安卓 GPS 定位服务

Question

我有一个可以跟踪用户位置的安卓应用程序。它已设置为尽可能使用 Wifi/网络位置服务，否则使用 GPS_PROVIDER 服务。当有 wifi 连接时，它可以正常工作，但是当我设置为仅从 GPS 获取位置时，应用程序崩溃。从测试我有行 location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);实际上并没有设置位置，而是仍然为空。有谁知道为什么会这样？

 package temp;

    import android.app.AlertDialog;
    import android.content.Context;
    import android.content.Intent;
    import android.location.Address;
    import android.location.Geocoder;
    import android.location.Location;
    import android.location.LocationListener;
    import android.location.LocationManager;
    import android.os.Bundle;
    import android.content.DialogInterface;
    import android.provider.Settings;
    import android.util.Log;

    import java.util.List;
    import java.util.Locale;

    public class GPSTracker implements LocationListener {
    private Context context;
    boolean isGPSEnabled = false;
    boolean isNetworkEnabled;
    Location location;
    boolean canGetLocation = false;
    Geocoder geocoder;
    List<Address> addresses;

    double latitude;
    double longitude;

    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 0;
    private static  final long MIN_TIME_BW_UPDATES = 5 * 1000;

    protected LocationManager locationManager;

    public GPSTracker(Context context){
        this.context = context;
        getLocation();
    }

    public Location getLocation(){
        try{
            locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

            isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
            isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if(!isGPSEnabled && !isNetworkEnabled){
                showSettingsAlert();
            }else{
                this.canGetLocation = true;
                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();

                            geocoder = new Geocoder(context, Locale.getDefault());
                            this.addresses = geocoder.getFromLocation(latitude, longitude, 1);
                        }
                    }
                }else{
                    Log.e("GPS_Provider: ", "Made it");
                    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);

                    if(locationManager == null){
                        Log.e("GPS_Provider: ", "Manager1");
                    }else{
                        Log.e("GPS_Provider: ", "Manager2");
                    }

                    if(locationManager != null) {
                        location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);

                        if(location == null){
                            Log.e("GPS_Provider: ", "Made it2");
                        }else{
                            Log.e("GPS_Provider: ", "Made it3");
                        }

                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();

                            Log.e("Cords: ", "latitude: " + latitude + " longitude: " + longitude);

                            geocoder = new Geocoder(context, Locale.getDefault());
                            this.addresses = geocoder.getFromLocation(latitude, longitude, 1);
                        }
                    }
                }
            }

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

    public void stopUsingGps(){
        if(locationManager != null){
            locationManager.removeUpdates(GPSTracker.this);
        }
    }

    public List<Address> getAddress(){
        return this.addresses;
    }

    public double getLatitude(){
        if(location != null){
            latitude = location.getLatitude();
        }
        return  latitude;
    }

    public double getLongitude(){
        if(location != null){
            longitude = location.getLongitude();
        }
        return longitude;
    }

    public boolean canGetLocation(){
        return this.canGetLocation;
    }

    public void showSettingsAlert(){
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(context);

        alertDialog.setTitle("GPS is settings");
        alertDialog.setMessage("GPS is not enabled.");
        alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                context.startActivity(intent);
            }
        });

        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        alertDialog.show();

    }

    @Override
    public void onLocationChanged(Location location) {

    }

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

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }
    }

清单文件

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

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".login"
            android:label="@string/title_activity_login" >
        </activity>
        <activity
            android:name=".Register"
            android:label="@string/title_activity_register" >
        </activity>
    </application>

</manifest>

Answer 1

你得到 null 作为回报，因为如果 GPS 从未真正获得最后一个位置，它就什么也没有给你

您可以查看 FusedLocationProviderAPI，而不是 LocationManager 并自己管理连接问题，它利用了可用的最节能的位置轮询方法，并为您完成所有后台工作。