react缓存页面react-keepalive-router

Posted 2023-04-30

参考技术A https://blog.csdn.net/sinat_17775997/article/details/123211231

React中实现keepalive组件缓存效果

背景：由于react官方并没有提供缓存组件相关的api（类似vue中的keepalive），在某些场景，会使得页面交互性变的很差，比如在有搜索条件的表格页面，点击某一条数据跳转到详情页面，再返回表格页面，会重新请求数据，搜索条件也将清空，用户得重新输入搜索条件，再次请求数据，大大降低办公效率，如图：

目标：封装keepalive缓存组件，实现组件的缓存，并暴露相关方法，可以手动清除缓存。

版本：React 17，react-router-dom 5

结构：

代码：

cache-types.js

// 缓存状态
export const CREATE = 'CREATE';        // 创建
export const CREATED = 'CREATED';      // 创建成功
export const ACTIVE = 'ACTIVE';        // 激活
export const DESTROY = 'DESTROY';      // 销毁

 CacheContext.js

import React from 'react';
const CacheContext = React.createContext();
export default CacheContext;

cacheReducer.js

import * as cacheTypes from "./cache-types";
function cacheReducer(cacheStates = ,  type, payload ) 
  switch (type) 
    case cacheTypes.CREATE:
      return 
        ...cacheStates,
        [payload.cacheId]: 
          scrolls: ,              // 缓存滚动条，key: dom, value: scrollTop
          cacheId: payload.cacheId, // 缓存Id
          element: payload.element, // 需要渲染的虚拟DOM
          doms: undefined,          // 当前的虚拟dom所对应的真实dom
          status: cacheTypes.CREATE,// 缓存状态
        ,
      ;
    case cacheTypes.CREATED:
      return 
        ...cacheStates,
        [payload.cacheId]: 
          ...cacheStates[payload.cacheId],
          doms: payload.doms,
          status: cacheTypes.CREATED,
        ,
      ;
    case cacheTypes.ACTIVE:
      return 
        ...cacheStates,
        [payload.cacheId]: 
          ...cacheStates[payload.cacheId],
          status: cacheTypes.ACTIVE,
        ,
      ;
    case cacheTypes.DESTROY:
      return 
        ...cacheStates,
        [payload.cacheId]: 
          ...cacheStates[payload.cacheId],
          status: cacheTypes.DESTROY,
        ,
      ;
    default:
      return cacheStates;
  

export default cacheReducer;

KeepAliveProvider.js

import React,  useReducer, useCallback  from "react";
import CacheContext from "./CacheContext";
import cacheReducer from "./cacheReducer";
import * as cacheTypes from "./cache-types";
function KeepAliveProvider(props) 
  let [cacheStates, dispatch] = useReducer(cacheReducer, );
  const mount = useCallback(
    ( cacheId, element ) => 
      // 挂载元素方法，提供子组件调用挂载元素
      if (cacheStates[cacheId]) 
        let cacheState = cacheStates[cacheId];
        if (cacheState.status === cacheTypes.DESTROY) 
          let doms = cacheState.doms;
          doms.forEach((dom) => dom.parentNode.removeChild(dom));
          dispatch( type: cacheTypes.CREATE, payload:  cacheId, element  ); // 创建缓存
        
       else 
        dispatch( type: cacheTypes.CREATE, payload:  cacheId, element  ); // 创建缓存
      
    ,
    [cacheStates]
  );
  let handleScroll = useCallback(
    // 缓存滚动条
    (cacheId,  target ) => 
      if (cacheStates[cacheId]) 
        let scrolls = cacheStates[cacheId].scrolls;
        scrolls[target] = target.scrollTop;
      
    ,
    [cacheStates]
  );
  return (
    <CacheContext.Provider
      value= mount, cacheStates, dispatch, handleScroll 
    >
      props.children
      /* cacheStates维护所有缓存信息， dispatch派发修改缓存状态*/
      Object.values(cacheStates)
        .filter((cacheState) => cacheState.status !== cacheTypes.DESTROY)
        .map(( cacheId, element ) => (
          <div
            id=`cache_$cacheId`
            key=cacheId
            // 原生div中声明ref，当div渲染到页面，会执行ref中的回调函数，这里在id为cache_$cacheId的div渲染完成后，会继续渲染子元素
            ref=(dom) => 
              let cacheState = cacheStates[cacheId];
              if (
                dom &&
                (!cacheState.doms || cacheState.status === cacheTypes.DESTROY)
              ) 
                let doms = Array.from(dom.childNodes);
                dispatch(
                  type: cacheTypes.CREATED,
                  payload:  cacheId, doms ,
                );
              
