NullPointerException durante il tentativo di verificare le autorizzazioni

Question

Sto provando a verificare se l'utente ha abilitato android.Manifest.permission.ACCESS_FINE_LOCATION. Durante l'esecuzione dell'applicazione, viene visualizzato un errore NullPointerException.

pacchetto dtt.romano.rsrpechhulp;

import android.app.Activity; 
import android.content.Context; 
import android.content.IntentSender; 
import android.content.pm.PackageManager; 
import android.location.Location; 
import android.os.Bundle; 
import android.support.annotation.NonNull; 
import android.support.v4.app.ActivityCompat; 
import android.util.Log; 

import com.google.android.gms.common.ConnectionResult; 
import com.google.android.gms.common.api.GoogleApiClient; 
import com.google.android.gms.location.LocationListener; 
import com.google.android.gms.location.LocationRequest; 
import com.google.android.gms.location.LocationServices; 

public class LocationProvider extends MainActivity implements 
    GoogleApiClient.ConnectionCallbacks, 
    GoogleApiClient.OnConnectionFailedListener,LocationListener { 

public abstract interface LocationCallback { 
    public void handleNewLocation(Location location); 
} 

public static final String TAG = LocationProvider.class.getSimpleName(); 
private final static int CONNECTION_FAILURE_RESOLUTION_REQUEST = 9000; 

private LocationCallback mLocationCallback; 
private Context mContext; 
private GoogleApiClient mGoogleApiClient; 
private LocationRequest mLocationRequest; 

public LocationProvider(Context context, LocationCallback callback) { 
    mGoogleApiClient = new GoogleApiClient.Builder(context) 
      .addConnectionCallbacks(this) 
      .addOnConnectionFailedListener(this) 
      .addApi(LocationServices.API) 
      .build(); 

    mLocationCallback = callback; 

    // Create the LocationRequest object 
    mLocationRequest = LocationRequest.create() 
      .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY) 
      .setInterval(10 * 1000)  // 10 seconds, in milliseconds 
      .setFastestInterval(1 * 1000); // 1 second, in milliseconds 

    mContext = context; 
} 

public void connect() { 
    mGoogleApiClient.connect(); 
} 

public void disconnect() { 
    if (mGoogleApiClient.isConnected()) { 
     LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this); 
     mGoogleApiClient.disconnect(); 
    } 
} 

public void locationUpdate(){ 
    if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 
     ActivityCompat.requestPermissions(this, new String[]{ 
       android.Manifest.permission.ACCESS_FINE_LOCATION 
     }, 10); 
    }else{ 
     Location location = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient); 
     if (location == null) { 
      LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this); 
     } 
     else { 
      mLocationCallback.handleNewLocation(location); 
     } 
    } 
} 

@Override 
public void onConnected(Bundle bundle) { 
    Log.i(TAG, "Location services connected."); 
    locationUpdate(); 
} 

@Override 
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) { 
    switch (requestCode) { 
     case 10: 
      if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) { 
       locationUpdate(); 
      } 
      return; 
    } 
} 

@Override 
public void onConnectionSuspended(int i) { 

} 

@Override 
public void onConnectionFailed(ConnectionResult connectionResult) { 
    /* 
    * 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() && mContext instanceof Activity) { 
     try { 
      Activity activity = (Activity)mContext; 
      // Start an Activity that tries to resolve the error 
      connectionResult.startResolutionForResult(activity, CONNECTION_FAILURE_RESOLUTION_REQUEST); 
     /* 
     * Thrown if Google Play services canceled the original 
     * PendingIntent 
     */ 
     } catch (IntentSender.SendIntentException e) { 
      // Log the error 
      e.printStackTrace(); 
     } 
    } else { 
     /* 
     * If no resolution is available, display a dialog to the 
     * user with the error. 
     */ 
     Log.i(TAG, "Location services connection failed with code " + connectionResult.getErrorCode()); 
    } 
} 

@Override 
public void onLocationChanged(Location location) { 
    mLocationCallback.handleNewLocation(location); 
} 
} 

Ecco il log degli errori:

java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference               
at android.content.ContextWrapper.checkPermission(ContextWrapper.java:637) 
at android.support.v4.content.ContextCompat.checkSelfPermission(ContextCompat.java:387) 
at dtt.romano.rsrpechhulp.LocationProvider.onConnected(LocationProvider.java:68) 
at com.google.android.gms.common.internal.zzk.zzk(Unknown Source) 
at com.google.android.gms.common.api.internal.zzj.zzi(Unknown Source) 
at com.google.android.gms.common.api.internal.zzh.zzpx(Unknown Source) 
at com.google.android.gms.common.api.internal.zzh.onConnected(Unknown Source) 
at com.google.android.gms.common.api.internal.zzl.onConnected(Unknown Source) 
at com.google.android.gms.common.api.internal.zzc.onConnected(Unknown Source) 
at com.google.android.gms.common.internal.zzj$zzg.zzqL(Unknown Source) 
at com.google.android.gms.common.internal.zzj$zza.zzc(Unknown Source) 
at com.google.android.gms.common.internal.zzj$zza.zzw(Unknown Source) 
at com.google.android.gms.common.internal.zzj$zzc.zzqN(Unknown Source) 
at com.google.android.gms.common.internal.zzj$zzb.handleMessage(Unknown Source) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

if (ActivityCompat.checkSelfPermission((Activity)mContext, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) { 
    ActivityCompat.requestPermissions((Activity)mContext, new String[]{ 
      android.Manifest.permission.ACCESS_FINE_LOCATION 
    }, 10); 

tenta di utilizzare (Attività) mContext al posto di questo. potrebbe essere il tuo aiuto