatitude();
double longitude = location.getLongitude();
double altitude = location.getAltitude();
float accuracy = location.getAccuracy();
float bearing = location.getBearing();
long time = location.getTime();
float speed = location.getSpeed();
String prov = location.getProvider();
strLocation = "Latitude: " + latitude + "\nLongitude: " + longitude + "\n" ;
publishProgress(strLocation);
Geocoder gc = new Geocoder(LateRunner.this, Locale.getDefault());
try {
List<Address> addresses = gc.getFromLocation(latitude, longitude, 1);
//if location and then address is found
if (addresses.size() > 0 ) {
Address address = addresses.get(0);
for (int i=0; i <address.getMaxAddressLineIndex(); i++) {
sbLocation.append(address.getAddressLine(i)).append("\n");
}
strLocation= sbLocation.toString();
publishProgress(strLocation);
}
//if location but no address
else {
strLocation = "Latitude: " + latitude + "\nLongitude: " + longitude + "\n";
publishProgress(strLocation);
} //end try
} catch (IOException e) {
strLocation = "Latitude: " + latitude + "\nLongitude: " + longitude + "\n";
publishProgress(strLocation);
}//end catch
}
//If no location found
else {
strLocation = "Unable to find location. ";
publishProgress(strLocation);
}
return strLocation;
}// end updateWithANewLocation()
@Override protected void onProgressUpdate(String... result) {
// TODO Auto-generated method stub
tvLocation.setText(result[0]);
}
}
最佳答案
我进行了一些快速搜索，没有看到对运行异步的LocationManager的任何特定引用，但我的假设是它是系统服务，因此以不影响UI性能的方式进行调度。
根据经验，我在获取主线程上的位置并将其显示给用户时没有问题。实际上，我计算出列表中约100个项目的距离，而UI却没有明显的下降。不过，我要说的是后者，您应该考虑AsyncTask，因为它很容易影响性能。尽管也要注意AsyncTask任务的时间和LocationManager位置的更新间隔。
根据每次对updateWithANewLocation的调用花费的时间，您可能需要考虑将其放在后台任务上，并将LocationManager保留在Main线程上。
我假设您遇到的问题是LocationManager上的事件处理。以下内容应使您对该问题的一部分有所了解：
http://developer.android.com/reference/android/location/LocationManager.html#requestLocationUpdates%28java.lang.String,%20long,%20float,%20android.location.LocationListener%29
调用线程必须是Looper
线程，例如主线程
调用Activity。
http://developer.android.com/reference/android/os/Looper.html
基本上，当您的LocationAsyncTask完成执行后，它消失了，因此事件回调发生在不再存在的线程上。 Looper将启动消息循环以接受那些LocationManager事件。