Image Adapter not able to initialize image Views

private void addSelectedCardToGlobalUserBox(int position) {
...
}

    public void addInteger(Integer integer) {
        adapter.addDrawableToList(integer);
    }

public class MainActivity extends AppCompatActivity {

    private Toolbar mToolbar;

    // NavMenu member vars
    private DrawerLayout mDrawerLayout;
    private NavigationView navigationView;
    private ActionBarDrawerToggle mToggle; // Button for toggling the side menu

    // Keeps the position of the previously selected menu item(0 : Home)
    int position = 0;

    // Declaring our dialog
    ImportantDialogFragment dialogFragment = new ImportantDialogFragment();

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

        // Showing the disclaimer dialog every time the app starts
        dialogFragment.show(getSupportFragmentManager(),"IMPORTANT_NOTICE");

        mDrawerLayout = findViewById(R.id.drawerLayout);
        navigationView = findViewById(R.id.nav_view);
        mToggle = new ActionBarDrawerToggle(this,mDrawerLayout,R.string.drawer_open,R.string.drawer_closed); // Instantiating our button


        mToolbar = findViewById(R.id.navActionBar);
        setSupportActionBar(mToolbar); // check quick doq
        getSupportActionBar().setDisplayShowTitleEnabled(false);
        mToolbar.setTitle("");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        // Sets the default selected menu item, to the Home item
        navigationView.getMenu().findItem(R.id.nav_home).setChecked(true);

        // Used to help on check and uncheck menu items when the user clicks on them
        final List<MenuItem> items = new ArrayList<>();
        Menu menu;
        menu = navigationView.getMenu();

        // Fill the list with all the menu items
        for(int i=0; i<menu.size();i++) {
            items.add(menu.getItem(i));
        }

       // Toast.makeText(this, "size:" + items.size(), Toast.LENGTH_SHORT).show();

        // Set the default starting screen to the mainScreen
        FragmentManager startingScreenManager = getSupportFragmentManager();
        FragmentTransaction startingScreenTransaction = startingScreenManager.beginTransaction();

        MainScreenFragment fragment = new MainScreenFragment();
        startingScreenTransaction.add(R.id.FrameLayoutContainer, fragment);
        startingScreenTransaction.commit();

        final UserBoxGLBFragment glbFragment = new UserBoxGLBFragment();
        // When an item inside the NavView gets clicked, then handle the event...
        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {

            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {

            // Initializing these vars again for use in this inner class
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

            // Replace the main Fragment in this activity based on the menu item selected
                switch (item.getItemId()) {
                    case R.id.nav_home:
                        MainScreenFragment mainScreenFragment = new MainScreenFragment();
                        fragmentTransaction.replace(R.id.FrameLayoutContainer,mainScreenFragment);
                        fragmentTransaction.commit();
                        break;
                    case R.id.nav_UserBoxGLB:
                        //UserBoxGLBFragment glbFragment = new UserBoxGLBFragment();
                        fragmentTransaction.replace(R.id.FrameLayoutContainer,glbFragment);
                        fragmentTransaction.commit();
                        break;
                    case R.id.nav_UserBoxJP:
                        break;
                    case R.id.nav_events:
                        Toast.makeText(MainActivity.this, "Events are not available yet! Sorry", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.nav_feedback:
                        composeEmail(emails,"Feedback", "[Your message here]");
                        break;
                    case R.id.nav_contact_us:
                        composeEmail(emails,"Contact Us", "[Your message here]");
                        break;
                    case R.id.nav_website:
                        // Open the website's URL in a browser window
                        Intent intent = new Intent();
                        intent.setAction(Intent.ACTION_VIEW);
                        intent.addCategory(Intent.CATEGORY_BROWSABLE);
                        intent.setData(Uri.parse("http://www.google.com"));
                        startActivity(intent);
                        break;
                    case R.id.nav_about:
                        Intent aboutIntent = new Intent(MainActivity.this, AboutPageActivity.class);
                        startActivity(aboutIntent);
                        break;
                    default:
                        return onNavigationItemSelected(item);
                }
                items.get(position).setChecked(false);
                item.setChecked(true);
                mDrawerLayout.closeDrawers();
                return false;
            }
        });

        mDrawerLayout.addDrawerListener(mToggle);
        // Set the hamburger icon's color
        mToggle.getDrawerArrowDrawable().setColor(getResources().getColor(R.color.NavActionBarTextColor));
        mToggle.syncState();
    }

    // When an item from the Action Bar gets tapped, then...
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        return mToggle.onOptionsItemSelected(item) || onOptionsItemSelected(item);
    }

    private String[] emails = {"SPDesignsOfficial@outlook.com"};

