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[英]Why is a Component Re-Rendering done when changing the value of the props sent to child Component (react js)?
[英]Why is my react component not re rendering when props comes into the component?
我目前正在一個項目中,我必須對通過redux或將其傳遞給自己的子組件中的每個道具進行空檢查。 我覺得這不正常嗎? React的巨大優勢不是自動重新渲染嗎? 如果我嘗試將任何東西置於狀態,那么我就不能這樣做,因為在對數據進行任何處理之前,必須在渲染中進行null檢查。 提前致謝!!
父組件=
class App extends Component {
componentDidMount(){
//where I load the data
this.loadCardsFromServer();
this.props.GetAllData();
}
render() {
//NEED TO DO A NULL CHECK FROM THIS COMING FROM REDUX
const filteredData = !!this.state.data ? this.state.data.filter(card =>{
return card.name.toUpperCase().includes(this.state.input.toUpperCase())
}) : null;
return (
//MAKES ME DO ANOTHER NULL CHECK
<div>
{!!this.state.data ? filteredData.map(i => <Card person={i} key={i.created} planet={this.props.planets} />) : null}
</div>
))}
兒童卡片
class Card extends Component {
//WHERE I WANT TO PUT THE PROPS
constructor(){
super();
this.state={
edit: false,
name: this.props.person.name,
birthYear: this.props.person.birth_year
}
}
render() {
let world = null;
//ANOTHER NULL CHECK
if(this.props.planet){
this.props.planet.map(i => {
if(i.id === this.props.person.id){
world = i.name
}
})
}
return (
<div>
//THIS IS WHERE I WANT THE VALUE TO BE STATE
{this.state.edit ? <input label="Name" value={this.state.name}/> : <div className='card-name'>{name}</div>}
</div>
您需要在數據到達時更新狀態。 您可以這樣做:
import React, { Component } from 'react';
import './App.scss';
import Card from './Components/Card/Card.js';
class App extends Component {
constructor(){
super();
this.state = {
loading:true,
cards:[]
};
}
componentDidMount(){
this.loadCardsFromServer();
}
loadCardsFromServer = () => {
let cardsResponseArray = [];
// fetch your cards here, and when you get data:
// cardsResponseArray = filterFunction(response); // make function to filter
cardsResponseArray = [{id:1,name:'aaa'},{id:2,name:'bbb'}];
setTimeout(function () {
this.setState({
loading:false,
cards: cardsResponseArray
});
}.bind(this), 2000)
};
render() {
if(this.state.loading === true){
return(
<h1>loading !!!!!!!!</h1>
);
} else {
return (
<div>
{this.state.cards.map(card => (
<Card key={card.id} card={card}></Card>
))}
</div>
);
}
}
}
export default App;
然后在您的Card組件中:
import React, { Component } from 'react';
class Card extends Component {
constructor(props){
super(props);
this.props = props;
this.state = {
id:this.props.card.id,
name:this.props.card.name
};
}
render() {
return (
<div className={'class'} >
Card Id = {this.state.id}, Card name = {this.state.name}
</div>
);
}
}
export default Card;
對於那些對React狀態和生命周期方法感興趣的人, 請點擊此處
好的,在這種情況下,我在redux商店中為等待狀態創建了一個小助手。 我在某處(應用程序)獲取數據,並渲染一個連接的組件,等待存儲中獲取的數據:
const Loader = (props) => {
if (!props.loaded) {
return null;
}
<Card data={props.data}/>
}
const CardLoader = connect (state => {
return {
loaded: state.data !== undefined
data: state.data
}
})(Loader)
<CardLoader />
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