我已经对这个主题进行了很多天的认真研究......我在这里也看到了很多主题...... 但不幸的是我找不到解决方案....

我正在编写一个使用新的 Google API for Geofence 的应用程序... 好吧，我可以处理地理围栏的“输入”和“输出”，但前提是我的应用程序已打开!即使我打开了 wifi、gps 和 3G，但应用程序不会触发任何事件...只要应用程序打开...

我正在使用与文档 http://developer.android.com/training/location/geofencing.html 完全相同的 GeofenceRequester 类.

即使类(class)相同，我也会在此处发布代码:

package br.com.marrs.imhere.geofence;
import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentSender.SendIntentException;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.util.Log;
import br.com.marrs.imhere.services.ReceiveTransitionsIntentService;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesClient;
import com.google.android.gms.common.GooglePlayServicesClient.ConnectionCallbacks;
import com.google.android.gms.common.GooglePlayServicesClient.OnConnectionFailedListener;
import com.google.android.gms.location.Geofence;
import com.google.android.gms.location.LocationClient;
import com.google.android.gms.location.LocationClient.OnAddGeofencesResultListener;
import com.google.android.gms.location.LocationStatusCodes;

/**
 * Class for connecting to Location Services and requesting geofences.
 * <b>
 * Note: Clients must ensure that Google Play services is available before requesting geofences.
 * </b> Use GooglePlayServicesUtil.isGooglePlayServicesAvailable() to check.
 *
 *
 * To use a GeofenceRequester, instantiate it and call AddGeofence(). Everything else is done
 * automatically.
 *
 */
public class GeofenceRequester
                implements
                    OnAddGeofencesResultListener,
                    ConnectionCallbacks,
                    OnConnectionFailedListener {

    // Storage for a reference to the calling client
    private final Activity mActivity;

    // Stores the PendingIntent used to send geofence transitions back to the app
    private PendingIntent mGeofencePendingIntent;

    // Stores the current list of geofences
    private ArrayList<Geofence> mCurrentGeofences;

    // Stores the current instantiation of the location client
    private LocationClient mLocationClient;

    /*
     * Flag that indicates whether an add or remove request is underway. Check this
     * flag before attempting to start a new request.
     */
    private boolean mInProgress;

    public GeofenceRequester(Activity activityContext) {
        // Save the context
        mActivity = activityContext;

        // Initialize the globals to null
        mGeofencePendingIntent = null;
        mLocationClient = null;
        mInProgress = false;
    }

    /**
     * Set the "in progress" flag from a caller. This allows callers to re-set a
     * request that failed but was later fixed.
     *
     * @param flag Turn the in progress flag on or off.
     */
    public void setInProgressFlag(boolean flag) {
        // Set the "In Progress" flag.
        mInProgress = flag;
    }

    /**
     * Get the current in progress status.
     *
     * @return The current value of the in progress flag.
     */
    public boolean getInProgressFlag() {
        return mInProgress;
    }

    /**
     * Returns the current PendingIntent to the caller.
     *
     * @return The PendingIntent used to create the current set of geofences
     */
    public PendingIntent getRequestPendingIntent() {
        return createRequestPendingIntent();
    }

    /**
     * Start adding geofences. Save the geofences, then start adding them by requesting a
     * connection
     *
     * @param geofences A List of one or more geofences to add
     */
    public void addGeofences(List<Geofence> geofences) throws UnsupportedOperationException {

        /*
         * Save the geofences so that they can be sent to Location Services once the
         * connection is available.
         */
        mCurrentGeofences = (ArrayList<Geofence>) geofences;

        // If a request is not already in progress
        if (!mInProgress) {

            // Toggle the flag and continue
            mInProgress = true;

            // Request a connection to Location Services
            requestConnection();

        // If a request is in progress
        } else {

            // Throw an exception and stop the request
            throw new UnsupportedOperationException();
        }
    }

    /**
     * Request a connection to Location Services. This call returns immediately,
     * but the request is not complete until onConnected() or onConnectionFailure() is called.
     */
    private void requestConnection() 
    {
        getLocationClient().connect();
    }

    /**
     * Get the current location client, or create a new one if necessary.
     *
     * @return A LocationClient object
     */
    private GooglePlayServicesClient getLocationClient()
    {
        if (mLocationClient == null) {

            mLocationClient = new LocationClient(mActivity, this, this);
        }
        return mLocationClient;

    }
    /**
     * Once the connection is available, send a request to add the Geofences
     */
    private void continueAddGeofences() {

        // Get a PendingIntent that Location Services issues when a geofence transition occurs
        mGeofencePendingIntent = createRequestPendingIntent();

        // Send a request to add the current geofences
        mLocationClient.addGeofences(mCurrentGeofences, mGeofencePendingIntent, this);
    }

    /*
     * Handle the result of adding the geofences
     */
    @Override
    public void onAddGeofencesResult(int statusCode, String[] geofenceRequestIds) 
    {
        // Create a broadcast Intent that notifies other components of success or failure
        Intent broadcastIntent = new Intent();

        // Temp storage for messages
        String msg;

        // If adding the geocodes was successful
        if (LocationStatusCodes.SUCCESS == statusCode) 
        {
            // Create a message containing all the geofence IDs added.
            msg = geofenceRequestIds.toString();

            // In debug mode, log the result
            Log.d("DEBUG", msg);

            // Create an Intent to broadcast to the app
            broadcastIntent.setAction("br.com.marrs.imhere.ACTION_GEOFENCES_ADDED")
                           .addCategory("br.com.marrs.imhere.CATEGORY_LOCATION_SERVICES")
                           .putExtra("br.com.marrs.imhere.EXTRA_GEOFENCE_STATUS", msg);
        // If adding the geofences failed
        } 
        else
        {

            /*
             * Create a message containing the error code and the list
             * of geofence IDs you tried to add
             */
            msg = "Erro adicionando geofence";

            // Log an error
            Log.e("DEBUG", msg);

            // Create an Intent to broadcast to the app
            broadcastIntent.setAction("br.com.marrs.imhere.ACTION_GEOFENCE_ERROR")
                           .addCategory("br.com.marrs.imhere.CATEGORY_LOCATION_SERVICES")
                           .putExtra("br.com.marrs.imhere.EXTRA_GEOFENCE_STATUS", msg);
        }

        // Broadcast whichever result occurred
        LocalBroadcastManager.getInstance(mActivity).sendBroadcast(broadcastIntent);

        // Disconnect the location client
        requestDisconnection();
    }

    /**
     * Get a location client and disconnect from Location Services
     */
    private void requestDisconnection() {

        // A request is no longer in progress
        mInProgress = false;

        getLocationClient().disconnect();
    }

    /*
     * Called by Location Services once the location client is connected.
     *
     * Continue by adding the requested geofences.
     */
    @Override
    public void onConnected(Bundle arg0) {
        // If debugging, log the connection

        Log.d("DEBUG", "GeofenceRequester connected");

        // Continue adding the geofences
        continueAddGeofences();
    }

    /*
     * Called by Location Services once the location client is disconnected.
     */
    @Override
    public void onDisconnected() {


        // Turn off the request flag
        mInProgress = false;

        // In debug mode, log the disconnection
        Log.d("DEBUG", "GeofenceRequester disconnected");

        // Destroy the current location client
        mLocationClient = null;
    }

    /**
     * Get a PendingIntent to send with the request to add Geofences. Location Services issues
     * the Intent inside this PendingIntent whenever a geofence transition occurs for the current
     * list of geofences.
     *
     * @return A PendingIntent for the IntentService that handles geofence transitions.
     */
    private PendingIntent createRequestPendingIntent() {

        // If the PendingIntent already exists
        if (null != mGeofencePendingIntent) {

            // Return the existing intent
            return mGeofencePendingIntent;

        // If no PendingIntent exists
        } else {

            // Create an Intent pointing to the IntentService
            Intent intent = new Intent(mActivity, ReceiveTransitionsIntentService.class);
            /*
             * Return a PendingIntent to start the IntentService.
             * Always create a PendingIntent sent to Location Services
             * with FLAG_UPDATE_CURRENT, so that sending the PendingIntent
             * again updates the original. Otherwise, Location Services
             * can't match the PendingIntent to requests made with it.
             */
            return PendingIntent.getService(
                    mActivity,
                    0,
                    intent,
                    PendingIntent.FLAG_UPDATE_CURRENT);
        }
    }