            
          >
            element
          </div>
        ))
    </CacheContext.Provider>
  );

const useCacheContext = () => 
  const context = React.useContext(CacheContext);
  if (!context) 
    throw new Error("useCacheContext必须在Provider中使用");
  
  return context;
;
export  KeepAliveProvider, useCacheContext ;

withKeepAlive.js

import React,  useContext, useRef, useEffect  from "react";
import CacheContext from "./CacheContext";
import * as cacheTypes from "./cache-types";
function withKeepAlive(
  OldComponent,
   cacheId = window.location.pathname, scroll = false 
) 
  return function (props) 
    const  mount, cacheStates, dispatch, handleScroll  =
      useContext(CacheContext);
    const ref = useRef(null);
    useEffect(() => 
      if (scroll) 
        // scroll = true, 监听缓存组件的滚动事件，调用handleScroll()缓存滚动条
        ref.current.addEventListener(
          "scroll",
          handleScroll.bind(null, cacheId),
          true
        );
      
    , [handleScroll]);
    useEffect(() => 
      let cacheState = cacheStates[cacheId];
      if (
        cacheState &&
        cacheState.doms &&
        cacheState.status !== cacheTypes.DESTROY
      ) 
        // 如果真实dom已经存在，且状态不是DESTROY，则用当前的真实dom
        let doms = cacheState.doms;
        doms.forEach((dom) => ref.current.appendChild(dom));
        if (scroll) 
          // 如果scroll = true, 则将缓存中的scrollTop拿出来赋值给当前dom
          doms.forEach((dom) => 
            if (cacheState.scrolls[dom])
              dom.scrollTop = cacheState.scrolls[dom];
          );
        
       else 
        // 如果还没产生真实dom，派发生成
        mount(
          cacheId,
          element: <OldComponent ...props dispatch=dispatch />,
        );
      
    , [cacheStates, dispatch, mount, props]);
    return <div id=`keepalive_$cacheId` ref=ref />;
  ;

export default withKeepAlive;

index.js

export  KeepAliveProvider  from "./KeepAliveProvider";
export default as withKeepAlive from './withKeepAlive';

使用：

　　1.用<KeepAliveProvider></KeepAliveProvider>将目标缓存组件或者父级包裹；

　　2.将需要缓存的组件，传入withKeepAlive方法中，该方法返回一个缓存组件；

　　3.使用该组件；

App.js

import React from "react";
import 
  BrowserRouter,
  Link,
  Route,
  Switch,
 from "react-router-dom";
import Home from "./Home.js";
import List from "./List.js";
import Detail from "./Detail.js";
import  KeepAliveProvider, withKeepAlive  from "./keepalive-cpn";

const KeepAliveList = withKeepAlive(List,  cacheId: "list", scroll: true );

function App() 
  return (
    <KeepAliveProvider>
      <BrowserRouter>
        <ul>
          <li>
            <Link to="/">首页</Link>
          </li>
          <li>
            <Link to="/list">列表页</Link>
          </li>
          <li>
            <Link to="/detail">详情页A</Link>
          </li>
        </ul>
        <Switch>
          <Route path="/" component=Home exact></Route>
          <Route path="/list" component=KeepAliveList></Route>
          <Route path="/detail" component=Detail></Route>
        </Switch>
      </BrowserRouter>
    </KeepAliveProvider>
  );


export default App;

效果：

假设有个需求，从首页到列表页，需要清空搜索条件，重新请求数据，即回到首页，需要清除列表页的缓存。

上面的KeepAliveProvider.js中，暴露了一个useCacheContext()的hook，该hook返回了缓存组件相关数据和方法，这里可以用于清除缓存：

Home.js

import React,  useEffect  from "react";
import  DESTROY  from "./keepalive-cpn/cache-types";
import  useCacheContext  from "./keepalive-cpn/KeepAliveProvider";

const Home = () => 
  const  cacheStates, dispatch  = useCacheContext();

  const clearCache = () => 
    if (cacheStates && dispatch) 
      for (let key in cacheStates) 
        if (key === "list") 
          dispatch( type: DESTROY, payload:  cacheId: key  );
        
      
    
  ;
  useEffect(() => 
    clearCache();
    // eslint-disable-next-line
  , []);
  return (
    <div>
      <div>首页</div>
    </div>
  );
;

export default Home;

效果：

至此，react简易版的keepalive组件已经完成啦~

脚踏实地行，海阔天空飞