使用异步任务获取当前位置

Question

我尝试使用异步任务获取当前位置，此代码在没有异步任务的情况下可以正常工作，但是当我尝试使用异步任务时，它显示未找到位置和抱歉未找到地址。这是我的代码，请帮助我提前感谢

public class MainActivity extends Activity {
/** Called when the activity is first created. */
String addressString;    
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
        new Getlocation().execute();    

}

// 开始异步任务

class Getlocation extends AsyncTask<String, String, String> {


    ProgressDialog p;

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub

       p = new ProgressDialog(MainActivity.this);                   
         p.setMessage("Please Wait Retrieving data..");     
         p.setTitle(" ");                                       
         p.setIcon(R.drawable.settings2);                       
         p.show();                                               
    }
    @Override
    protected String doInBackground(String... params) {
        Looper.prepare();

          LocationManager locationManager; 

            String context = Context.LOCATION_SERVICE; 
            locationManager = (LocationManager)getSystemService(context); 

            Criteria crta = new Criteria(); 
            crta.setAccuracy(Criteria.ACCURACY_FINE); 
            crta.setAltitudeRequired(false); 
            crta.setBearingRequired(false); 
            crta.setCostAllowed(true); 
            crta.setPowerRequirement(Criteria.POWER_LOW); 
            String provider = locationManager.getBestProvider(crta, true); 

         //String provider = LocationManager.GPS_PROVIDER; 
            Location location = locationManager.getLastKnownLocation(provider); 
            updateWithNewLocation(location); 
           LocationListener locationListener = new LocationListener() 
         { 

         @Override 
         public void onLocationChanged(Location location) { 
         updateWithNewLocation(location); 
         } 

         @Override 
         public void onProviderDisabled(String provider) { 
         updateWithNewLocation(null); 
         } 

         @Override 
         public void onProviderEnabled(String provider) { 
         } 

         @Override 
         public void onStatusChanged(String provider, int status, Bundle extras) { 
         } 

         };
         locationManager.requestLocationUpdates(provider, 2000, 10, locationListener); 
         Looper.loop();

        return addressString;
    }
     @Override
        protected void onPostExecute(String result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result); 
            p.dismiss();                    

    }   }
 private void updateWithNewLocation(Location location) { 
     String latLong;
     TextView myLocation; 
      addressString = "Sorry  No Address Found"; 
     if(location!=null) { 
    double lat = location.getLatitude(); 
     double lon = location.getLongitude(); 
     latLong = "Lat:" + lat + "\nLong:" + lon; 
     double lattitude = location.getLatitude(); 
     double longitude = location.getLongitude(); 
     Geocoder gc = new Geocoder(this,Locale.getDefault()); 
     try { 
     List<Address> addresses= gc.getFromLocation(lattitude, longitude, 1); 
     StringBuilder sb = new StringBuilder(); 
     if(addresses.size()>0) { 
     Address address=addresses.get(0);
     for(int i=0;i<address.getMaxAddressLineIndex();i++)
     sb.append(address.getAddressLine(i)).append("\n");
     sb.append(address.getLocality()).append("\n"); 
     sb.append(address.getPostalCode()).append("\n"); 
     sb.append(address.getCountryName()); 

     } 
     addressString = sb.toString(); 
     } 
     catch (Exception e) { 
     } 
     } else { 
     latLong = " NO Location Found "; 
     } 
Toast.makeText(getApplicationContext(), "Current Position is :\n"+ latLong + "\n"+  addressString ,Toast.LENGTH_LONG).show();
  //  myLocation.setText("Current Position is :\n"+ latLong + "\n"+  addressString ); 
        }