    /*
     * Implementation of OnConnectionFailedListener.onConnectionFailed
     * If a connection or disconnection request fails, report the error
     * connectionResult is passed in from Location Services
     */
    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

        // Turn off the request flag
        mInProgress = false;

        /*
         * Google Play services can resolve some errors it detects.
         * If the error has a resolution, try sending an Intent to
         * start a Google Play services activity that can resolve
         * error.
         */
        if (connectionResult.hasResolution()) {

            try {
                // Start an Activity that tries to resolve the error
                connectionResult.startResolutionForResult(mActivity, 9000);

            /*
             * Thrown if Google Play services canceled the original
             * PendingIntent
             */
            } catch (SendIntentException e) {
                // Log the error
                e.printStackTrace();
            }

        /*
         * If no resolution is available, put the error code in
         * an error Intent and broadcast it back to the main Activity.
         * The Activity then displays an error dialog.
         * is out of date.
         */
        } else {

            Intent errorBroadcastIntent = new Intent("br.com.marrs.imhere.ACTION_CONNECTION_ERROR");
            errorBroadcastIntent.addCategory("br.com.marrs.imhere.CATEGORY_LOCATION_SERVICES")
                                .putExtra("br.com.marrs.imhere.EXTRA_CONNECTION_ERROR_CODE",
                                        connectionResult.getErrorCode());
            LocalBroadcastManager.getInstance(mActivity).sendBroadcast(errorBroadcastIntent);
        }
    }
}

和服务:

package br.com.marrs.imhere.services;
import br.com.marrs.imhere.ImHereActivity;
import br.com.marrs.imhere.R;

import com.google.android.gms.location.Geofence;
import com.google.android.gms.location.LocationClient;

import android.app.IntentService;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.support.v4.app.NotificationCompat;
import android.support.v4.app.TaskStackBuilder;
import android.support.v4.content.LocalBroadcastManager;
import android.text.TextUtils;
import android.util.Log;

import java.util.List;

/**
 * This class receives geofence transition events from Location Services, in the
 * form of an Intent containing the transition type and geofence id(s) that triggered
 * the event.
 */
public class ReceiveTransitionsIntentService extends IntentService {

    /**
     * Sets an identifier for this class' background thread
     */
    public ReceiveTransitionsIntentService() 
    {
        super("ReceiveTransitionsIntentService");
    }

    /**
     * Handles incoming intents
     * @param intent The Intent sent by Location Services. This Intent is provided
     * to Location Services (inside a PendingIntent) when you call addGeofences()
     */
    @Override
    protected void onHandleIntent(Intent intent) {

        // Create a local broadcast Intent
        Intent broadcastIntent = new Intent();

        // Give it the category for all intents sent by the Intent Service
        broadcastIntent.addCategory("br.com.marrs.imhere.CATEGORY_LOCATION_SERVICES");

        // First check for errors
        if (LocationClient.hasError(intent)) {

            // Get the error code
            int errorCode = LocationClient.getErrorCode(intent);


            // Log the error
            Log.e("DEBUG", "Erro no service LocationClient has error");

            // Set the action and error message for the broadcast intent
            broadcastIntent.setAction("br.com.marrs.imhere.ACTION_GEOFENCES_ERROR").putExtra("br.com.marrs.imhere.EXTRA_GEOFENCE_STATUS", "problemas");

            // Broadcast the error *locally* to other components in this app
            LocalBroadcastManager.getInstance(this).sendBroadcast(broadcastIntent);

        // If there's no error, get the transition type and create a notification
        } else {

            // Get the type of transition (entry or exit)
            int transition = LocationClient.getGeofenceTransition(intent);

            // Test that a valid transition was reported
            if (
                    (transition == Geofence.GEOFENCE_TRANSITION_ENTER)
                    ||
                    (transition == Geofence.GEOFENCE_TRANSITION_EXIT)
               ) {

                // Post a notification
                List<Geofence> geofences = LocationClient.getTriggeringGeofences(intent);
                String[] geofenceIds = new String[geofences.size()];
                for (int index = 0; index < geofences.size() ; index++) {
                    geofenceIds[index] = geofences.get(index).getRequestId();
                }
                String ids = TextUtils.join(",",geofenceIds);
                String transitionType = getTransitionString(transition);

                sendNotification(transitionType, ids);

                // Log the transition type and a message
                Log.d("DEBUG","Ae...n sei pq isso....mas parece que tah ok");

            // An invalid transition was reported
            } else {
                // Always log as an error
                Log.e("DEBUG","Erro, erro, erro");
            }
        }
    }

    /**
     * Posts a notification in the notification bar when a transition is detected.
     * If the user clicks the notification, control goes to the main Activity.
     * @param transitionType The type of transition that occurred.
     *
     */
    private void sendNotification(String transitionType, String ids)
    {

        // Create an explicit content Intent that starts the main Activity
        Intent notificationIntent =
                new Intent(getApplicationContext(),ImHereActivity.class);

        // Construct a task stack
        TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);

        // Adds the main Activity to the task stack as the parent
        stackBuilder.addParentStack(ImHereActivity.class);

        // Push the content Intent onto the stack
        stackBuilder.addNextIntent(notificationIntent);

        // Get a PendingIntent containing the entire back stack
        PendingIntent notificationPendingIntent =
                stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);

        // Get a notification builder that's compatible with platform versions >= 4
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);

        // Set the notification contents
        builder.setSmallIcon(R.drawable.abs__ic_clear)
               .setContentTitle(ids)
               .setContentText(transitionType)
               .setContentIntent(notificationPendingIntent);

        // Get an instance of the Notification manager
        NotificationManager mNotificationManager =
            (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        // Issue the notification
        mNotificationManager.notify(0, builder.build());
    }

    /**
     * Maps geofence transition types to their human-readable equivalents.
     * @param transitionType A transition type constant defined in Geofence
     * @return A String indicating the type of transition
     */
    private String getTransitionString(int transitionType) {
        switch (transitionType) {

            case Geofence.GEOFENCE_TRANSITION_ENTER:
                return "Entrando";

            case Geofence.GEOFENCE_TRANSITION_EXIT:
                return "Saindo";

            default:
                return "Desconhecido";
        }
    }
}

Activity 中的广播接收器:

public class GeofenceSampleReceiver extends BroadcastReceiver 
    {
        /*
         * Define the required method for broadcast receivers
         * This method is invoked when a broadcast Intent triggers the receiver
         */
        @Override
        public void onReceive(Context context, Intent intent) 
        {

            // Check the action code and determine what to do
            String action = intent.getAction();

            // Intent contains information about errors in adding or removing geofences
            if (TextUtils.equals(action, "br.com.marrs.imhere.ACTION_GEOFENCE_ERROR"))
            {

                handleGeofenceError(context, intent);

            // Intent contains information about successful addition or removal of geofences
            } 
            else if (
                    TextUtils.equals(action, "br.com.marrs.imhere.ACTION_GEOFENCES_ADDED")
                    ||
                    TextUtils.equals(action, "br.com.marrs.imhere.ACTION_GEOFENCES_REMOVED")) 
            {

                handleGeofenceStatus(context, intent);

            // Intent contains information about a geofence transition
            } else if (TextUtils.equals(action, "br.com.marrs.imhere.ACTION_GEOFENCE_TRANSITION")) 
            {

                handleGeofenceTransition(context, intent);

            // The Intent contained an invalid action
            } 
            else 
            {
                Log.e("DEBUG", "Invalid action detail");
                Toast.makeText(context, "Invalid action detail", Toast.LENGTH_LONG).show();
            }
        }

        /**
         * If you want to display a UI message about adding or removing geofences, put it here.
         *
         * @param context A Context for this component
         * @param intent The received broadcast Intent
         */
        private void handleGeofenceStatus(Context context, Intent intent) {

