我的应用程序有点问题。当我在手机中使用它时，它可以完全正常工作，但当我按下一个带有＆＃34; finish()＆＃34;命令它停止。当我试图重新打开它时，它表示它有一个零点异常。而且我不知道为什么。这是带有例外的代码。
public class MapAlertService extends Service {
public static final String HOME_LONGITUDE = "HOME_LONGITUDE";
public static final String HOME_LATITUDE = "HOME_LATITUDE";
public static final String USER_NUMBER = "USER_NUMBER";
private final String PROX_ALERT = "com.emmanuilvaresis.oldiefinder.ProximityAlert";
SharedPreferences prefs;
Context context;
double lat = 0;
double lng = 0;
double hlat = 0;
double hlng = 0;
float radius = 80f; // meters
long expiration = -1; // do not expire
private LocationManager locationManager;
PackageManager packageManager;
static int flag = 0;
@Override
public void onCreate(){
context = getApplicationContext();
Toast.makeText(context, "map alert service Created", Toast.LENGTH_LONG).show();
prefs = PreferenceManager.getDefaultSharedPreferences(context);
LocationManager locationManager;
String svcName = Context.LOCATION_SERVICE;
locationManager = (LocationManager) getSystemService(svcName);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
criteria.setPowerRequirement(Criteria.POWER_LOW);
criteria.setAltitudeRequired(false);
criteria.setBearingRequired(false);
criteria.setSpeedRequired(false);
criteria.setCostAllowed(true);
String provider = locationManager.getBestProvider(criteria, true);
PackageManager packageManager = getPackageManager();
if (packageManager.checkPermission(android.Manifest.permission.ACCESS_FINE_LOCATION, getPackageName())
== PackageManager.PERMISSION_GRANTED){
Location l = locationManager.getLastKnownLocation(provider);
getCoordinates(l);
locationManager.requestLocationUpdates(provider, 10, 10, locationListener);
}
}
private void getCoordinates(Location l){
if (l != null) {
lat = l.getLatitude();
lng = l.getLongitude();
}
double templat, templng;
templat = prefs.getFloat(HOME_LATITUDE, 0);
templng = prefs.getFloat(HOME_LONGITUDE, 0);
if((hlat != templat) && (hlng != templng)){
hlat = templat;
hlng = templng;
if((hlat!=0) && (hlng!=0)){
addProximityAlert(hlat, hlng);
}
}
}
private final LocationListener locationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
getCoordinates(location);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
};
private void addProximityAlert(double latitude, double longitude) {
if (packageManager.checkPermission(android.Manifest.permission.ACCESS_FINE_LOCATION, getPackageName())
== PackageManager.PERMISSION_GRANTED){
Intent intent = new Intent(PROX_ALERT);
PendingIntent proximityIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
locationManager.addProximityAlert(latitude, longitude, radius, expiration, proximityIntent);
IntentFilter filter = new IntentFilter(PROX_ALERT);
registerReceiver(new MapAlertReceiver(), filter);
}
}
public class MapAlertReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
final String key = LocationManager.KEY_PROXIMITY_ENTERING;
final Boolean entering = intent.getBooleanExtra(key, false);
if (!entering){
Toast.makeText(context,"You are exiting the safe circle", Toast.LENGTH_SHORT).show();
if (flag == 0){
String msgBody = "The user is 1km far from his house";
String number = prefs.getString(USER_NUMBER, "0");
try {
if ((lat!=0) && (lng!=0) && !(number.equals("0"))){
SmsManager smsManager = SmsManager.getDefault();
smsManager.sendTextMessage(number, null, msgBody, null, null);
Toast.makeText(context, "Message sent", Toast.LENGTH_SHORT).show();
}
else {
Toast.makeText(context, "Message didn't sent", Toast.LENGTH_SHORT).show();
}
} catch (Exception e) {
e.printStackTrace();
}
flag = 1;
}
}
else{
Toast.makeText(context,"You are entering the safe circle", Toast.LENGTH_SHORT).show();
flag = 0;
}
}
}
@Override
public IBinder onBind(Intent intent) {
// TODO: Return the communication channel to the service.
throw new UnsupportedOperationException("Not yet implemented");
}
}
logcat文件：
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: FATAL EXCEPTION: main
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: Process: com.emmanuilvaresis.oldiefinder, PID: 28905
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: java.lang.RuntimeException: Unable to create service com.emmanuilvaresis.oldiefinder.MapAlertService: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.pm.PackageManager.checkPermission(java.lang.String, java.lang.String)' on a null object reference
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.handleCreateService(ActivityThread.java:3160)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.access$1900(ActivityThread.java:177)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.os.Looper.loop(Looper.java:145)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5944)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.pm.PackageManager.checkPermission(java.lang.String, java.lang.String)' on a null object reference
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.emmanuilvaresis.oldiefinder.MapAlertService.addProximityAlert(MapAlertService.java:102)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.emmanuilvaresis.oldiefinder.MapAlertService.getCoordinates(MapAlertService.java:77)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.emmanuilvaresis.oldiefinder.MapAlertService.onCreate(MapAlertService.java:60)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.handleCreateService(ActivityThread.java:3150)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.access$1900(ActivityThread.java:177)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.os.Looper.loop(Looper.java:145)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5944)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389)
11-15 22:10:31.779 28905-28905/com.emmanuilvaresis.oldiefinder E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184)
答案 0 :(得分：3)
onCreate中的局部变量packageManager中的隐藏了声明为成员类的那个，使其初始化，并导致NPE addProximityAlert。内部onCreate更改
PackageManager packageManager = getPackageManager();
与
packageManager = getPackageManager();