如何将异步状态传递给子组件prop? [英] How to pass async state to child component props?

问题描述

我是新手，我正在尝试从API提取数据并将数据传递给子组件.我已经将数据传递给父组件的状态，但是当我将其作为道具传递给子组件时，它会记录为一个空数组.我确定有一些简单的事情我可以忽略，但是我不知道是什么，我的代码在下面

I'm new to react and I am trying to fetch data from an API and pass the data to a child component. I've passed the data to the state on my parent component, however, when I pass it to the child component as props it logs as an empty array. I'm sure there is something simple I am overlooking but I don't know what, my code is below

父项

import React, {Component} from 'react';
import Child from '../src/child';
import './App.css';

class App extends Component {
    constructor(props) {
        super(props);

        this.state = {
          properties: []
        }
    }

    getData = () => {
        fetch('url')
        .then(response => {
            return response.text()
        })
        .then(xml => {
            return new DOMParser().parseFromString(xml, "application/xml")
        })
        .then(data => {
            const propList = data.getElementsByTagName("propertyname");
            const latitude = data.getElementsByTagName("latitude");
            const longitude = data.getElementsByTagName("longitude");

            var allProps = [];

            for (let i=0; i<propList.length; i++) { 
                allProps.push({
                    name: propList[i].textContent,
                    lat: parseFloat(latitude[i].textContent), 
                    lng: parseFloat(longitude[i].textContent)
                });
            }

            this.setState({properties: allProps});
        });
    }

    componentDidMount = () => this.getData();

    render () {
        return (
            <div>
                <Child data={this.state.properties} />
            </div>
        )
    }
}

export default App;

儿童组件

import React, {Component} from 'react';

class Child extends Component {
    initChild = () => {
        console.log(this.props.data); // returns empty array

        const properties = this.props.data.map(property => [property.name, property.lat, property.lng]);
    }

    componentDidMount = () => this.initChild();

    render () {
        return (
            <div>Test</div>
        )
    }
}

export default Child;

推荐答案

将子级中的componentDidMount更改为componentDidUpdate.

Change the componentDidMount in the child to componentDidUpdate.

componentDidMount生命周期方法在开始时仅被调用一次.而只要应用程序状态发生变化，就会调用componentDidUpdate生命周期方法.由于api调用是异步的，因此在将api调用的结果传递给子级之前，initChild()函数已经被调用一次.

The componentDidMount lifecycle method is called only once in the starting. Whereas, the componentDidUpdate lifecycle method gets called whenever there is a change in the state of the application. Since api calls are asynchronous, the initChild() function is already called once before the api call's results are passed to the child.

这篇关于如何将异步状态传递给子组件prop?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！