        }

        /**
         * Report geofence transitions to the UI
         *
         * @param context A Context for this component
         * @param intent The Intent containing the transition
         */
        private void handleGeofenceTransition(Context context, Intent intent) {
            /*
             * If you want to change the UI when a transition occurs, put the code
             * here. The current design of the app uses a notification to inform the
             * user that a transition has occurred.
             */
        }

        /**
         * Report addition or removal errors to the UI, using a Toast
         *
         * @param intent A broadcast Intent sent by ReceiveTransitionsIntentService
         */
        private void handleGeofenceError(Context context, Intent intent) 
        {
            String msg = intent.getStringExtra("br.com.marrs.imhere.EXTRA_GEOFENCE_STATUS");
            Log.e("DEBUG", msg);
            Toast.makeText(context, msg, Toast.LENGTH_LONG).show();
        }
    }

这是我在发送到 GeofenceRequester 之前用来创建 GEofence 的一段代码。

int raio = Integer.parseInt(spinner.getAdapter().getItem(spinner.getSelectedItemPosition()).toString());
            int transitionType = (in.isChecked())?Geofence.GEOFENCE_TRANSITION_ENTER:Geofence.GEOFENCE_TRANSITION_EXIT;
            Geofence geofence = new Geofence.Builder().setRequestId(nomeGeofence.getText().toString()).setTransitionTypes(transitionType).setCircularRegion(lat, lon, raio).setExpirationDuration(Geofence.NEVER_EXPIRE).build();
            geofences.add(geofence);

            try 
            {
                mGeofenceRequester.addGeofences(geofences);
                addCircleGeofence(raio);
            }
            catch (UnsupportedOperationException e) 
            {
                Toast.makeText(getActivity(), "Já existe uma requisição de add em andamento",Toast.LENGTH_LONG).show();
            }

任何帮助都会很棒! 谢谢!

最佳答案

我有完全相同的 problem .这是我在那里回答的内容:所以在尝试了一下之后，看起来 ReceiveTransitionsIntentService(如示例代码中所定义)将在应用程序不存在时停止接收通知。我认为这是示例代码的一个大问题……似乎这会让像我这样的人感到困惑。

所以我改用广播接收器，到目前为止，从我的测试来看它似乎工作正常。

将此添加到 list 中:

<receiver android:name="com.aol.android.geofence.GeofenceReceiver"
        android:exported="false">
        <intent-filter >
            <action android:name="com.aol.android.geofence.ACTION_RECEIVE_GEOFENCE"/>
        </intent-filter>
    </receiver>

然后在 GeofenceRequester 类中，您需要更改 createRequestPendingIntent 方法，以便它转到您的 BroadcastReceiver 而不是 ReceiveTransitionsIntentService。确定并注意对 .getBroadcast 而不是 getService 的更改。这让我挂了一会儿电话。

private PendingIntent createRequestPendingIntent() {

        // If the PendingIntent already exists
        if (null != mGeofencePendingIntent) {

            // Return the existing intent
            return mGeofencePendingIntent;

        // If no PendingIntent exists
        } else {

            // Create an Intent pointing to the IntentService
            Intent intent = new Intent("com.aol.android.geofence.ACTION_RECEIVE_GEOFENCE");

            //MAKE SURE YOU CHANGE THIS TO getBroadcast if you are coming from the sample code.
            return PendingIntent.getBroadcast(
                    context,
                    0,
                    intent,
                    PendingIntent.FLAG_UPDATE_CURRENT);
        }
    }

然后我添加了如下所示的 GeofenceReceiver 类:

public class GeofenceReceiver extends BroadcastReceiver {
    Context context;

    Intent broadcastIntent = new Intent();

    @Override
    public void onReceive(Context context, Intent intent) {
        this.context = context;

        broadcastIntent.addCategory(GeofenceUtils.CATEGORY_LOCATION_SERVICES);

        if (LocationClient.hasError(intent)) {
            handleError(intent);
        } else {
            handleEnterExit(intent);
        }
    }

    private void handleError(Intent intent){
        // Get the error code
        int errorCode = LocationClient.getErrorCode(intent);

        // Get the error message
        String errorMessage = LocationServiceErrorMessages.getErrorString(
                context, errorCode);

        // Log the error
        Log.e(GeofenceUtils.APPTAG,
                context.getString(R.string.geofence_transition_error_detail,
                        errorMessage));

