Map properties to state in react-redux

问题:

I have a component that uses state to provide data to user. For example <div>this.state.variableInState</div>. This component can dispatch some method (for example on onClick action). I'm currently using react-redux an connect method to map store to props. Is there a way I can setState after dispatch?

// actions
export function executeAction() {
  return function (dispatch, getState) {
    dispatch({
      type: 'MY_ACTION',
      payload: axios.get('/some/url')
    });
  };
}
// reducer

export default function (state = {}, action) {
  switch (action.type) {
    case 'MY_ACTION_FULFILLED':
      return {...state, myVariable: action.payload.data}
  }
}
//component
class MyComponent extends Component {
  render() {
    (<div onClick={this.props.executeAction.bind(this)}>
      {this.state.variableInState}
      </div>)
  }

  someOtherMethod() {
    // I want to operate with state here, not with props
    // that's why my div gets state from this.state instead of this.props
    this.setState({variableInState: 'someValue'})
  }
}


export default connect((state, ownProperties) => {
  return {
    // So I want to change MyComponent.state.variableInState here
    // but this method updates MyComponent props only
    // What can I do?
    variableInProps: state.myVariable
  }
}, {executeAction})(MyComponent);

回答1:

Whatever i understand, all you want to do is to convert the component's props to component's own state. You can always change the component's props to component's state in the componentWillReceiveProps life cycle method in component like this.

//component
class MyComponent extends Component {
  componentWillReceiveProps(newProps){
     if(newProps.variableInProps != this.props.variableInProps){
         this.setState({variableInState: newProps.variableInProps })
     }
  }
  render() {
    (<div onClick={this.props.executeAction.bind(this)}>
      {this.state.variableInState}
      </div>)
  }

  someOtherMethod() {
    // I want to operate with state here, not with props
    // that's why my div gets state from this.state instead of this.props
    this.setState({variableInState: 'someValue'})
  }
}


export default connect((state, ownProperties) => {
  return {
    // So I want to change MyComponent.state.variableInState here
    // but this method updates MyComponent props only
    // What can I do?
    variableInProps: state.myVariable
  }
}, {executeAction})(MyComponent);

componentWillReceiveProps method is always executed by react whenever a new props is coming to component so this is the right place to update your component's state according to your props.

UPDATE :

The componentWillReceiveProps has been deprecated. So instead of this method you can use componentDidUpdate method to do this. componentDidUpdate method takes previous props and previous state as arguments. So you can check for the change in props and then set the state.

componentDidUpdate(prevProps) {
  if(prevProps.variableInProps !== this.props.variableInProps){
    this.setState({variableInState: this.props.variableInProps })
  }
}

回答2:

I think you're not supposed to directly change the state like this. why not call another action to perform what you want?

The state should be immutable when using Redux. You should dispatch an action. A Reducer should receive the action and the current state, and return a new state object that includes the changes you want to make. Check this: http://redux.js.org/docs/introduction/ThreePrinciples.html#changes-are-made-with-pure-functions

回答3:

Sure you can, onClick bind to some function like so:

onClick={this.myfunction.bind(this)}

Then define this myfuntion to be:

myfunction() {
    this.setState({ somestate: value });
    this.props.executeAction();
}

Here setState changes native component state, and calling action will change redux state if so defined by reducer. These states are independent.

Connect wrapper (first argument) maps state to props (redux state to react props) not component state itself.

Good question is why you need both, sure there are some examples where this could be useful...

In general if you need state that is needed globally then use redux state (easily applied to all components) and for some local states use react native state. (For example when you build some ui components like custom checkbox)

回答4:

There's also static getDerivedStateFromProps:

static getDerivedStateFromProp(nextProps, prevState) {
  return {stateVar: nextProps.var} // this will propagate as component state
}