public class DemoBlock extends BlockWithEntity {
    [...]
    @Override
    protected ItemActionResult onUseWithItem(ItemStack stack, BlockState state, World world, BlockPos pos, PlayerEntity player, Hand hand, BlockHitResult hit) {
        if (world.isClient) return ActionResult.SUCCESS;
        
        if (!(world.getBlockEntity(pos) instanceof DemoBlockEntity blockEntity)) {
            return ItemActionResult.PASS_TO_DEFAULT_BLOCK_INTERACTION;
        }

        if (!player.getStackInHand(hand).isEmpty()) {
            // 检查第一个开放槽位是什么，并从玩家手中将物品放入
            if (blockEntity.getStack(0).isEmpty()) {
                // 将玩家持有的物品堆放入物品栏
                blockEntity.setStack(0, player.getStackInHand(hand).copy());
                // 从玩家手中移除物品堆
                player.getStackInHand(hand).setCount(0);
            } else if (blockEntity.getStack(1).isEmpty()) {
                blockEntity.setStack(1, player.getStackInHand(hand).copy());
                player.getStackInHand(hand).setCount(0);
            } else {
                // 如果物品栏满，提醒玩家
                player.sendMessage(Text.literal("物品栏满！第一个槽位是")
                    .append(blockEntity.getStack(0).getName())
                    .append("，第二个槽位是")
                    .append(blockEntity.getStack(1).getName()));
            }
        } 
        return ItemActionResult.SUCCESS;
    }
}