osmdroid PreferenceManager.getDefaultSharedPreferences(ctx)

Error 

osmdroid Attempt to invoke virtual method 'java.lang.String java.io.File.getAbsolutePath()' on a null object reference

 Solution:

Change From:

// This will casuse error
Context ctx = getApplicationContext();
Configuration.getInstance().load(ctx, PreferenceManager.getDefaultSharedPreferences(ctx));

To

Context ctx = getApplicationContext();
Configuration.getInstance().setUserAgentValue(ctx.getPackageName());

Example

import android.content.Context;
import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

import org.osmdroid.api.IMapController;
import org.osmdroid.config.Configuration;
import org.osmdroid.tileprovider.tilesource.TileSourceFactory;
import org.osmdroid.util.GeoPoint;
import org.osmdroid.views.MapView;



public class MapActivity extends AppCompatActivity {

    MapView map = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //It must added, otherwise the map will not be shown
        //load/initialize the osmdroid configuration, this can be done

        // This will casuse error
        //Context ctx = getApplicationContext();
        //Configuration.getInstance().load(ctx, PreferenceManager.getDefaultSharedPreferences(ctx));

        Context ctx = getApplicationContext();
        Configuration.getInstance().setUserAgentValue(ctx.getPackageName());

        //setting this before the layout is inflated is a good idea
        //it 'should' ensure that the map has a writable location for the map cache, even without permissions
        //if no tiles are displayed, you can try overriding the cache path using Configuration.getInstance().setCachePath
        //see also StorageUtils
        //note, the load method also sets the HTTP User Agent to your application's package name, abusing osm's tile servers will get you banned based on this string
        setContentView(R.layout.activity_map);

        map = (MapView) findViewById(R.id.mapview);
        map.setTileSource(TileSourceFactory.MAPNIK);

        IMapController mapController = map.getController();
        mapController.setZoom(18);
        //GeoPoint startPoint = new GeoPoint(52.516181, 13.376935);

        GeoPoint startPoint = new GeoPoint(22.3193, 114.1694);
        mapController.setCenter(startPoint);

    }
}

Reference:

E/AndroidRuntime: FATAL EXCEPTION: main

    Process: com.example.taxibeta1, PID: 23541

    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.taxibeta1/com.example.taxibeta1.MapActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.io.File.getAbsolutePath()' on a null object reference

        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)

        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)

        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)

        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)

        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)

        at android.os.Handler.dispatchMessage(Handler.java:106)

        at android.os.Looper.loop(Looper.java:223)

        at android.app.ActivityThread.main(ActivityThread.java:7656)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.io.File.getAbsolutePath()' on a null object reference

        at org.osmdroid.config.DefaultConfigurationProvider.load(DefaultConfigurationProvider.java:337)

        at com.example.taxibeta1.MapActivity.onCreate(MapActivity.java:29)

        at android.app.Activity.performCreate(Activity.java:8000)

        at android.app.Activity.performCreate(Activity.java:7984)

        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)

        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)

        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 

        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 

        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 

        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 

        at android.os.Handler.dispatchMessage(Handler.java:106) 

        at android.os.Looper.loop(Looper.java:223) 

        at android.app.ActivityThread.main(ActivityThread.java:7656)