如何使用 AsyncTask 获取位置答案

【问题标题】：How To Get Location Using AsyncTask如何使用 AsyncTask 获取位置
【发布时间】：2011-04-15 12:23:13
【问题描述】：

我正在努力寻找解决这个问题的好方法。我制作了我的应用程序，以便它找到我的位置。它似乎过于复杂，但很容易。但是，按照谷歌的建议，我现在尝试将此代码作为异步任务运行，这样它就不会占用 UI。但是我什至无法弄清楚如何让代码编译更不用说实际运行了。错误是当我引用它来删除侦听器时，无法解析 locationManager。我尝试使用此处发布的代码Android find GPS location once, show loading dialog。然而，在这个例子中 currentLocation 似乎没有被任何东西引用，我在试图解决这个问题时遇到了问题。我已经浪费了将近一整天的时间来解决这个问题，所以如果有人能指出我正确的方向，我将不胜感激。

private class LocationControl extends AsyncTask<Context, Void, Location> {
    public Location alocation;
    private LocatoinManager locationManager;

    @Override
    public Location doInBackground(Context... params) {
         locationManager = (LocationManager) params[0].getSystemService(Context.LOCATION_SERVICE);        
          locationManager.requestLocationUpdates(locationManager.GPS_PROVIDER, 0, 0, locationListener);
        return alocation;
    }

    public LocationListener locationListener = new LocationListener() {

            public void onStatusChanged(String provider, int status, Bundle extras) {}
            public void onProviderEnabled(String provider) {}
            public void onProviderDisabled(String provider) {}

            public void onLocationChanged(android.location.Location mlocation) {
                saveLocation(mlocation);
                locationManager.removeUpdates(locationListener);
            }
    };  

    void saveLocation(android.location.Location location){
        alocation = location;   
    }

    @Override
    protected void onPostExecute(Location result) {
        useLocation(result);
        super.onPostExecute(result);
    }

    @Override
    protected void onPreExecute() {
        dialog.show(WasserSportLotse.this, " ", "Finding location...");

        super.onPreExecute();
    }
}

所以我根据您的建议更改了代码，现在可以编译了。我已经更新了这里的代码来代表我正在运行的内容。当 locationManager 请求LocationUpdates 时出现运行时错误。这是logCat。有什么想法吗？

04-15 14:57:56.742: ERROR/AndroidRuntime(18328): Uncaught handler: thread AsyncTask #1 exiting due to uncaught exception
04-15 14:57:56.942: ERROR/AndroidRuntime(18328): java.lang.RuntimeException: An error occured while executing doInBackground()
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:234)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:258)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.FutureTask.run(FutureTask.java:122)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.lang.Thread.run(Thread.java:1060)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.os.Handler.<init>(Handler.java:121)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.location.LocationManager$ListenerTransport$1.<init>(LocationManager.java:128)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.location.LocationManager$ListenerTransport.<init>(LocationManager.java:126)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.location.LocationManager._requestLocationUpdates(LocationManager.java:697)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.location.LocationManager.requestLocationUpdates(LocationManager.java:619)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at com.WasserSportLotse.WasserSportLotse$LocationControl.doInBackground(WasserSportLotse.java:62)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at com.WasserSportLotse.WasserSportLotse$LocationControl.doInBackground(WasserSportLotse.java:1)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256)
04-15 14:57:56.942: ERROR/AndroidRuntime(18328):     ... 4 more
04-15 14:58:23.451: ERROR/AndroidRuntime(18356): Uncaught handler: thread AsyncTask #1 exiting due to uncaught exception
04-15 14:58:23.642: ERROR/AndroidRuntime(18356): java.lang.RuntimeException: An error occured while executing doInBackground()
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:234)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:258)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.FutureTask.run(FutureTask.java:122)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.lang.Thread.run(Thread.java:1060)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.os.Handler.<init>(Handler.java:121)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.location.LocationManager$ListenerTransport$1.<init>(LocationManager.java:128)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.location.LocationManager$ListenerTransport.<init>(LocationManager.java:126)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.location.LocationManager._requestLocationUpdates(LocationManager.java:697)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.location.LocationManager.requestLocationUpdates(LocationManager.java:619)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at com.WasserSportLotse.WasserSportLotse$LocationControl.doInBackground(WasserSportLotse.java:62)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at com.WasserSportLotse.WasserSportLotse$LocationControl.doInBackground(WasserSportLotse.java:1)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256)
04-15 14:58:23.642: ERROR/AndroidRuntime(18356):     ... 4 more

【问题讨论】：

标签： android location android-asynctask

【解决方案1】：

public class FastMainActivity extends Activity {

    Button searchBtn = null;
    Intent locatorService = null;
    AlertDialog alertDialog = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        searchBtn = (Button) findViewById(R.id.searchBtn);

        searchBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                if (!startService()) {
                    CreateAlert("Error!", "Service Cannot be started");
                } else {
                    Toast.makeText(FastMainActivity.this, "Service Started",
                            Toast.LENGTH_LONG).show();
                }

            }
        });

    }

    public boolean stopService() {
        if (this.locatorService != null) {
            this.locatorService = null;
        }
        return true;
    }

    public boolean startService() {
        try {
            // this.locatorService= new
            // Intent(FastMainActivity.this,LocatorService.class);
            // startService(this.locatorService);

            FetchCordinates fetchCordinates = new FetchCordinates();
            fetchCordinates.execute();
            return true;
        } catch (Exception error) {
            return false;
        }

