android - 是否有必要在单独的线程中查找获取位置？

Question

我担心在主线程上查找位置信息(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) 现在我想添加位置监听器，我遇到了各种各样的问题。

我做了一些研究，现在想知道...是否有必要将位置代码放入 AsyncTask 中？也许 Android 只是“自然地”异步查找位置信息？

  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]);
            } 
        }

Answer 1

我进行了一些快速搜索，但没有看到任何对异步运行的 LocationManager 的具体引用，但我的假设是它确实如此或以不影响 UI 性能的方式安排，因为它是一项系统服务。

根据经验，我可以毫无问题地获取主线程上的位置并将其显示回用户。事实上，我计算了列表中大约 100 个项目的距离，而 UI 没有明显变慢。后一种计算虽然是我认为您应该考虑 AsyncTask 的地方，因为它很容易影响性能。尽管还要注意 AsyncTask 任务的时长和 LocationManager 位置更新的更新间隔。

根据每次调用 updateWithANewLocation 所花费的时间，您可能需要考虑将其置于后台任务中并将 LocationManager 留在主线程中。

我假设您遇到问题的地方是 LocationManager 上的事件处理。以下内容应该可以让您深入了解问题的这一部分:

http://developer.android.com/reference/android/location/LocationManager.html#requestLocationUpdates%28java.lang.String,%20long,%20float,%20android.location.LocationListener%29

The calling thread must be a Looper thread such as the main thread of the calling Activity.

http://developer.android.com/reference/android/os/Looper.html

基本上，当您的 LocationAsyncTask 完成执行时，它就消失了，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。