        // Set the action and error message for the broadcast intent
        broadcastIntent
                .setAction(GeofenceUtils.ACTION_GEOFENCE_ERROR)
                .putExtra(GeofenceUtils.EXTRA_GEOFENCE_STATUS, errorMessage);

        // Broadcast the error *locally* to other components in this app
        LocalBroadcastManager.getInstance(context).sendBroadcast(
                broadcastIntent);
    }


    private void handleEnterExit(Intent intent) {
        // Get the type of transition (entry or exit)
        int transition = LocationClient.getGeofenceTransition(intent);

        // Test that a valid transition was reported
        if ((transition == Geofence.GEOFENCE_TRANSITION_ENTER)
                || (transition == Geofence.GEOFENCE_TRANSITION_EXIT)) {

            // Post a notification
            List<Geofence> geofences = LocationClient
                    .getTriggeringGeofences(intent);
            String[] geofenceIds = new String[geofences.size()];
            String ids = TextUtils.join(GeofenceUtils.GEOFENCE_ID_DELIMITER,
                    geofenceIds);
            String transitionType = GeofenceUtils
                    .getTransitionString(transition);

            for (int index = 0; index < geofences.size(); index++) {
                Geofence geofence = geofences.get(index);
                ...do something with the geofence entry or exit. I'm saving them to a local sqlite db

            }
            // Create an Intent to broadcast to the app
            broadcastIntent
                    .setAction(GeofenceUtils.ACTION_GEOFENCE_TRANSITION)
                    .addCategory(GeofenceUtils.CATEGORY_LOCATION_SERVICES)
                    .putExtra(GeofenceUtils.EXTRA_GEOFENCE_ID, geofenceIds)
                    .putExtra(GeofenceUtils.EXTRA_GEOFENCE_TRANSITION_TYPE,
                            transitionType);

            LocalBroadcastManager.getInstance(MyApplication.getContext())
                    .sendBroadcast(broadcastIntent);

            // Log the transition type and a message
            Log.d(GeofenceUtils.APPTAG, transitionType + ": " + ids);
            Log.d(GeofenceUtils.APPTAG,
                    context.getString(R.string.geofence_transition_notification_text));

            // In debug mode, log the result
            Log.d(GeofenceUtils.APPTAG, "transition");

            // An invalid transition was reported
        } else {
            // Always log as an error
            Log.e(GeofenceUtils.APPTAG,
                    context.getString(R.string.geofence_transition_invalid_type,
                            transition));
        }
    }

    /**
     * Posts a notification in the notification bar when a transition is
     * detected. If the user clicks the notification, control goes to the main
     * Activity.
     * 
     * @param transitionType
     *            The type of transition that occurred.
     * 
     */
    private void sendNotification(String transitionType, String locationName) {

        // Create an explicit content Intent that starts the main Activity
        Intent notificationIntent = new Intent(context, MainActivity.class);

        // Construct a task stack
        TaskStackBuilder stackBuilder = TaskStackBuilder.create(context);

        // Adds the main Activity to the task stack as the parent
        stackBuilder.addParentStack(MainActivity.class);

        // Push the content Intent onto the stack
        stackBuilder.addNextIntent(notificationIntent);

        // Get a PendingIntent containing the entire back stack
        PendingIntent notificationPendingIntent = stackBuilder
                .getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);

        // Get a notification builder that's compatible with platform versions
        // >= 4
        NotificationCompat.Builder builder = new NotificationCompat.Builder(
                context);

        // Set the notification contents
        builder.setSmallIcon(R.drawable.ic_notification)
                .setContentTitle(transitionType + ": " + locationName)
                .setContentText(
                        context.getString(R.string.geofence_transition_notification_text))
                .setContentIntent(notificationPendingIntent);

        // Get an instance of the Notification manager
        NotificationManager mNotificationManager = (NotificationManager) context
                .getSystemService(Context.NOTIFICATION_SERVICE);

        // Issue the notification
        mNotificationManager.notify(0, builder.build());
    }
}

希望这对其他人有帮助。

关于Android Geofence 仅适用于打开的应用程序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19434999/