setState不更新状态

Question

why this.setState does not work.

constructor(props) {
 super(props);
 this.state ={
    obj: [],
 }
 }
 ,


componentDidUpdate(prevProps){
const { obj } = this.props;
  this.setState({obj});
}
}

Answer 1

If you look at your dev console you'll see an error when that console log is supposed to occur, because you're using a "normal" function without any kind of this preservation. Instead, once that function gets called the this identifier will be referencing the global context (eg window ), rather than your component.

Use an arrow function to make sure this is the one you actually meant, and you'll see that setState worked just fine:

componentDidUpdate(prevProps){
  this.setState({
    siteDataState: this.props.siteData
  }, () => {
    console.log(this.state.siteDataState);
  });
}

That said, this is going to cascade-trigger because you're changing the component in the function that triggers when the component changes , so put some if code in there that makes sure that this.state.siteDataState isn't already what's in this.props.siteData .