Render Props
一種在 React 組件之間使用一個值爲函數的prop, 在React 組件間共享代碼的簡單技術
class MouseTracker extends React.Component {
constructor(props) {
super(props);
this.handleMouseMove = this.handleMouseMove.bind(this);
this.state = { x: 0, y: 0 };
}
handleMouseMove(event) {
this.setState({
x: event.clientX,
y: event.clientY
});
}
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
<h1>Move the mouse around!</h1>
<p>The current mouse position is ({this.state.x}, {this.state.y})</p>
</div>
);
}
}
隨着鼠標在屏幕上移動,在一個 p 標籤的組件上顯示它的 (x, y) 座標。
假設我們現在有一個在屏幕上跟隨鼠標渲染一張貓的圖片的 <Cat>
組件。我們可能使用 <Cat mouse={{ x, y }} prop
來告訴組件鼠標的座標以讓它知道圖片應該在屏幕哪個位置。
首先,你可能會像這樣,嘗試在 的內部的渲染方法渲染 組件:
class Cat extends React.Component {
render() {
const mouse = this.props.mouse
return (
<img src="/cat.jpg" style={{ position: 'absolute', left: mouse.x, top: mouse.y }} />
);
}
}
class MouseWithCat extends React.Component {
constructor(props) {
super(props);
this.handleMouseMove = this.handleMouseMove.bind(this);
this.state = { x: 0, y: 0 };
}
handleMouseMove(event) {
this.setState({
x: event.clientX,
y: event.clientY
});
}
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
<Cat mouse={this.state} />
</div>
);
}
}
這一方法對我們的具體用例來說能夠生效,但我們卻沒法實現真正的將行爲封裝成可重用的方式的目標。現在,每次我們在不同的用例中想要使用鼠標的位置,我們就不得不創建一個新的針對那一用例渲染不同內容的組件 (如另一個關鍵的 <MouseWithCat>
)。
HOC 高階組件實現
class Cat extends React.Component {
render() {
const mouse = this.props.mouse
return (
<img src="https://ss3.baidu.com/-rVXeDTa2gU2pMbgoY3K/it/u=550398634,1506778242&fm=202" style={{ position: 'absolute', left: mouse.x, top: mouse.y }} />
);
}
}
function withMouse(Component) {
return class extends React.Component {
constructor(props) {
super(props);
this.handleMouseMove = this.handleMouseMove.bind(this);
this.state = { x: 0, y: 0 };
}
handleMouseMove(event) {
this.setState({
x: event.clientX,
y: event.clientY
});
}
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
<Component mouse={this.state} />
</div>
)
}
}
}
export default withMouse(Cat);
render prop 實現
我們可以提供一個帶有函數 prop 的<Mouse>
組件,它能夠動態決定什麼需要渲染的,而不是將 硬編碼到 <Mouse>
組件裏,並有效地改變它的渲染結果。
class Cat extends React.Component {
render() {
const mouse = this.props.mouse;
return (
<img src="/cat.jpg" style={{ position: 'absolute', left: mouse.x, top: mouse.y }} />
);
}
}
class Mouse extends React.Component {
constructor(props) {
super(props);
this.handleMouseMove = this.handleMouseMove.bind(this);
this.state = { x: 0, y: 0 };
}
handleMouseMove(event) {
this.setState({
x: event.clientX,
y: event.clientY
});
}
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
{/*
Instead of providing a static representation of what <Mouse> renders,
use the `render` prop to dynamically determine what to render.
*/}
{this.props.render(this.state)}
</div>
);
}
}
class MouseTracker extends React.Component {
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<Mouse render={mouse => (
<Cat mouse={mouse} />
)}/>
</div>
);
}
}
render props 與HOC( 高階組件)組合
class Mouse extends React.Component {
constructor(props) {
super(props);
this.handleMouseMove = this.handleMouseMove.bind(this);
this.state = { x: 0, y: 0 };
}
handleMouseMove(event) {
this.setState({
x: event.clientX,
y: event.clientY
});
}
render() {
return (
<div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
{this.props.render(this.state)}
</div>
);
}
}
function withMouse(Component) {
return class extends React.Component {
render() {
return (
<Mouse render={mouse => (
<Component {...this.props} mouse={mouse} />
)}/>
);
}
}
}
儘管之前的例子使用了 render,我們也可以簡單地使用 xxxx prop!
使用PureComponent的一個常見問題
class Mouse extends React.PureComponent {
}
class MouseTracker extends React.Component {
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<Mouse render={mouse => (
<Cat mouse={mouse} />
)}/>
</div>
);
}
}
在這樣例子中,每次 <MouseTracker>
渲染,它會生成一個新的函數作爲<Mouse render>
的 prop,因而在同時也抵消了繼承自 React.PureComponent 的<Mouse>
組件的效果!
爲了繞過這一問題,有時你可以定義一個 prop 作爲實例方法,類似如下:
class MouseTracker extends React.Component {
constructor(props) {
super(props);
this.renderTheCat = this.renderTheCat.bind(this);
}
renderTheCat(mouse) {
return <Cat mouse={mouse} />;
}
render() {
return (
<div>
<h1>Move the mouse around!</h1>
<Mouse render={this.renderTheCat} />
</div>
);
}
}
新特性 React Hooks 也可解決類似問題 https://juejin.im/post/5be3ea136fb9a049f9121014
參考鏈接https://react.docschina.org/docs/render-props.html#%E5%9C%A8%E4%BA%A4%E5%8F%89%E5%85%B3%E6%B3%A8%E7%82%B9%EF%BC%88cross-cutting-concerns%EF%BC%89%E4%BD%BF%E7%94%A8-render-props