Passing Array Adapter via Constructor | ListView

Question

I am trying to use adapter from my LocationsFragment.class into my DeviceAdmin.class to add two Strings say mylatitude and mylongitude to my ListView. I am going through Constructor Method. But it seems to return null, whenever I call adapter.add(mylatitude + " " + mylongitude); in my DeviceAdmin.class

  java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ArrayAdapter.add(java.lang.Object)' on a null object reference
        at com.ayush.trixter.ui.captures.DeviceAdmin$1.onLocationChanged(DeviceAdmin.java:103)

Line 103 is : adapter.add("Latitude: " + mylat + "Longitude: " + mylon);

DeviceAdmin.class


import android.Manifest;
import android.annotation.SuppressLint;
import android.app.admin.DeviceAdminReceiver;
import android.app.admin.DevicePolicyManager;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Paint;
import android.graphics.SurfaceTexture;
import android.hardware.Camera;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraManager;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Build;
import android.os.Looper;
import android.os.UserHandle;
import android.util.Log;
import android.util.SparseIntArray;
import android.view.ContextThemeWrapper;
import android.view.Surface;
import android.view.View;
import android.widget.Adapter;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.core.content.PermissionChecker;

import com.ayush.trixter.R;
import com.ayush.trixter.ui.locations.LocationFragment;
import com.google.android.gms.location.LocationCallback;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.material.snackbar.Snackbar;
import com.google.firebase.database.FirebaseDatabase;

import java.util.ArrayList;

public class DeviceAdmin extends DeviceAdminReceiver
{
    private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
    public CameraManager cam;
    LocationManager locationManager;
    final String TAG = "[Trixter]";
    DevicePolicyManager mgr;
    FirebaseDatabase db;
    public boolean mTracking = false;
    public ArrayList<String> listItems=new ArrayList<>();
    LocationFragment lf = new LocationFragment();
    ArrayAdapter<String> adapter = lf.adapter;



    @Override
    public void onPasswordFailed(@NonNull Context ctx, @NonNull Intent intent, @NonNull UserHandle user) {
        super.onPasswordFailed(ctx, intent, user);
        cam = (CameraManager) ctx.getSystemService(Context.CAMERA_SERVICE);
        mgr = (DevicePolicyManager) ctx.getSystemService(Context.DEVICE_POLICY_SERVICE);

        Log.d(TAG,"PasswordFailed");
        int pwdfailcount = mgr.getCurrentFailedPasswordAttempts();

        if(pwdfailcount==3)
        {
            takeSnapShots();
            getloc(ctx);

        }
    }

    public void getloc(Context ctx)
    {
        locationManager = (LocationManager) ctx.getSystemService(Context.LOCATION_SERVICE);
        Criteria criteria = new Criteria();
        String provider =  locationManager.getBestProvider(criteria,true);
        boolean gps_enabled = false;
        boolean network_enabled = false;

        try
        { gps_enabled =   locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); }
        catch (Exception e) {}
        try { network_enabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);} catch (Exception e) {}

        if(PermissionChecker.checkSelfPermission(ctx, Manifest.permission.ACCESS_COARSE_LOCATION) == PermissionChecker.PERMISSION_GRANTED && PermissionChecker.checkSelfPermission(ctx,Manifest.permission.ACCESS_FINE_LOCATION) == PermissionChecker.PERMISSION_GRANTED) {
            if(gps_enabled == true && network_enabled ==true) {
                locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, new LocationListener() {
                    @Override
                    public void onLocationChanged(@NonNull Location loc) {
                        double mylat = loc.getLatitude();
                        double mylon = loc.getLongitude();
                        double myacc = loc.getAccuracy();
                        double time = loc.getTime();
                        double myalt = loc.getAltitude();
                        Log.d("[TrixterLocation]", "The Latitude:- " + mylat + "\nThe Longitude:- " + mylon + "\nThe Altitude:- " + myalt + "\n The Accuracy" + myacc + "\nThe Time:- " + time);
                        adapter.add("Latitude: " + mylat + "Longitude: " + mylon);
                    }
                });
            }
            else
            {
                Toast.makeText(ctx, "Location is not enabled", Toast.LENGTH_SHORT).show();
                Log.d("[Trixter] ","Error: Location or Internet Not Enabled");
            }
        }

    }



    private void takeSnapShots()
    {

    }





}

LocationsFragment.class

package com.ayush.trixter.ui.locations;

import android.content.Context;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.ListFragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.ayush.trixter.R;
import com.ayush.trixter.ui.captures.DeviceAdmin;

import java.util.ArrayList;

public class LocationFragment extends ListFragment {

    ListView loclst;
    LocationManager locationManager;
    public ArrayList<String> listItems=new ArrayList<>();
    public ArrayAdapter<String> adapter = (ArrayAdapter<String>) getListAdapter();

    public LocationFragment()
    {

    }
    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.fragment_locations, container, false);
            loclst = root.findViewById(android.R.id.list);
            Context context = getActivity();
            locationManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
            adapter = new ArrayAdapter<String>(getActivity(),   android.R.layout.simple_list_item_2 , listItems);
            loclst.setAdapter(adapter);

          return root;
    }

}

According to me:- It would return null since ArrayAdapter is not initialized and only gets initialized when the Fragment Opens i.e. onCreateView()

But I am not able to find a solution to make it work. Also if anyone has a better idea to do this more easily please tell.

Ofek · Accepted Answer · 2020-08-13 11:54:55Z

1

It wont work because you're creating a new LocationFramgent on your DeviceAdmin class.

What you need to do is access the actual LocationFragment.

To answer you properly i need to knwo:

Where is the fragment being created from?

And where do you call getLoc method?

answered Aug 13, 2020 at 11:54

Ofek

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4 Comments

Ayush Over a year ago

Where is the fragment being created from? Answer:- from home.class not the main activity. This is the code home.class

Ayush Over a year ago

And where do you call getLoc method? Answer: it is called on onPasswordFailed of DeviceAdmin class if password fail count is equal to 3 . [click me for code method] (hastebin.com/rihebomijo.java)

Ofek Over a year ago

I see you are using a navcontroller. To fix this, where ever you are creating the DeviceAdmin instance also pass a reference to the navcontroller so you can get the actual location fragment and call the add function in the adapter of the real location fragment.

Ayush Over a year ago

Thanks for the answer. I request you to please be more specific like by providing an example . I am kind off new to app development.

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