在空对象引用上调用虚拟方法“double android.location.Location.getLatitude()”时出错

Question

我要做的就是让用户获得他喜欢的类型的位置列表。例如，如果输入是医院，我的应用程序将使用搜索字符串“医院”打开谷歌地图。但正如文档中所建议的那样，使用geo:0,0?q=hospital uri 之类的地理编码显示坐标 0 纬度和 0 经度附近的所有医院。因此，当我尝试使用以下代码首先获取用户坐标时。

地点解码器.java

package com.kkze.Mappy;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationManager;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.provider.Settings;
import android.text.TextUtils;
import android.util.Log;
import android.widget.Toast;

public class PlacesDecoder extends Activity {
Intent intentThatCalled;
public double latitude;
public double longitude;
public LocationManager locationManager;
public Criteria criteria;
public String bestProvider;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    intentThatCalled = getIntent();
    String voice2text = intentThatCalled.getStringExtra("v2txt");
    getLocation(voice2text);
}
public static boolean isLocationEnabled(Context context)
{
    int locationMode = 0;
    String locationProviders;
    if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)
    {
        try
        {
            locationMode = Settings.Secure.getInt(context.getContentResolver(), Settings.Secure.LOCATION_MODE);
        } catch (Settings.SettingNotFoundException e) {
            e.printStackTrace();
        }
        return locationMode != Settings.Secure.LOCATION_MODE_OFF;
    }
    else
    {
        locationProviders = Settings.Secure.getString(context.getContentResolver(), Settings.Secure.LOCATION_PROVIDERS_ALLOWED);
        return !TextUtils.isEmpty(locationProviders);
    }
}

public void getLocation(String voice2txt) {
    locationManager = (LocationManager)  this.getSystemService(Context.LOCATION_SERVICE);
    criteria = new Criteria();
    bestProvider = String.valueOf(locationManager.getBestProvider(criteria, true)).toString();
    Location location = locationManager.getLastKnownLocation(bestProvider);
    if (isLocationEnabled(PlacesDecoder.this)) {
            Log.e("TAG", "GPS is on");
            latitude = location.getLatitude();
            longitude = location.getLongitude();
            Toast.makeText(PlacesDecoder.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
            searchNearestPlace(voice2txt);

        }
    else
    {
        AlertDialog.Builder notifyLocationServices = new AlertDialog.Builder(PlacesDecoder.this);
        notifyLocationServices.setTitle("Switch on Location Services");
        notifyLocationServices.setMessage("Location Services must be turned on to complete this action. Also please take note that if on a very weak network connection,  such as 'E' Mobile Data or 'Very weak Wifi-Connections' it may take even 15 mins to load. If on a very weak network connection as stated above, location returned to application may be null or nothing and cause the application to crash.");
        notifyLocationServices.setPositiveButton("Ok, Open Settings", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Intent openLocationSettings = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                PlacesDecoder.this.startActivity(openLocationSettings);
                finish();
            }
        });
        notifyLocationServices.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }
        });
        notifyLocationServices.show();
    }
}

