Question

继续这个问题 - Javascript - How do I access properties of objects nested within other Objects

标准点表示法似乎不适用于访问React state / props

中的嵌套对象属性

下面给出了道具：如何检索纬度？

Object {
id: "138451",
name: "Attendant",
 key: "Taiwan", 
defaultAnimation: 2, 
position: Object
 {
latitude:0.5,
longitude: -0.14
}
componentWillReceiveProps(nextProps){
  console.log("its getting props");
  console.log(nextProps.markers[0]) // this works
//displays Object {position: Object, key: 2, defaultAnimation: 2}
      console.log(nextProps.markers[0].position) //so does this
//displays Object {latitude: 51.5193, longitude: -0.140725}
      console.log(nextProps.markers[0].position.longitude) //breaks with the error message

TypeError: Cannot read property 'longitude' of undefined
    at GooleMapComponent.componentWillReceiveProps (http://localhost:3000/app/app.js?....

Answer 1

以下是如何使用点表示法在Child的componentWillReceiveProps方法以及render()方法中访问React props中的嵌套对象属性的演示：http://codepen.io/PiotrBerebecki/pen/qaKyYj

class App extends React.Component {
  constructor() {
    super();
    this.handleClick = this.handleClick.bind(this);
    this.state = {
      markers: null
    }
  }

  handleClick() {
    this.setState({
      markers: [
        { 
          id: "138451",
          name: "Attendant",
          key: "Taiwan", 
          defaultAnimation: 2, 
          position: {
            latitude: 0.5,
            longitude: (-Math.random()).toFixed(2)
          }
        }
      ]
    });
  }  

  render() {
    return (
      <div>
        <h1>App</h1>
        <button onClick={this.handleClick}>Send State via Props</button>
        <Child markers={this.state.markers}/>     
      </div>
    );
  }
}

class Child extends React.Component {
  componentWillReceiveProps(nextProps) {
    console.clear();
    console.log('in componentWillReceiveProps', nextProps.markers[0]);
    console.log('in componentWillReceiveProps', nextProps.markers[0].position);
    console.log('in componentWillReceiveProps', nextProps.markers[0].position.longitude);
  }

  render() {
    if (this.props.markers) {
      return (
       <div>
          <h5>Child happy :) child received an array via props</h5>
          Longitute: {this.props.markers[0].position.longitude}
       </div>
      );
    } else {
      return (
       <div>
          <h5>Child not happy :( Child received 'null' via props</h5>
       </div>
     );
    }
  }
}

ReactDOM.render(
  <App />,
  document.getElementById('app')
);

如何在React props中访问嵌套对象属性

1 个答案: