[1.16] Please help...... Creating a container that can switch inventory of different capability items

Help me. I've been trying it for about two days, but I don't know. Currently the code is below. If you open the inventory with the backpack equipped and close it after operating the backpack slot, it will be saved correctly. However, if you open it with it equipped, remove the backpack, re-equip it, close the slot after operating it, the operation is not saved. Here's what I want to implement: What should I do to do that? Where should I fix it and which method should I use? I need help.

1. The backpack slot is active when the player is equipped with a backpack.
2. The same applies when the player equips / removes the backpack in the inventory screen. At that time, the slot (the item operation performed in the backpack inventory) is saved correctly.
3. With the above, it is possible to put on and take off multiple backpack items (that is, each has a different inventory) in the inventory.

AbstractUMUPlayerContainer addsslot()s vanilla player inventory slots.

public class BelongingsUMUPlayerContainer extends AbstractUMUPlayerContainer {

	private static final UMUEquipmentSlotType[] VALID_EQUIPMENT_SLOTS = new UMUEquipmentSlotType[]{
			UMUEquipmentSlotType.HEAD, UMUEquipmentSlotType.CHEST, UMUEquipmentSlotType.LEGS, UMUEquipmentSlotType.FEET
	};
	private static final UMUEquipmentSlotType[] VALID_RING_SLOTS = new UMUEquipmentSlotType[]{
			UMUEquipmentSlotType.MAINRING1, UMUEquipmentSlotType.MAINRING2, UMUEquipmentSlotType.OFFRING1, UMUEquipmentSlotType.OFFRING2
	};
	private static final UMUEquipmentSlotType[] VALID_MISCELLANEOUS_SLOTS = new UMUEquipmentSlotType[]{
			UMUEquipmentSlotType.ENCYCLOPEDIA, UMUEquipmentSlotType.MAP
	};

	public BelongingsUMUPlayerContainer(int id, PlayerInventory playerInventory, PacketBuffer extraData) {
		this(UMUContainers.BELONGING_INVENTORY.get(), id, playerInventory, playerInventory.player);
	}

	public BelongingsUMUPlayerContainer(ContainerType<?> type, int id, PlayerInventory playerInventory, PlayerEntity player) {
		super(type, id, playerInventory, player);

		// index : 36 - 39
		for (int i = 0; i < 4; i++) {
			this.addSlot(new EquipmentSlot(playerInventory, 39 - i, 186, 18 + i * 18, VALID_EQUIPMENT_SLOTS[i]));
		}
		this.addSlot(new OffhandSlot(playerInventory, 40, 255, 72));
		this.addSlot(new EquipmentSlot(playerInventory, 41, 293, 27, UMUEquipmentSlotType.NECKLACE));
		// index : 42 - 45
		for (int iU = 0; iU < 2; iU++) {
			for (int iV = 0; iV < 2; iV++) {
				this.addSlot(new EquipmentSlot(playerInventory, 42 + iU * 2 + iV, 282 + iU * 18 + 4, 48 + iV * 18, VALID_RING_SLOTS[iU * 2 + iV]));
			}
		}
		for (int i = 0; i < 2; i++) {
			this.addSlot(new EquipmentSlot(playerInventory, 46 + i, 330, 72 + i * 18, VALID_MISCELLANEOUS_SLOTS[i]));
		}
//		for (int iV = 0; iV < 4; iV++) {
//			for (int iU = 0; iU < 9; iU++) {
//				//this.addSlot(new BackpackSlot(new ItemStackHandler(36), iU + iV * 9, 8 + iU * 18, 18 + iV * 18, Minecraft.getInstance().player, iV + 1));
//			}
//		}
		this.initBackpackSlots();
	}

	private void initBackpackSlots() {
		for (int iV = 0; iV < 4; iV++) {
			for (int iU = 0; iU < 9; iU++) {
				IItemHandler itemHandler = new ItemStackHandler(36);
				if (UMUEntityUtil.hasBackpack(this.player)) {
					itemHandler = this.player.getItemStackFromSlot(EquipmentSlotType.CHEST)
							.getCapability(CapabilityItemHandler.ITEM_HANDLER_CAPABILITY).orElse(new ItemStackHandler(36));
				}
				this.addSlot(new BSlot(itemHandler, iU + iV * 9, 8 + iU * 18, 18 + iV * 18, this.player, iV + 1));
			}
		}
	}

	@Override
	public ItemStack slotClick(int slotId, int dragType, ClickType clickTypeIn, PlayerEntity player) {
		if (slotId == 38) {
			//this.inventorySlots.subList(48, 83).forEach(s -> ((BackpackSlot) s).onEquipOrRemoveBackpack());
			player.openContainer = new BelongingsUMUPlayerContainer(this.windowId, player.inventory, null);
		}

		return super.slotClick(slotId, dragType, clickTypeIn, player);
	}

	public class BSlot extends SlotItemHandler {
		private final PlayerEntity player;
		private final int size;

		public BSlot(IItemHandler itemHandler, int index, int xPosition, int yPosition, PlayerEntity player, int size) {
			super(itemHandler, index, xPosition, yPosition);
			this.player = player;
			this.size = size;
		}

		@Override
		public boolean isEnabled() {
			if (UMUEntityUtil.hasBackpack(player)) {
				return UMUEntityUtil.getBackpackSize(Minecraft.getInstance().player) >= size;
			}

			return false;
		}
	}
}