当我使用 setstate 调用 function 时，State 值不会改变

Question

addTOList= (id) =>{
  const movieId = id
  const movie = movies.find( ({ id }) => id === movieId );
  const stateMovie = [...this.state.movie, movie]
  console.log(stateMovie)
  this.setState({
    movie : stateMovie
  })
  console.log(this.state.movie)
  localStorage.setItem('movies', JSON.stringify(this.state.movie))
  this.state.movie.map(mov =>{
  })
}

This function will be triggered when the (Add to list) button is clicked. but I have to click twice to change the state.` sorry for horrible English

Answer 1

react state changes are synchronous.

Check this question & answer here

Answer 2

If your 'next state' depends on the 'previous state' then you should use this pattern:

  this.setState(prev => ({
    ...prev,
    movie : [...prev.movie, movie],
  }))

Also you must wait until the state change has been applied by react before you will see the changes in your console statement.

Answer 3

setState is an async function, it do not setstate in async manner but later, you can use a callback function, if you want to run a code snippet after set state is run:

addTOList = () => { this.setState({ movie: stateMovie }, () => { console.log(this.state.movie) }) }

Answer 4

again myself, I did some change and this worked but I no Idea this is the right way to do or not

addTOList= (id) =>{
const movieId = id
const movie = movies.find( ({ id }) => id === movieId );
const stateMovie = [...this.state.movie, movie]
console.log(stateMovie)
this.state.movie = stateMovie
this.setState({})

console.log(this.state.movie)
localStorage.setItem('movies', JSON.stringify(this.state.movie))
this.state.movie.map(mov =>{
})

}