rerender react component when prop changes

问题:

I'm trying to separate a presentational component from a container component. I have a SitesTable and a SitesTableContainer. The container is responsible for triggering redux actions to fetch the appropriate sites based on the current user. The problem is the current user is fetched asynchronously, after the container component gets rendered initially. This means that the container component doesn't know that it needs to re-execute the code in its componentDidMount function which would update the data to send to the SitesTable. I think i need to rerender the container component when one one of its props(user) changes. How do i do this correctly?

class SitesTableContainer extends React.Component {
    static get propTypes() {
      return {
        sites: React.PropTypes.object,
        user: React.PropTypes.object,
        isManager: React.PropTypes.boolean
      }
     }

    componentDidMount() {
      if (this.props.isManager) {
        this.props.dispatch(actions.fetchAllSites())
      } else {
        const currentUserId = this.props.user.get('id')
        this.props.dispatch(actions.fetchUsersSites(currentUserId))
      }  
    }

    render() {
      return <SitesTable sites={this.props.sites}/>
    }
}

function mapStateToProps(state) {
  const user = userUtils.getCurrentUser(state)

  return {
    sites: state.get('sites'),
    user,
    isManager: userUtils.isManager(user)
  }
}

export default connect(mapStateToProps)(SitesTableContainer);

回答1:

You have to add a condition in your componentWillReceiveProps method.

This is how your component should look like

constructor(){
  this.updateUser = this.updateUser.bind(this);
}  


componentDidMount() {
  this.updateUser();

}

componentWillReceiveProps(nextProps) {
    if(JSON.stringify(this.props.user) !== JSON.stringify(nextProps.user)) // Check if it's a new user, you can also use some unique property, like the ID
    {
           this.updateUser();
    }
} 

updateUser() {
  if (this.props.isManager) {
    this.props.dispatch(actions.fetchAllSites())
  } else {
    const currentUserId = this.props.user.get('id')
    this.props.dispatch(actions.fetchUsersSites(currentUserId))
  }  
}

UPDATE (React 17)

Looks like componentWillReceiveProps is going to be removed in React 17. You can use componentDidUpdate instead of componentWillReceiveProps to achieve the same thing.

The new example is using fast-deep-equal instead of JSON.stringify() to compare the objects.

import equal from 'fast-deep-equal'

...

constructor(){
  this.updateUser = this.updateUser.bind(this);
}  


componentDidMount() {
  this.updateUser();

}

componentDidUpdate(prevProps) {
    if(!equal(this.props.user, prevProps.user)) // Check if it's a new user, you can also use some unique property, like the ID  (this.props.user.id !== prevProps.user.id)
    {
           this.updateUser();
    }
} 

updateUser() {
  if (this.props.isManager) {
    this.props.dispatch(actions.fetchAllSites())
  } else {
    const currentUserId = this.props.user.get('id')
    this.props.dispatch(actions.fetchUsersSites(currentUserId))
  }  
}

回答2:

ComponentWillReceiveProps() is going to be deprecated in the future due to bugs and inconsistencies. An alternative solution for re-rendering a component on props change is to use ComponentDidUpdate() and ShouldComponentUpdate().

ComponentDidUpdate() is called whenever the component updates AND if ShouldComponentUpdate() returns true (If ShouldComponentUpdate() is not defined it returns true by default).

shouldComponentUpdate(nextProps){
    return nextProps.changedProp !== this.state.changedProp;
}

componentDidUpdate(props){
    // Desired operations: ex setting state
}

This same behavior can be accomplished using only the ComponentDidUpdate() method by including the conditional statement inside of it.

componentDidUpdate(prevProps){
    if(prevProps.changedProp !== this.props.changedProp){
        this.setState({          
            changedProp: this.props.changedProp
        });
    }
}

If one attempts to set the state without a conditional or without defining ShouldComponentUpdate() the the component will infinitely re-render

回答3:

componentWillReceiveProps(nextProps) { // your code here}

I think that is the event you need. componentWillReceiveProps triggers whenever your component receive something through props. From there you can have your checking then do whatever you want to do.

回答4:

I would recommend having a look at this answer of mine, and see if it is relevant to what you are doing. If I understand your real problem, it's that your just not using your async action correctly and updating the redux "store", which will automatically update your component with it's new props.

This section of your code:

componentDidMount() {
      if (this.props.isManager) {
        this.props.dispatch(actions.fetchAllSites())
      } else {
        const currentUserId = this.props.user.get('id')
        this.props.dispatch(actions.fetchUsersSites(currentUserId))
      }  
    }

Should not be triggering in a component, it should be handled after executing your first request.

Have a look at this example from redux-thunk:

function makeASandwichWithSecretSauce(forPerson) {

  // Invert control!
  // Return a function that accepts `dispatch` so we can dispatch later.
  // Thunk middleware knows how to turn thunk async actions into actions.

  return function (dispatch) {
    return fetchSecretSauce().then(
      sauce => dispatch(makeASandwich(forPerson, sauce)),
      error => dispatch(apologize('The Sandwich Shop', forPerson, error))
    );
  };
}

You don't necessarily have to use redux-thunk, but it will help you reason about scenarios like this and write code to match.