Assuming any inventory changes are the result of actions such as adding or removing books, you can notify all the listeners registered to the inventory class every time these actions occur.

假设所有的库存更改都是添加或删除书籍这类动作的结果，那么可以在每次发生这些动作的时候通知所有注册到Inventory类的侦听器。

youdao

Gross domestic investment - GDI: Outlays for additions to the fixed assets of the economy plus the net value of inventory changes.

国内投资总额(简写为GDI)：一个国家增加的固定资产开支，加上存货变动的净值。

youdao

Inventory changes on a daily basis, and Tighe emails his entire network when he receives a new shipment.

FORBES: A Matchmaker for Excess Drugs and the Patients Who Need Them

That makes some of the top line numbers problematic because inventory changes are notoriously hard to interpret correctly.

FORBES: Our Inventory Recovery

Real final sales (real GDP minus inventory changes) were up only 0.9 percent.

FORBES: Our Inventory Recovery