public class PackContainer extends Container {

    private ItemPack itemPack;

    public PackContainer(IInventory playerInventory) {
        addOwnSlots();
        addPlayerSlots(playerInventory);
    }

    private void addPlayerSlots(IInventory playerInventory) {
        // Slots for the main inventory
        for (int row = 0; row < 3; ++row) {
            for (int col = 0; col < 9; ++col) {
                int x = 9 + col * 18;
                int y = row * 18 + 70;
                this.addSlotToContainer(new Slot(playerInventory, col + row * 9 + 10, x, y));
            }
        }

        // Slots for the hotbar
        for (int row = 0; row < 9; ++row) {
            int x = 9 + row * 18;
            int y = 58 + 70;
            this.addSlotToContainer(new Slot(playerInventory, row, x, y));
        }
    }

    private ItemStackHandler itemStackHandler = new ItemStackHandler(9);

    private void addOwnSlots() {
        IItemHandler itemHandler = itemStackHandler;
        int x = 9;
        int y = 6;

        // Add our own slots
        int slotIndex = 0;
        for (int i = 0; i < itemHandler.getSlots(); i++) {
            addSlotToContainer(new SlotItemHandler(itemHandler, slotIndex, x, y));
            slotIndex++;
            x += 18;
        }
    }

    @Nullable
    @Override
    public ItemStack transferStackInSlot(EntityPlayer playerIn, int index) {
        ItemStack itemstack = null;
        Slot slot = this.inventorySlots.get(index);

        if (slot != null && slot.getHasStack()) {
            ItemStack itemstack1 = slot.getStack();
            itemstack = itemstack1.copy();

            if (index < 9) {
                if (!this.mergeItemStack(itemstack1, 9, this.inventorySlots.size(), true)) {
                    return null;
                }
            } else if (!this.mergeItemStack(itemstack1, 0, 9, false)) {
                return null;
            }

            if (itemstack1.isEmpty()) {
                slot.putStack(ItemStack.EMPTY);
            } else {
                slot.onSlotChanged();
            }
        }

        return itemstack;
    }

    @Override
    public boolean canInteractWith(EntityPlayer playerIn) {
        // TODO Auto-generated method stub
        return true;
    }
}