How to set state of parent component from a child component in react?

Question

I have a state in Parent Component that has an Array of patients. My Child Component 4 is a Countdown component (// countdown component renders individually countdown for each patient in the array) and when the countdown gets to <=0, I would like to reset the patient’s locationInfo & status value to be empty string in the patient array. In my parent component, I have resetPatient function that maps over the patient array and should set the values(locationInfo & status) of the patient that has <=0 counter to empty strings. The resetPatient function is passed as props down to my Countdown component(4). In Countdown component I call the this.props.resetPatient function when the counter gets to <=0. However, this is not working for me. The state on Parent Component doesn’t change.

Parent Component - Child Component 1 - Child Component 2 - Child Component 3 - Child Component 4

Parent component 

export default class ObservationWorkflow extends React.Component {


    constructor(props) {
        super(props);
       this.state = {

         patients = [
           { room: "1", name: 'John', locationInfo: 'TV', status: 'Awake'},
           { room: "2", name: 'Shawn, locationInfo: 'Toilet', status: 'Awake'},
           { room: "3", name: 'Gereth, locationInfo: 'Garden', status: 'Awake'}
          ]
         }
       this.resetPatient = this.resetPatient.bind(this);

 }


    resetPatient = (patient, index) => {

        this.setState(prevState => ({

            patients: prevState.patients.map((patient, i) => {
                if (i === index) {
                    return {
                        ...patient,
                        locationInfo: '', 
                        status: ''
                    };
                }
                return patient;
            }),
        }));
    }

   render() {
      return (
    <Child component(1)={this.resetPatient} // then child component 2 passes it down as props to 3 then 4. 
     )
   }
}

Countdown component(4)// countdown component renders individually countdown for each patient in the array. 

 export default class ObservationCountDown extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            obsTimeleft: undefined
        };

        this.countDown = this.countDown.bind(this);
        this.startCountdown = this.startCountdown.bind(this);
        this.countDownInterval = null;
    }

    countDown() {

        const { obsTakenTime, patient, index } = this.props; 
        const nextDueTimeForObs = moment(obsTakenTime).add(10, 'minutes'); 

        const nextObservationTime = nextDueTimeForObs.subtract(moment.now()).format('mm');

        if (obsTakenTime) {
            this.setState({ obsTimeleft: nextObservationTime + ' mins' });
        }
        if (Number(nextObservationTime) <= 1) {
            this.props.disablePatientUpdate();
        }
        if (Number(nextObservationTime) <= 0) {
            this.setState({ obsTimeleft: 'Overdue' });
            this.props.enablePatientUpdate();
            clearInterval(this.countDownInterval);

            () => this.props.resetPatient(patient, index); // here i call the function as call back
        }
    }

How to set the state of parent component from a child component in react.

Answer 1

It looks like you're not calling resetPatient, and that index isn't defined in that scope in any case.

I would add an id to your patient object and use this to identify which one needs to be reset:

 patients = [
       { id:1, room: "1", name: 'John', locationInfo: 'TV', status: 'Awake'},
       { id:2, room: "2", name: 'Shawn, locationInfo: 'Toilet', status: 'Awake'},
       { id:3, room: ... }]

and your resetPatient would become:

 resetPatient = (patient) => {

    this.setState(prevState => ({

        patients: prevState.patients.map(p => {
            if (patient.id === p.id) {
                return {
                    ...p,
                    locationInfo: '', 
                    status: ''
                };
            }
            return p;
        }),
    }));
}

Then you can just call:

   this.props.resetPatient(patient)