如何从ReactJs的父组件访问子组件的输入值？

如何解决如何从ReactJs的父组件访问子组件的输入值？

我在访问输入值时遇到问题，我在这里使用的是 .map（）。 这是代码，<QuestionLabel/>是子组件。 projectsData.projectDetail是可用数据

//..
{projectsData.projectDetail.questions.map((question) => (
                    <QuestionLabel
                        questionTitle={question}  
                    />
                ))}


//child component
const QuestionLabel=(props)=>{
    const [answerInput,setAnswerInput] = React.useState("");
     return(
         <div className="contact">
            <form  className="contact-form" autocomplete="off">
                <div class="contact-form-group">
                    <label 
                        for="name" 
                        class="contact-form-label"
                    >
                        {props.questionTitle}
                    </label>
                    <input 
                        id="name" 
                        type="text" 
                        class="contact-form-input"
                        value={answerInput}
                        onChange={(answer) => setAnswerInput(answer.target.value)}

                />
                </div>
                
            </form>
     </div>
     );
 }
 export default QuestionLabel;

解决方法

有很多方法可以从子组件中获取价值以作为父组件。您可以调用从父级到子级的函数传递，以在value设置为parent state时对其进行更改。例子：

const ParentComponent =(props)=>{
    const [valueFromChild,setValueFromChild] = useState('');

    return <>
        {valueFromChild}
        <QuestionLabel questionTitle={'Title'} setValueFromChild={setValueFromChild}/>
        </>
}

const QuestionLabel=(props)=>{
    const [answerInput,setAnswerInput] = React.useState("")

    useEffect(() => {
        props.setValueFromChild(answerInput);
    },[answerInput]);

    return(
        <div className="contact">
            <form  className="contact-form" autoComplete="off">
                <div class="contact-form-group">
                    <label
                        for="name"
                        class="contact-form-label"
                    >
                        {props.questionTitle}
                    </label>
                    <input
                        id="name"
                        type="text"
                        class="contact-form-input"
                        value={answerInput}
                        onChange={(answer) => setAnswerInput(answer.target.value)}
                    />
                </div>

            </form>
        </div>
    );
} 

,

因此，您需要在父级中设置输入状态。

由于您要遍历问题数组以呈现QuestionLabel，所以我们可以尝试...

//..
const ParentComponent = () => {
  const [answers,setAnswers] = React.useState({})

  useEffect(() => {
    projectsData.projectDetail.questions.forEach((_,i) => {
      setAnswers(previousAnswers => {...previousAnswers,["name" + i]: ""})
    })
  },[])

  const handleAnswers = (e) => {
    setAnswers(previousAnswers => {...previousAnswers,[e.target.name]: [e.target.value]})
  }
//..

然后

//..
{
  projectsData.projectDetail.questions.map((question,i) => {
    return (
      <QuestionLabel questionTitle={question} inputName={"name" + i} answers={answers} handleAnswers={handleAnswers} />
    )
  })
}

最后...

//child component
const QuestionLabel=(props)=>{

     return(
         <div className="contact">
            <form  className="contact-form" autocomplete="off">
                <div class="contact-form-group">
                    <label 
                        for={props.inputName}
                        class="contact-form-label"
                    >
                        {props.questionTitle}
                    </label>
                    <input 
                        id={props.inputName}
                        name={props.inputName} 
                        type="text" 
                        class="contact-form-input"
                        value={answers[props.inputName]}
                        onChange={handleAnswers}
                />
                </div>
                
            </form>
     </div>
     );
 }
 export default QuestionLabel;