从父组件更新子组件的状态

Question

假设我的父组件有两个子组件：

Parent
| Child1
| Child2

我从 Child2 获得输入并将其传递给 Parent 组件（直到现在，我知道该怎么做）。但是我需要将该输入传递给 Child1 以更新它的状态。

我该怎么做？

Answer 1

**组件父级**

   import React from 'react';
    import MM from './modall';
    class App extends React.Component {
        constructor() {
            super();
            this.state = {
                naslov:'',
                telo:''
            };
            this.setStateHandler = this.setStateHandler.bind(this);
            this.postaviStanje = this.postaviStanje.bind(this);
            this.Stanje = this.Stanje.bind(this);
        }
        setStateHandler() {
            this.setState({ naslov: "Naslov Prvi u Modalu", telo:"Novo Prvo telo modala"});

        };
        postaviStanje(){
          this.setState({naslov: " Novi drugi u Modalu", telo:"Novo drugo  telo modala"});
        };
        Stanje(){
          this.setState({naslov: " Novi treci u Modalu", telo:"Novo trece  telo modala"});

        };
        render() {
            return (
                <div>
                    <button onClick = {this.setStateHandler} data-toggle="modal" data-target="#modal">SET STATE</button>
                    <button onClick = {this.postaviStanje} data-toggle="modal" data-target="#modal">SET STATE2</button>
                    <button onClick = {this.Stanje} data-toggle="modal" data-target="#modal">SET STATE3</button>
                    <MM telo={this.state.telo} naslov={this.state.naslov} />)

                </div>
            );
        }
    }
    export default App;

子项

 /**
     * Created by trika on 31-Jan-18.
     */
    import React,{Component} from 'react';

    class Modal extends Component{
        constructor(props) {
            super(props);
            this.state = {
                naslov:this.props.naslov,
                telo: this.props.telo
            };
        }

        render(){

            return(
                <div className="modal" id="modal" role="dialog">
                    <div className="modal-dialog" role="document">
                        <div className="modal-content">
                            <div className="modal-header">
                                <h1 className="modal-title"><strong>{this.props.naslov}</strong></h1>
                                <button type="button" className="close" data-dismiss="modal" aria-label="Close">
                                    <span aria-hidden="true">&times;</span>
                                </button>
                            </div>
                            <div className="modal-body">
                                <p>Modal body text goes here.</p>
                                <h2><strong>{this.props.telo}</strong></h2>
                            </div>
                            <div className="modal-footer">
                                <button type="button" className="btn btn-primary">Save changes</button>
                                <button type="button" className="btn btn-secondary" data-dismiss="modal">Close</button>
                            </div>
                        </div>
                    </div>
                </div>
            );
        }
    }

    export default Modal;

Answer 2

希望您能理解主要思想 - 在 Parent 组件中创建一个函数，该函数将更改传递给 Child1 的值。 ReactJS: Why is passing the component initial state a prop an anti-pattern?

class Parent extends Component {
  constructor(props){
    super(props);
    this.state = {
      value: ""
    }
  }
  changeValue(value){
    this.setState({value});
  }
  render(){
    return (
      <div>
          <Child1 value={this.state.value}/>
          <Child2 changeValue={changeValue}/>
      </div>
    )
  }
}


class Child2 extends Component {
  constructor(props) {
    super(props);
    this.state={
      input: ""
    }
  }
  handleChange(e){
    var {value} = e.target;
    this.setState({
      input: value
    },() => this.props.changeValue(value));
  }
  render(){
    return (
      <div>
          <input value={this.state.input} onChange={this.handleChange}/>
      </div>
    )
  }
}



class Child1 extends Component {

  constructor(props) {
    super(props);
    this.state={value:''}
  }
  componentWillReceiveProps(nextProps) {
    this.setState({value: nextProps.value})
  }


  render(){
    return (
      <div>
          {this.props.value}
      </div>
    )
  }
}

Answer 3

您可以在子组件中拥有一个函数，该函数根据父组件发送的值更新状态。您可以使用refs访问父组件的子组件的功能

例子

家长：

class Parent extends React.Component {
     funcUpdateChild1 = () => {
          this.child1.updateState('value here');
     }
     render() {
          return (
              <Child1 ref={(ip) => {this.child1 = ip}} />
              <Child2 ref={(ip) => {this.child2 = ip}} />
         ) 
     }
}

孩子1

class Child1 extends React.Component {
     updateState = (value) => {
         //use the value to set state here
     }
     render() {
          return (
              //child1 contents here
         ) 
     }
}