即使GPS关闭，也会调用onLocationChanged

Question

I have been trying to get the current user location. I turn on the GPS and launch the application. Everything seems to be ok, I can get the current user location.

The problem is when I turn off the GPS and run the application. onLocationChanged() is called. Should it be called with the GPS turned off? If so, why?

package company.com.locationservicesapi;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.provider.Settings;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.GoogleApiClient.ConnectionCallbacks;
import com.google.android.gms.common.api.GoogleApiClient.OnConnectionFailedListener;
import com.google.android.gms.common.api.PendingResult;
import com.google.android.gms.common.api.Status;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;

public class LocationServicesAPIActivity extends Activity implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener {
    private static final String TAG = "Location Service API";
    GoogleApiClient googleApiClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
        if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
            Log.i(TAG, "GPS turned on");
        } else {
            Log.i(TAG, "GPS turned off");
        }

        setContentView(R.layout.activity_location_services_api);
        int result = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        if (result == ConnectionResult.SUCCESS) {
            googleApiClient = new GoogleApiClient.Builder(this)
                    .addApi(LocationServices.API)
                    .addConnectionCallbacks(this)
                    .addOnConnectionFailedListener(this)
                    .build();
            googleApiClient.connect();
        } else {
            GooglePlayServicesUtil.getErrorDialog(result, this, 1).show();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.location_services_api, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onConnected(Bundle bundle) {
        Log.d(TAG, "Connected");
        LocationRequest locationRequest = LocationRequest.create()
                .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
                .setInterval(1000)
                .setNumUpdates(1);

        LocationServices.FusedLocationApi.requestLocationUpdates(googleApiClient, locationRequest, this);
    }

    public void onLocationChanged(Location location) {
        Log.d(TAG, "Location Changed");
        TextView textView = (TextView) findViewById(R.id.textViewLocation);
        textView.setText('@' + location.getLatitude() + "," + location.getLongitude());
    }

    @Override
    public void onConnectionSuspended(int i) {
        Log.d(TAG, "Connection Suspended");
    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        Log.d(TAG, "Connection Failed");
    }
}

activity_location_services_api.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".LocationServicesAPIActivity">

    <TextView
        android:id="@+id/textViewLocation"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</RelativeLayout>

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="company.com.locationservicesapi">

    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme">
        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />

        <activity
            android:name=".LocationServicesAPIActivity"
            android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Logcat output:

10-08 14:18:34.242    4208-4208/company.com.locationservicesapi I/Location Service API﹕ GPS turned off
10-08 14:18:34.625    4208-4208/company.com.locationservicesapi D/Location Service API﹕ Connected
10-08 14:18:35.765    4208-4208/company.com.locationservicesapi D/Location Service API﹕ Location Changed

Answer 1

The FusedLocationApi isn't just calling onLocationChanged() when a valid GPS signal is available. It uses WFPS, Cell-ID and Sensors to get valid locations, too. That's what the FusedLocationApi is all about: Get the most accurate location available using all possibilities of your device.

If you just want to listen to GPS signals, then the only way to do this is using the LocationManager with the flag LocationManager.GPS_PROVIDER as your provider.

Answer 2

you have <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> inside your manifest, so it will use network to access approximate location. see android manifest description

you can remove the location updates everytime you do not have any connections. just declare private LocationManager locationManager; first and put

locationManager.removeUpdates(this);
this.locationManager = null;

on public void onConnectionFailed(ConnectionResult connectionResult)

i hope this helps