public void searchNearestPlace(String v2txt) {
    Log.e("TAG", "Started");
    v2txt = v2txt.toLowerCase();
    String[] placesS = {"accounting", "airport", "aquarium", "atm", "attraction", "bakery", "bakeries", "bank", "bar", "cafe", "campground", "casino", "cemetery", "cemeteries", "church", "courthouse", "dentist", "doctor", "electrician", "embassy", "embassies", "establishment", "finance", "florist", "food", "grocery", "groceries", "supermarket", "gym", "health", "hospital", "laundry", "laundries", "lawyer", "library", "libraries", "locksmith", "lodging", "mosque", "museum", "painter", "park", "parking", "pharmacy", "pharmacies", "physiotherapist", "plumber", "police", "restaurant", "school", "spa", "stadium", "storage", "store", "synagog", "synagogue", "university", "universities", "zoo"};
    String[] placesM = {"amusement park", "animal care", "animal care", "animal hospital", "art gallery", "art galleries", "beauty salon", "bicycle store", "book store", "bowling alley", "bus station", "car dealer", "car rental", "car repair", "car wash", "city hall", "clothing store", "convenience store", "department store", "electronics store", "electronic store", "fire station", "funeral home", "furniture store", "gas station", "general contractor", "hair care", "hardware store", "hindu temple", "home good store", "homes good store", "home goods store", "homes goods store", "insurance agency", "insurance agencies", "jewelry store", "liquor store", "local government office", "meal delivery", "meal deliveries", "meal takeaway", "movie rental", "movie theater", "moving company", "moving companies", "night club", "pet store", "place of worship", "places of worship", "post office", "real estate agency", "real estate agencies", "roofing contractor", "rv park", "shoe store", "shopping mall", "subway station", "taxi stand", "train station", "travel agency", "travel agencies", "veterinary care"};
    int index;
    for (int i = 0; i <= placesM.length - 1; i++) {
        Log.e("TAG", "forM");
        if (v2txt.contains(placesM[i])) {
            Log.e("TAG", "sensedM?!");
            index = i;
            Uri gmmIntentUri = Uri.parse("geo:" + latitude + "," + longitude + "?q=" + placesM[index]);
            Intent mapIntent = new Intent(Intent.ACTION_VIEW, gmmIntentUri);
            mapIntent.setPackage("com.google.android.apps.maps");
            startActivity(mapIntent);
            finish();
        }
    }
    for (int i = 0; i <= placesS.length - 1; i++) {
        Log.e("TAG", "forS");
        if (v2txt.contains(placesS[i])) {
            Log.e("TAG", "sensedS?!");
            index = i;
            Uri gmmIntentUri = Uri.parse("geo:" + latitude + "," + longitude + "?q=" + placesS[index]);
            Intent mapIntent = new Intent(Intent.ACTION_VIEW, gmmIntentUri);
            mapIntent.setPackage("com.google.android.apps.maps");
            startActivity(mapIntent);
            finish();
        }
    }
}
}

问题是总是和总是位置返回空值。而且我知道一个事实，只要启用了位置，另一个应用程序 Jarvis 就可以轻松完成任务，如果没有，则只是要求用户这样做。但在相同条件下，我的应用程序总是崩溃。

我做了什么：

1. 日日夜夜试图解决这个问题。
2. 浏览了许多关于该主题的页面。
3. 尝试了我自己的不同代码。

它仍然会发生。我是Android的初学者。 请帮帮我。有没有办法解决我的问题？甚至认为其他应用程序以某种方式设法做到了。

这是我的 LogCat。

Process: com.kkze.Mappy, PID: 6742
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kkze.Mappy/com.kkze.Mappy.PlacesDecoder}: java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
        at android.app.ActivityThread.access$900(ActivityThread.java:172)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:145)
        at android.app.ActivityThread.main(ActivityThread.java:5832)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference
        at com.kkze.Mappy.PlacesDecoder.getLocation(PlacesDecoder.java:62)
        at com.kkze.Mappy.PlacesDecoder.onCreate(PlacesDecoder.java:32)
        at android.app.Activity.performCreate(Activity.java:6221)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

还要检查 location!=null 需要 ACCESS_FINE_LOCATION 权限，这会弄乱我的应用程序，导致它始终返回为 null。

Answer 1

正如 Jon Skeet 在 cmets 中提到的，getLastKnownLocation() 方法可以并且将返回 null。主要问题是它不会提示操作系统请求新的位置锁定，而只是检查是否有来自其他应用程序的位置请求的最后一个已知位置。如果最近没有其他应用发出位置请求，那么您会收到一个空位置返回给您。

保证您实际获得位置的唯一方法是请求一个位置，这是通过调用 requestLocationUpdates() 来完成的。

传递给onLocationChanged()回调方法的位置不会为空，因为回调只发生在位置锁定成功时。

请注意，在您的应用注册位置更新的整个过程中，这将导致额外的电池消耗，因此请务必尽快取消注册位置更新。在这里，您似乎可以在第一个位置进入后立即取消注册。

此外，您可能需要考虑在此 Activity 等待位置锁定时显示进度对话框，以便向用户提供应用正在等待某事的反馈。

以下是您的代码的一般结构：

public class MainActivity extends Activity
        implements LocationListener {

    Intent intentThatCalled;
    public double latitude;
    public double longitude;
    public LocationManager locationManager;
    public Criteria criteria;
    public String bestProvider;

    String voice2text; //added

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        intentThatCalled = getIntent();
        voice2text = intentThatCalled.getStringExtra("v2txt");
        getLocation();
    }

    public static boolean isLocationEnabled(Context context)
    {
       //...............
        return true;
    }

    protected void getLocation() {
        if (isLocationEnabled(MainActivity.this)) {
            locationManager = (LocationManager)  this.getSystemService(Context.LOCATION_SERVICE);
            criteria = new Criteria();
            bestProvider = String.valueOf(locationManager.getBestProvider(criteria, true)).toString();