    /**
     * Send an email to the @adress with a @subject
     * @param addresses The email adress(es) to send the email to
     * @param subject The email's subject
     */
    public void composeEmail(String[] addresses, String subject, String message) {
        Intent intent = new Intent(Intent.ACTION_SENDTO);
        intent.setData(Uri.parse("mailto:")); // only email apps should handle this
        intent.putExtra(Intent.EXTRA_EMAIL, addresses);
        intent.putExtra(Intent.EXTRA_SUBJECT, subject);
        intent.putExtra(Intent.EXTRA_TEXT,message);
        if (intent.resolveActivity(getPackageManager()) != null) {
            startActivity(intent);
        }
    }
}

public class ImageAdapter extends BaseAdapter {
    Context mContext;

    public ImageAdapter(Context c) {
        mContext = c;
    }

    @Override
    public int getCount() {
        return mThumbIds.length;
    }

    @Override
    public Object getItem(int i) {
        return null;
    }

    @Override
    public long getItemId(int i) {
        return 0;
    }

    // create a new ImageView for each item referenced by the Adapter
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        // If it's not recycled, initialize some attributes
        if (convertView == null) {
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(225, 225));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }
        imageView.setImageResource(mThumbIds[position]);
        return imageView;
    }

    public Integer getmThumbIds(int index) {
        return mThumbIds[index];
    }

    // References to our images
    private Integer[] mThumbIds = {
            R.drawable.beyondthe_ferocious_flash_majin_vegeta_icon
//            R.mipmap.full_tilt_kamehameha_super_saiyan2_gohan_youth_icon,
//            R.mipmap.merciless_condemnation_goku_black_super_saiyan_rose_and_zamasu_icon,
//            R.mipmap.everlasting_legend_super_saiyan_goku_icon,
//            R.mipmap.indestructible_saiyan_evil_legendary_super_saiyan_broly_icon
    };
}

public class MainScreenFragment extends Fragment {

    // Main Grid View
    GridView gridView;

    public MainScreenFragment() {
        // Required empty public constructor
    }

    // Create a Context Menu when an item in the GridView is long-pressed
    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);
        menu.setHeaderTitle("Card Options");
        //AdapterView.AdapterContextMenuInfo cmi = (AdapterView.AdapterContextMenuInfo) menuInfo;
        menu.add(1,v.getId(),0, "Add Card to GLB");
        menu.add(2,v.getId(),0,"Add Card to JP");
    }

    // When an item in the context menu gets selected, call a method
    @Override
    public boolean onContextItemSelected(MenuItem item) {

        // Get some extra info about the contextMenu
        AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();

        int position = info.position; // clicked view's position

        if(item.getTitle().equals("Add Card to GLB")) {
            addCardMessage(position, "added to GLB");
            addSelectedCardToGlobalUserBox(position);
        } else if (item.getTitle().equals("Add Card to JP")) {
            addCardMessage(position , "added to JP");
        } else
        {
            return false;
        }
        return false;
    }

    /**
     * Creates a snackbar message, telling the user which card was added to which box
     * @param id The position of the chosen card
     * @param text Defines into which User Box the card was added
     */
    private void addCardMessage(int id, String text) {
          final Snackbar snackbar = Snackbar.make(gridView, id + " " + text ,Snackbar.LENGTH_LONG);

          snackbar.setAction("Dismiss", new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                snackbar.dismiss();
            }
        });
        snackbar.setActionTextColor(Color.MAGENTA);
        snackbar.show();
    }


    UserBoxGLBFragment fragment = new UserBoxGLBFragment();
    private void addSelectedCardToGlobalUserBox(int position) {
        ImageAdapter imageAdapter = new ImageAdapter(getContext());
        fragment.addInteger(imageAdapter.getmThumbIds(0)); // pass the Drawable's Integer value to the fragmnet
        Toast.makeText(getActivity(), "Selected icon: " + imageAdapter.getmThumbIds(position), Toast.LENGTH_SHORT).show();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_main_screen, container, false);

        gridView = view.findViewById(R.id.gridViewLayout);
        gridView.setAdapter(new ImageAdapter(getContext())); // used to set the contents of the GridView-in this case images-
        registerForContextMenu(gridView);

        // When an item from the GridView gets clicked
        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                // Create a new Intent...
                Toast.makeText(getActivity(), "Position: " + position, Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(getContext(),CardViewActivity.class);
                intent.putExtra("Card Index",position);
                intent.putExtra("SCREEN_WIDTH",1080);
                startActivity(intent);
            }
        });
        return view;
    }

}

public class UserBoxGLBFragment extends Fragment {

    GridView globalGridView;
    UserBoxGlbImageAdapter adapter = new UserBoxGlbImageAdapter(getContext());

    public UserBoxGLBFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_user_box_glb, container, false);
        globalGridView = view.findViewById(R.id.userBoxGlbGridView);
        globalGridView.setAdapter(adapter);
        return view;
    }

    public void addInteger(Integer integer) {
        adapter.addDrawableToList(integer);
    }
}

public class UserBoxGlbImageAdapter extends BaseAdapter {

    private Context mContext;

    private List<Integer> mGLBIcons = new ArrayList<>();

    public UserBoxGlbImageAdapter(Context c) {
        mContext = c;
    }

    public List<Integer> getIcons() {
        return mGLBIcons;
    }

    @Override
    public int getCount() {
        return mGLBIcons.size();
    }

    @Override
    public Object getItem(int i) {
        return mGLBIcons.get(i);
    }

    @Override
    public long getItemId(int i) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        // If it's not recycled, initialize some attributes
        if (convertView == null) {
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(225, 225));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }
         //Drawable drbl = mContext.getResources().getDrawable(mGLBIcons.get(0));
        Toast.makeText(mContext, "Size:" + getCount(), Toast.LENGTH_SHORT).show();
        imageView.setImageResource(getIcons().get(0));
        return imageView;
    }

    public void addDrawableToList(Integer integer) {
        mGLBIcons.add(integer);
        notifyDataSetChanged();
    }
}