1.不使用redux實現
如果不使用redux,僅僅依靠react去實現Counter功能是極其簡單的。代碼如下:
index.js
import React from 'react';
import ReactDOM from 'react-dom';
import Counter from './components/Counter';
const render = ()=> ReactDOM.render(
<Counter/>,
document.getElementById("root")
);
render();
components/Counter.js
import React, {Component} from 'react';
class Counter extends Component {
constructor(props) {
super(props);
this.state = {
counter: 0
};
this.add = this.add.bind(this);
this.addOdd = this.addOdd.bind(this);
this.addAsync = this.addAsync.bind(this);
this.minus = this.minus.bind(this);
}
add() {
this.setState({
counter: ++this.state.counter
})
}
addOdd() {
let counter = this.state.counter;
if (counter % 2 === 1) {
this.setState({
counter: ++counter
})
}
}
addAsync() {
setTimeout(this.add, 1000);
}
minus() {
this.setState({
counter: --this.state.counter
})
}
render() {
return (
<div>
Clicked:{this.state.counter} times
{' '}
<button onClick={this.add}>+</button>
{' '}
<button onClick={this.minus}>-</button>
{' '}
<button onClick={this.addOdd}>Increment if odd</button>
{' '}
<button onClick={this.addAsync}>Increment async</button>
</div>
)
}
}
export default Counter;
僅僅兩個文件就可以實現,Counter功能。那爲啥非要引入Redux呢?從自己僅有的這點react經驗來看:1.本例中的狀態只有counter一個,如果應用足夠複雜,在組件內部自己管理狀態,而這些狀態又會影響其他子組件。爲管理這個狀態而編寫的代碼量將會難以閱讀和維護,添加新功能也會很麻煩。2.通過用戶事件去改變狀態,本身沒錯,但是這些狀態沒有統一的操作去統一的state數據結構。redux就是想讓狀態統一管理,統一執行action操作,讓 state 的變化變得可預測
2.使用redux
下面是加入redux之後的項目代碼:
多了一個reducers/index.js文件。
export default (state =0,action) =>{
switch (action.type){
case "INCREASE":
return state+1;
case "DECREASE":
return state-1;
default:
return state;
}
}
src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import Counter from './components/Counter';
import {createStore} from 'redux';
import counter from './reducers';
const store = createStore(counter);
const render = ()=> ReactDOM.render(
/*返回應用當前的 state 樹,它與 store 的最後一個 reducer 返回值相同。*/
<Counter counter={store.getState()}
add={()=>store.dispatch({type:'INCREASE'})}
minus={()=>store.dispatch({type:'DECREASE'})}
/>,
document.getElementById("root")
);
render();
store.subscribe(render);
components/Counter.js
import React, {Component} from 'react';
import PropTypes from 'prop-types';
class Counter extends Component {
constructor(props) {
super(props);
this.addOdd = this.addOdd.bind(this);
this.addAsync = this.addAsync.bind(this);
}
addOdd() {
let counter = this.props.counter;
if (counter % 2 === 1) {
this.props.add()
}
}
addAsync() {
setTimeout(this.props.add, 1000);
}
render() {
const { counter, add, minus } = this.props;
return (
<div>
Clicked:{counter} times
{' '}
<button onClick={add}>+</button>
{' '}
<button onClick={minus}>-</button>
{' '}
<button onClick={this.addOdd}>Increment if ODD</button>
{' '}
<button onClick={this.addAsync}>Increment async</button>
</div>
)
}
}
//嚴格定義參數類型
Counter.propTypes = {
counter: PropTypes.number.isRequired,
add: PropTypes.func.isRequired,
minus: PropTypes.func.isRequired
};
export default Counter;
在使用redux之後,Counter,中的狀態管理被統一到store中,通過store.dispatch(action)的方法唯一的去修改state內容,具體的:會使用當前 getState() 的結果和傳入的 action 以同步方式的調用 store 的 reduce 函數。返回值會被作爲下一個 state。從現在開始,這就成爲了 getState() 的返回值,同時變化監聽器(change listener)會被觸發。