            //You can still do this if you like, you might get lucky:
            Location location = locationManager.getLastKnownLocation(bestProvider);
            if (location != null) {
                Log.e("TAG", "GPS is on");
                latitude = location.getLatitude();
                longitude = location.getLongitude();
                Toast.makeText(MainActivity.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
                searchNearestPlace(voice2text);
            }
            else{
                //This is what you need:
                locationManager.requestLocationUpdates(bestProvider, 1000, 0, this);
            }
        }
        else
        {
            //prompt user to enable location....
            //.................
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        locationManager.removeUpdates(this);

    }

    @Override
    public void onLocationChanged(Location location) {
        //Hey, a non null location! Sweet!

        //remove location callback:
        locationManager.removeUpdates(this);

        //open the map:
        latitude = location.getLatitude();
        longitude = location.getLongitude();
        Toast.makeText(MainActivity.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
        searchNearestPlace(voice2text);
    }

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

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }

    public void searchNearestPlace(String v2txt) {
        //.....
    }
}

Answer 2

在您的 getLocation 方法中更改此设置

if (isLocationEnabled(PlacesDecoder.this) && location != null) {
 ...
}

Answer 3

您编写了获取当前位置 (latlng) 的代码，此错误是因为您的真实 android 设备上的 gps(location) 未打开。 我打开它，它对我有用。希望有用

Answer 4

这是另一种方法来做这个你的保险丝位置概念我已经使用了这个并且对我来说是成功的 mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);

是声明融合的位置

 @SuppressWarnings( {"MissingPermission"})
private void enableLocationComponent() {
    System.out.println("on map click is here in permission///////////////");
    // Check if permissions are enabled and if not request
    if (PermissionsManager.areLocationPermissionsGranted(this)) {

        // Activate the MapboxMap LocationComponent to show user location
        // Adding in LocationComponentOptions is also an optional parameter
        LocationComponent locationComponent = mapboxMap.getLocationComponent();
        locationComponent.activateLocationComponent(this);
        locationComponent.setLocationComponentEnabled(true);
        // Set the component's camera mode
        locationComponent.setCameraMode(CameraMode.TRACKING);

        mFusedLocationClient.getLastLocation().addOnSuccessListener(this, new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        originLocation=location;
                        // Got last known location. In some rare situations this can be null.
                        if (location != null) {
                            originLocation=location;
                            System.out.println(" permission granted location is in iff ++///////////////"+location);
                        }
                    }
                });

        //originLocation = locationComponent.getLastKnownLocation();
        System.out.println("origin location is that//////////"+originLocation);


    } else {


        permissionsManager = new PermissionsManager(this);
        permissionsManager.requestLocationPermissions(this);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    permissionsManager.onRequestPermissionsResult(requestCode, permissions, grantResults);
    Toast.makeText(this, "granted", Toast.LENGTH_LONG).show();
}

@Override
public void onExplanationNeeded(List<String> permissionsToExplain) {
    Toast.makeText(this, R.string.user_location_permission_explanation, Toast.LENGTH_LONG).show();
}

@Override
public void onPermissionResult(boolean granted) {
    if (granted) {
        enableLocationComponent();
    } else {
        Toast.makeText(this, R.string.user_location_permission_not_granted, Toast.LENGTH_LONG).show();``
        finish();
    }
}

Answer 5

正如 Yash 所说，您的应用程序不请求当前位置，而是使用最后找到的位置，一个简单的解决方法对我来说适用于这个错误是，打开您的 GPS 并在您的手机上打开您的谷歌地图应用程序或模拟器查看您当前的位置，然后将其关闭。现在，当您打开当前应用程序（您正在处理）或运行它时，它不会出现此错误。为我工作。

Answer 6

发生空指针异常是因为您的应用程序不请求当前位置，而是使用上次找到的位置，只是检查您是否已打开您的位置并运行使用您当前位置的任何其他应用程序。之后，只需尝试再次运行您的项目。希望这能解决您的问题。

Answer 7

我在使用.getLastLocation() 时遇到了同样的问题。然后我使用mMap.setMyLocationEnabeled(true)，并使用.setMyLocationEnabeled(true) 启用的地图位置按钮获取GPS 位置。在那之后，下次.getLastLocation() 工作正常。我不知道确切的原因，但我认为地图上的位置按钮曾经保存了我当前的位置，下次我使用.getLastLocation() 时，它不为空，因为最后一个位置已经在那里了。