java如何使用在安卓中另一个名为“活动B”的活动中的“活动a”的情况下定义的方法？

Question

我有“活动A”和“活动B”。在“活动A”中，底部导航栏工作正常。现在，我需要“活动A”的相同底部导航栏才能在“活动B”中工作。我在“活动B”中创建了相同的底部导航栏布局，并试图导入“活动A”的功能，但应用程序崩溃了好几次。感谢您的帮助

活动A:

          switch (item.getItemId()) {
        case R.id.action_picture_from_gallery: {
            if (PermissionChecker.doIfPermissionGranted(this))
            {
                Intent i = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
                ActivityUtils.get(this).animateToActivity(i, false, REQUEST_LOAD_GALLERY_IMAGE);
            }
            return true;

        }
        case R.id.action_picture_from_camera: {
            showCameraDialog();
            //intent = new Intent(安卓.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            //startActivityForResult(intent, 9);
            //Toast.makeText(app, "Image From Camera", Toast.LENGTH_SHORT).show();
            return true;
        }


        case R.id.nav_mode_create: {
       Intent i = new Intent(MainActivity.this, ItemsActivity.class);
            startActivity(i);
            //selectedfragment=new HomeFragment();
            break;
        }
        case R.id.nav_mode_favs: {
            _currentMainMode = 1;
            imageList = new ArrayList<>();
            _emptylistText.setText(R.string.no_favourites_description__appspecific);
            for (String fav : app.settings.getFavoriteMemeTemplates()) {
                MemeData.Image img = MemeData.findImage(new File(fav));
                if (img != null) {
                    imageList.add(img);
                }
            }
            _toolbar.setTitle(R.string.favs);
            break;
        }
        case R.id.nav_mode_saved: {
            _currentMainMode = 2;
            _emptylistText.setText(R.string.no_memes_saved_description__appspecific);

            if (PermissionChecker.hasExtStoragePerm(this)) {
                File folder = AssetUpdater.getMemesDir(AppSettings.get());
                folder.mkdirs();
                imageList = MemeData.getCreatedMemes();
            }
            _toolbar.setTitle(R.string.saved);
            break;
        }

        case R.id.nav_mode_hidden: {
            _currentMainMode = 3;
            imageList = new ArrayList<>();

            for (String hidden : app.settings.getHiddenMemesTemplate()) {
                MemeData.Image image = MemeData.findImage(new File(hidden));
                if (image != null) {
                    imageList.add(image);
                }
            }
            _toolbar.setTitle(R.string.hidden);
            break;
        }



        case R.id.nav_more: {

            _currentMainMode = 4;
            _toolbar.setTitle(R.string.more);
            break;

        }


    }

活动B:

         public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) 
   {
            List<MemeData.Image> imageList = null;
            switch(menuItem.getItemId())
            {
                case R.id.nav_mode_create:
            //Here how can i use method of "Activity A"

                    break;


                case R.id.nav_mode_favs:
       //Here how can i use method of "Activity A"

                    break;

                case R.id.nav_mode_saved:

         //Here how can i use method of "Activity A"
                    break;




                case R.id.nav_mode_hidden:
                   //Here how can i use method of "Activity A"
                    break;

               case R.id.nav_more:
                  //Here how can i use method of "Activity A"
                    break;
            }
            return true;
        }