state 在 shouldComponentUpdate 之后和渲染之前是否得到更新

Question

I'm new to React, just a question on how component's state object get updated. After analyzing some code, I think:

In update phase, state get updated after shouldComponentUpdate method but before render method, is my understanding correct?

If the answer is yes, is it another dedicated method(sth like "UpdatingState") to updated the state object?

Answer 1

updating state in react is done through the setState lifecycle method

you can call it like this this.setState({name: 'new name'}) this updates the state object key name to be the new value, in this case new name

updating objects is a little bit harder. you have to first clone the object. then change the value then reset the state like so

state = {
   person: {
     name: 'peter',
     age: 25
}

const copy = {...this.state.person}
copy.name = 'new name'
this.setState({copy})

Answer 2

Yes, the state will be updated ( setState ) after shouldComponentUpdate. The order of update phase would be

1. getDerivedStateFromProps
2. shouldComponentUpdate
3. render
4. componentDidUpdate

to update state use setState

Answer 3

there is a function that is called after each update in state and props:

componentDidUpdate(prevProps , prevState)