Hook 簡介
官方原話:Hook 是 React 16.8 的新增特性。它可以讓你在不編寫 class 的情況下使用 state 以及其他的 React 特性。
隨着 Hook API 的發佈,使得函數式組件生態也逐漸豐富起來,Github 上基於 Hook 封裝的組件庫也不斷增多。
今天就來說說 [mobx-react-lite](https://github.com/mobxjs/mobx-react-lite)
,它是基於 React 16.8
和 Hooks
的 MobX
的輕量級React綁定。
這裏通過 mobx + mobx-react
與 mobx-react-lite + Context API
兩種使用方式對比說明
mobx的使用
- 創建
store
// store.js
import {observable, action} from 'mobx';
class Store {
@observable
count = 0;
@action
handleCount() {
this.count += 1;
}
}
export default new Store();
- 根組件通過
Provider
注入store
function App() {
return (
<Provider store={store}>
<div className="App">
<CounterClass></CounterClass>
<CounterFunction></CounterFunction>
</div>
</Provider>
);
}
export default App;
- 類組件(class)訪問
store
import React, { Component } from 'react';
import {inject, observer} from 'mobx-react';
import {toJS} from 'mobx'; // 查看store中原始JavaScript數據結構
@inject('store')
@observer
class CounterClass extends Component {
handleClick = () => {
this.props.store.handleCount();
};
render() {
console.log(toJS(this.props.store));
return (
<div>
count: {this.props.store.count}
<button onClick={this.handleClick}>add one</button>
</div>
)
}
}
export default CounterClass;
- 函數組件使用
store
import React from 'react'
import {inject, observer} from 'mobx-react';
const CounterFunction = ({store}) => {
return (
<div>
<p>you clicked {store.count} times</p>
<button onClick={() => store.handleCount()}>Add</button>
</div>
);
}
export default inject('store')(observer(CounterFunction));
mobx-react-lite 基於 Hook API 的使用
- 創建
Counter store
組件
// HookStore.js
import React, {createContext} from 'react';
import {useLocalStore, observer} from 'mobx-react-lite';
export const MyContext = createContext(null);
export const Counter = observer((props) => {
const store = useLocalStore(() => (
{
count: 1,
get getCount() {
return store.count;
},
handleCount() {
store.count += 2;
}
}
));
return (
<MyContext.Provider value={store}>
{props.children}
</MyContext.Provider>
);
});
- 使用
Counter
組件,子組件是class類組件時,通過MyContext.Consumer
訪問store
,函數組件通過useContext
Hook API 訪問store
import React from 'react';
import {Counter} from './store/HookStore';
import './App.scss';
function App() {
return (
<div className="App">
<Counter>
<HookDemo01></HookDemo01>
<ClassCom></ClassCom>
</Counter>
</div>
);
}
export default App;
- 類組件(class)連接
store
import React, { Component } from 'react';
import {Observer} from 'mobx-react-lite';
import {MyContext} from '../store/HookStore';
import {toJS} from 'mobx';
class CounterClass extends Component {
render() {
return (
<div>
<MyContext.Consumer>
{
store => {
{/* 使用 Object.is 比較store是否發生變化,store的引用不變,導致不會重渲染,獲取最新依賴值需使用 Observer 組件 */}
console.log('store: ', toJS(store));
return (
<>
<p>counter2: {store.count}</p> {/* 這種方式在 class 組件中無效,不會引發重渲染 */}
<Observer>{() => <p>counter2: {store.count}</p>}</Observer> {/* 必須這樣寫,Observer 組件是mobx-react-lite提供的唯一可在類組件中使用的組件 */}
<button onClick={() => store.handleCount()}>Counter Add</button>
</>
)
}
}
</MyContext.Consumer>
</div>
)
}
}
export default CounterClass;
- 函數組件連接
store
import React, {useState, useEffect, useContext} from 'react'
import {Observer, observer} from 'mobx-react-lite';
import {MyContext} from '../../store/HookStore';
const CounterFunction = (props) => {
const [num, setNum] = useState(10);
const store = useContext(MyContext); // 當組件上層最近的 <MyContext.Provider> 更新時,該 Hook 會觸發重渲染,並使用最新傳遞給 MyContext provider 的 context value 值。
useEffect(() => {
console.log('num change', MyContext);
}, [num]);
return (
<div>
<p>num: {num}</p>
<button onClick={() => setNum(num + 1)}>set num</button>
{/* 深度監聽 store 變化並進行重渲染,導致下面兩行結果相同 */}
<p>Count: {store.getCount}</p>
<Observer>{() => <p>Count2: {store.getCount}</p>}</Observer>
<button onClick={() => store.handleCount()}>Counter Add</button>
</div>
);
}
export default observer(CounterFunction);