How to access child state in react?

Question

I have made my own form component with render() method looks like this:

 render() {
    return (
        <form onSubmit={this.onSubmit} ref={(c)=>this._form=c}>
            {this.props.children}
        </form>
    )
}

Notice that children are rendered here as {this.props.children}, so the user can use this component like this:

 <Form onSubmit={this.submit}   >
            <Input  name={"name"} id="name"  labelName="Ime" placeholder="Unesite ime" type="text" >
                 <Validation rule="required" message="Ovo je obavezno polje"/>
            </Input>
            <Input  name={"email"} id="email"  labelName="Email" placeholder="Unesite email adresu" type="text" >
                <Validation rule="required" message="Ovo je obavezno polje"/>
                <Validation rule="email" message="Ovo je nije valjana email adresa"/>
            </Input>
            <button type="submit" value="Pošalji" >Pošalji</button>
       </Form>

I would like to check the state of each Input component (to get its validity) inside onSubmitMethod().

  checkValidity() {
    var sefl = this;
    this.props.children.map((child) => {
        if (child.type.name === "Input") {

//How to get state of child here
        }
    });
}
onSubmit(event) {
    event.preventDefault();
    var obj = serialize(this._form, { hash: true });
    const validityOfForm = true; //hardcoded for now
    this.checkValidity();
    this.props.onSubmit(obj, validityOfForm);

}

score 4 · Accepted Answer · edited May 23 '17 at 12:03

I have done similar thing in a project by passing state of parent as a prop in child to access child component data in parent component for form elements.

In your case if you send component's state in its child as a prop and each child use state of parent like this.props.state.variablename and not this.state.variablename. You will have control on child components' states / data.

Sending state to childrens from form component using this.prop.children as a prop is not straight forward. Below link helps in doing this.

https://stackoverflow.com/a/32371612/1708333

Example:

Parent component:

<FormFields
    state={this.state}
    _onChange={this._onChange}
/>

Child component

<Input
    name="fieldname"
    value={this.props.state.fieldname}
    type="text"
    label="Lable text"
    validationMessage={this.props.state.validationMessages.fieldname} 
    onChange={this.props._onChange}
/>

Let me know if you need more information.

score 2 · Answer 2 · edited May 23 '17 at 11:47

2

Put a ref, say myinput, to the child and get its state by this.refs.myinput.state to access the child's state if you have to.

However, take a look at this thread before you put the ref. There is a better pattern.

edited May 23 '17 at 11:47

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answered Oct 21 '16 at 10:25

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Yes, but input ref is not ref of a Form component, so when I say this.refs inside Form component I get undefined – Vlado Pandžić Oct 21 '16 at 10:27
1

Other problem I have now is thats this.refs.myinput.state only returns state that was defined first time (inside conctructor) not up to date state. – Vlado Pandžić Oct 21 '16 at 11:11

score 0 · Answer 3 · answered Oct 21 '16 at 11:00

Input should have ref defined. That is easy. But because Inputs are defined inside Form's parent component (altought rendered inside Form component (because of {this.props.children}) I should access Form component's parent using child_owner._instance . Relevant part of code is now:

   checkValidity() {
    var sefl = this;
    var errorsCount = 0;
    this.props.children.map((child) => {

        if (child.type.name === "Input") {
            var refs = child._owner._instance.refs;
            var rules = refs[child.ref].state.validationRules;
            var hiddenRules = refs[child.ref].state.validationRulesHidden;
            if (_.filter(_.values(rules), (elem) => elem == true).length > 0 || _.filter(_.values(hiddenRules), (elem) => elem == true).length>0) {
                errorsCount++;
            }
      }

    });
    if (errorsCount == 0) {
        return true;
    }
    return false;
}

There is an [API](https://facebook.github.io/react/docs/react-api.html#react.children.map) to map React children, FYI. — Season, Oct 23 '16 at 02:06

How to access child state in react?

3 Answers3