[英]Converting stateful React component to stateless functional component: How to implement "componentDidMount" kind of functionality?
我寫了一個小的有狀態的 React 組件。 當這個組件加載時,在componentDidMount
方法中,我使用 Kendo UI 在彈出窗口中顯示組件的內容。
這是我的代碼:
export class ErrorDialog extends React.Component {
constructor(props, context) {
super(props, context);
this.errorPopupWindow = null;
window.addEventListener('resize', this.resizeComponent);
this.handleWindowKeyDown = this.handleWindowKeyDown.bind(this);
this.handleButtonCloseWindowOnClick = this.handleButtonCloseWindowOnClick.bind(this);
this.handleButtonShowDetailsOnClick = this.handleButtonShowDetailsOnClick.bind(this);
$('#ErrorInformationForm-CloseWindow').focus();
}
render() {
const errorInformation = this.props.errorInformation;
const baseException = errorInformation.baseException;
const showExceptionMessage = (typeof baseException !== 'undefined' && typeof baseException === 'object' && baseException !== null
&& typeof baseException.message !== 'undefined' && typeof baseException.message === 'string' && baseException.message !== null
&& baseException.message !== '') ? true : false;
const baseExceptionMessage = showExceptionMessage ? baseException.message : '';
const exceptionMessageCss = showExceptionMessage ? 'k-textbox ce-width-100-pct ce-margin-top-5' : 'ce-invisible';
return(
<div id="Error-Dialog-Popup" onKeyDown={this.handleWindowKeyDown}>
<div className="ce-window-body">
{errorInformation.message}
<code>
<textarea readOnly={true} className={exceptionMessageCss} rows="3" defaultValue={baseExceptionMessage} />
</code>
</div>
</div>
);
}
componentDidMount() {
const errorInformation = this.props.errorInformation;
const modalWindowTitle = '<span class="ce-width-100-pct ce-app-color-red"><i class="fa ce-fs-1-2-5x fa-times-circle"></i> ' + errorInformation.heading + '</span>';
$('#Error-Dialog-Popup').kendoWindow({
actions: [],
width: 500,
height: 130,
visible: true,
modal: true,
title: modalWindowTitle,
resizable: false
});
this.resizeComponent();
}
resizeComponent() {
}
closeWindowIfPossible(evt) {
}
handleWindowKeyDown(evt) {
}
handleButtonShowDetailsOnClick(evt) {
}
handleButtonCloseWindowOnClick(evt) {
}
}
鑒於此組件不需要維護任何狀態,我正在嘗試將此組件轉換為無狀態功能組件。
我掙扎的地方是如何實現 componentDidMount 功能? 這是我到目前為止編寫的代碼:
export const ErrorDialog = (props, context) => {
const errorInformation = props.errorInformation;
const baseException = errorInformation.baseException;
const showExceptionMessage = (typeof baseException !== 'undefined' && typeof baseException === 'object' && baseException !== null
&& typeof baseException.message !== 'undefined' && typeof baseException.message === 'string' && baseException.message !== null
&& baseException.message !== '') ? true : false;
const baseExceptionMessage = showExceptionMessage ? baseException.message : '';
const exceptionMessageCss = showExceptionMessage ? 'k-textbox ce-width-100-pct ce-margin-top-5' : 'ce-invisible';
const resizeComponent = () => {
}
const closeWindowIfPossible = (evt) => {
}
const handleWindowKeyDown = (evt) => {
}
const handleButtonShowDetailsOnClick = (evt) => {
}
const handleButtonCloseWindowOnClick = (evt) => {
}
const handleComponentOnLoad = (evt) => {
console.log('comes in onLoad');
const errorInformation = props.errorInformation;
const modalWindowTitle = '<span class="ce-width-100-pct ce-app-color-red"><i class="fa ce-fs-1-2-5x fa-times-circle"></i> ' + errorInformation.heading + '</span>';
$('#Error-Dialog-Popup').kendoWindow({
actions: [],
width: 500,
height: 130,
visible: true,
modal: true,
title: modalWindowTitle,
resizable: false
});
resizeComponent();
}
return(
<div id="Error-Dialog-Popup" onLoad={handleComponentOnLoad} onKeyDown={handleWindowKeyDown}>
<div className="ce-window-body">
{errorInformation.message}
<code>
<textarea readOnly={true} className={exceptionMessageCss} rows="3" defaultValue={baseExceptionMessage} />
</code>
</div>
</div>
);
}
起初,我以為我可以在 div 的onLoad
事件處理程序中實現componentDidMount
類型的功能,但是當我嘗試這樣做時,我注意到該事件根本沒有被觸發(然后我閱讀了文檔並發現我真的不能使用此事件:))。
所以我的問題是:
componentDidMount
類型的功能? 本質上,我需要做的是在組件加載到 DOM 時對其進行處理。他們所說的(上面),但也考慮制作一個有狀態的組件容器並將 props/args 傳遞給無狀態的子組件。
在 React 16.8 中,您現在可以對功能組件使用狀態掛鈎。 對於componentDidMount
,建議使用Effect Hooks 。
import React, { useState, useEffect } from 'react';
function Example() {
// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
// Similar to componentDidMount and componentDidUpdate:
useEffect(() => {
document.title = `You clicked ${count} times`;
}, [count]); // Only re-run the effect if count changes)
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
演示: https : //codepen.io/rjruizes/pen/yLMZPvR
如果您希望 Effect Hook 僅在掛載后運行,請使用空數組作為條件:
useEffect(() => {
document.title = `You clicked ${count} times`;
}, []);
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