    }

    public AlertDialog CreateAlert(String title, String message) {
        AlertDialog alert = new AlertDialog.Builder(this).create();

        alert.setTitle(title);

        alert.setMessage(message);

        return alert;

    }

    public class FetchCordinates extends AsyncTask<String, Integer, String> {
        ProgressDialog progDailog = null;

        public double lati = 0.0;
        public double longi = 0.0;

        public LocationManager mLocationManager;
        public VeggsterLocationListener mVeggsterLocationListener;

        @Override
        protected void onPreExecute() {
            mVeggsterLocationListener = new VeggsterLocationListener();
            mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

            mLocationManager.requestLocationUpdates(
                    LocationManager.NETWORK_PROVIDER, 0, 0,
                    mVeggsterLocationListener);

            progDailog = new ProgressDialog(FastMainActivity.this);
            progDailog.setOnCancelListener(new OnCancelListener() {
                @Override
                public void onCancel(DialogInterface dialog) {
                    FetchCordinates.this.cancel(true);
                }
            });
            progDailog.setMessage("Loading...");
            progDailog.setIndeterminate(true);
            progDailog.setCancelable(true);
            progDailog.show();

        }

        @Override
        protected void onCancelled(){
            System.out.println("Cancelled by user!");
            progDialog.dismiss();
            mLocationManager.removeUpdates(mVeggsterLocationListener);
        }

        @Override
        protected void onPostExecute(String result) {
            progDailog.dismiss();

            Toast.makeText(FastMainActivity.this,
                    "LATITUDE :" + lati + " LONGITUDE :" + longi,
                    Toast.LENGTH_LONG).show();
        }

        @Override
        protected String doInBackground(String... params) {
            // TODO Auto-generated method stub

            while (this.lati == 0.0) {

            }
            return null;
        }

        public class VeggsterLocationListener implements LocationListener {

            @Override
            public void onLocationChanged(Location location) {

                int lat = (int) location.getLatitude(); // * 1E6);
                int log = (int) location.getLongitude(); // * 1E6);
                int acc = (int) (location.getAccuracy());

                String info = location.getProvider();
                try {

                    // LocatorService.myLatitude=location.getLatitude();

                    // LocatorService.myLongitude=location.getLongitude();

                    lati = location.getLatitude();
                    longi = location.getLongitude();

                } catch (Exception e) {
                    // progDailog.dismiss();
                    // Toast.makeText(getApplicationContext(),"Unable to get Location"
                    // , Toast.LENGTH_LONG).show();
                }

            }

            @Override
            public void onProviderDisabled(String provider) {
                Log.i("OnProviderDisabled", "OnProviderDisabled");
            }

            @Override
            public void onProviderEnabled(String provider) {
                Log.i("onProviderEnabled", "onProviderEnabled");
            }

            @Override
            public void onStatusChanged(String provider, int status,
                    Bundle extras) {
                Log.i("onStatusChanged", "onStatusChanged");

            }

        }

    }

}

【讨论】：

@All 这是完美的代码 sn-p，用于在使用 Aysnc 任务和进度对话框时获取位置（GPS 坐标）。
+1。这是一个很好的例子，可以避免 Loopers，这可能会造成混淆。
这段代码不在后台运行位置管理器，而是在 UI 线程中运行的 onPreExecute() 方法中。
@SpinalTapFan11 同意，它用一个简单的循环替换它，while (this.lati == 0.0) {}。
@SALMAN 你能解释一下当 doInBackground() 方法只是循环（等待）什么都不做时异步任务的用途......并且所有工作负载都在 Ui 线程上

【解决方案2】：

在调用locationManager.requestLocationUpdates(locationManager.GPS_PROVIDER, 0, 0, locationListener);之前添加Looper.prepare() 之后记得调用 Looper.loop()。

【讨论】：

如果我想停止这个循环怎么办？

【解决方案3】：

首先解决您的编译问题，移动

LocationManager locationManager = (LocationManager)params[0].getSystemService(Context.LOCATION_SERVICE);

所以它是类的私有成员变量。

LocationManager 不必在 AsyncTask 中。它不会占用 UI，所有更新都已经是异步的。这只会给您的项目增加不必要的复杂性。

您可能只需将 useLocation 移至 onLockationChanged。

【讨论】：

我建议摆脱 AsyncTask。运行时错误可能会消失。
这就是我最初让应用程序工作的方式，但是我有一个启动屏幕，我想在获得位置时显示一个对话框。执行此操作时对话框冻结。因此需要异步任务。
@Mike 你有解释LocationManager 如何异步工作的参考吗？我在参考页面上找不到任何关于它的内容。

【解决方案4】：

public Location getLocation() 
{

    try 
    {
        locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE);

        // getting GPS status
        isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);

        // getting network status
        isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if (!isGPSEnabled && !isNetworkEnabled) 
        {
            // no network provider is enabled
            Log.w("DOCOMO-2","Network Connection failed");
        } 
        else 
        {
            this.canGetLocation = true;
            // First get location from Network Provider
            if (isNetworkEnabled) 
            {

                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                if (locationManager != null) 
                {
                    location = locationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) 
                    {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) 
            {
                if (location == null) 
                {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    if (locationManager != null) 
                    {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) 
                        {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }

                    }
                }
            }
        }
        locationManager=null;
        location=null;

    } 
    catch (Exception e) 
    {
        locationManager=null;
        location=null;
        e.printStackTrace();
    }
    return location;
}

【讨论】：