基础
示例工程：formik-09x-component-lifecycle-events-example
核心文件：index.js
示例说明
Formik大部分示例工程中都使用了极其方式创建Formik表单组件，本示例中则使用了复杂（或者说典型）方式创建一个Formik表单组件，即使用其继承自React.Component组件，从而展示有关生命周期事件的基本使用。但是，也比较简单，只涉及到了两个事件：
-
componentwillReceiveProps
-
render
但是，这个示例中使用的componentwillReceiveProps事件在最新的React中已经过时。引用一个老外的话说是：
This lifecycle,however,is on the deprecation path; it will stop working as-named in React 17: https://reactjs.org/docs/react-component.html#unsafe_componentwillreceiveprops
Given that,we should provide a more future-friendly solution for listening for shallow route changes. Perhaps adding a popstate listener in componentDidMount. If that seems like the best option I can add it to docs,but opening this ticket for discussion/tracking.
现在，在最新版本React环境下需要使用UNSAFE_componentwillReceiveProps()来代替。
另外：在新版本中，官方明确指出使用上述事件容易导致一些复杂BUG的出现，所以官方建议使用事件来代替。另外，还有如下建议：
Note:
Using this lifecycle method often leads to bugs and inconsistencies,and for that reason it is going to be deprecated in the future.
If you need to perform a side effect (for example,data fetching or an animation) in response to a change in props,use componentDidUpdate lifecycle instead.
For other use cases,follow the recommendations in this blog post about derived state.
If you used componentwillReceiveProps for re-computing some data only when a prop changes,use a memoization helper instead.
If you used componentwillReceiveProps to “reset” some state when a prop changes,consider either making a component fully controlled or fully uncontrolled with a key instead.
In very rare cases,you might want to use the getDerivedStateFromProps lifecycle as a last resort.
引用
1，https://github.com/zeit/next.js/issues/4154
2，https://reactjs.org/docs/react-component.html#unsafe_componentwillreceiveprops
