The system event for changing or updating a view is almost always (dare I say always?) a request from the user.

用于更改或更新视图的系统事件几乎总是(为什么我敢说总是呢？)用户请求。

youdao

This example solves a common problem: how do you attach changing behavior to a user interface event?

这个例子解决了一个常见问题：如何将更改中的行为附加到用户接口事件？

youdao