}

//这是我的日志

    10-01 22:34:13.720: E/WindowManager(2868): Activity com.example.sc.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@411dd3c8 that was originally added here
10-01 22:34:13.720: E/WindowManager(2868): android.view.WindowLeaked: Activity com.example.sc.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@411dd3c8 that was originally added here
10-01 22:34:13.720: E/WindowManager(2868):  at android.view.ViewRootImpl.<init>(ViewRootImpl.java:374)
10-01 22:34:13.720: E/WindowManager(2868):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:292)
10-01 22:34:13.720: E/WindowManager(2868):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:224)
10-01 22:34:13.720: E/WindowManager(2868):  at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:149)
10-01 22:34:13.720: E/WindowManager(2868):  at android.view.Window$LocalWindowManager.addView(Window.java:547)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.Dialog.show(Dialog.java:277)
10-01 22:34:13.720: E/WindowManager(2868):  at com.example.sc.MainActivity$Getlocation.onPreExecute(MainActivity.java:68)
10-01 22:34:13.720: E/WindowManager(2868):  at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
10-01 22:34:13.720: E/WindowManager(2868):  at android.os.AsyncTask.execute(AsyncTask.java:534)
10-01 22:34:13.720: E/WindowManager(2868):  at com.example.sc.MainActivity.onCreate(MainActivity.java:51)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.Activity.performCreate(Activity.java:5008)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-01 22:34:13.720: E/WindowManager(2868):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-01 22:34:13.720: E/WindowManager(2868):  at android.os.Looper.loop(Looper.java:137)
10-01 22:34:13.720: E/WindowManager(2868):  at android.app.ActivityThread.main(ActivityThread.java:4745)
10-01 22:34:13.720: E/WindowManager(2868):  at java.lang.reflect.Method.invokeNative(Native Method)
10-01 22:34:13.720: E/WindowManager(2868):  at java.lang.reflect.Method.invoke(Method.java:511)
10-01 22:34:13.720: E/WindowManager(2868):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-01 22:34:13.720: E/WindowManager(2868):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-01 22:34:13.720: E/WindowManager(2868):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

这看起来像经典的“在非Looper 线程中创建处理程序”异常。基本上，您正在创建一个 Handler 来接收位置消息到您的 LocationListener 对象，该对象是在它自己的线程中创建的。一旦方法返回，运行doInBackground() 的线程就会死掉。因此，LocationManager 正在向死线程中的死对象发送数据，您会得到一个异常。

Loopers 的一个很好的示例在这里：

What is the purpose of Looper and how to use it?

如果将Looper.prepare() 放在doInBackground() 的顶部，将Looper.loop() 放在底部，则可以继续使用AsyncTask。 Looper.loop() 只是一个空的 while 循环，它将让你的线程永远打开。

为了让它死掉，你必须在你的线程中调用 Looper.myLooper().quit() 来杀死它。最简单的方法是在Looper.prepare()之后立即执行，保存Looper 通过调用 Looper.myLoop()。然后在要停止更新时调用的方法中将其杀死。

class LooperAsyncTask extends AsyncTask<Void, Void, Void> {

    private mThreadLooper;

    @Override
    protected String doInBackground(String... params) {
      Looper.prepare();
      mThreadLooper = Looper.myLooper();
      **setup code**
      Looper.loop();
    }

    public void stopUpdates() {
      **cleanup code**
      if(mThreadLooper != null)
        mThreadLooper.quit();
    }
}

Answer 2

您的 LocationManager 和 LocationListener 不需要在 AsyncTask 中。它们应该在 Activity 中（如果您想在 Activity 之间共享它们，则应该在 Activity 引用的其他类中）。

在 AsyncTask 中注册 LocationListener 不是正确的方法，因为该侦听器与 AsyncTask 一起死亡，因此不会在附近侦听更新。

顺便说一句，您的 updateWithNewLocation() 方法正在创建一个它没有使用的 TextView。

通过在 updateWithNewLocation() 中调用 Toast，您实际上是在 doInBackground 中调用它，它不在 UI 线程上运行，因此 Toast 设置起来会很时髦，除非您在实例化 AsyncTask 时传入上下文。

如果这是一个缓慢的过程，那么当您的 Activity 捕获位置更改时，您可以在 AsyncTask 中反向地理编码，然后通过将 doInBackground 反向地理编码的结果传递给 onPostExecute 来显示 Toast（或更新 TextView）在 UI 线程上运行，因此可以安全轻松地更新视图并显示 Toast。

class ReverseGeocodeAsyncTask extends AsyncTask<Void, Void, Void> {

    private Location location;

    public ReverseGeocodeAsyncTask(Location l) { location = l; }

    @Override
    protected String doInBackground(String... params) {
     //do reverse geocoding and return the result
    }

     @Override
     protected void onPostExecute(String result) {
        // update the UI with the result of the reverse geocoding                   
    }
}