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关于前端:从源码对reactrouter-v5进行原理分析二

作者：

jiezi

在

目录

  • 前言
  • react-router构造剖析
  • BrowserHistory
  • Router
  • Switch
  • Route

前言

此篇文章默认读者曾经理解react-router的api应用办法;

在看这篇文章之前, 须要先对react-router和react-router-dom有一个简略的理解;

首先来看官网对两者的形容

The core of React Router (react-router)

DOM bindings for React Router (react-router-dom)

react-router是React Router的外围, 实现了路由的外围性能;

react-router-dom是React Router的DOM绑定, 提供了浏览器环境下的性能, 比方Link, BrowserRouter等组件;

能够了解为, react-router-dom基于react-router, 装置依赖的时候只须要装置react-router-dom就好了!

react-router构造剖析

依据官网文档, 应用react-router-dom进行路由治理, 首先咱们抉择一个路由模式:

  • BrowserRouter: History模式
  • HashRouter: Hash模式
  • MemoryRouter: 在没有url的状况下, 应用Memory记住路由, 常见在React Native中应用, 这里不进行探讨

以下都以create-react-app为例

这里抉择History模式, 也就是在最外层应用BrowserRouter组件:

index.tsx

import React from 'react';
import ReactDOM from 'react-dom';
import {BrowserRouter as Router} from 'react-router-dom';
import App from './App';

ReactDOM.render(
  <Router>
    <App />
  </Router>,
  document.getElementById('root')
);

而后在被BrowserHistory组件包裹的组件中能够应用Route进行路由划分:

App.tsx

import React from 'react';
import {Route} from 'react-router-dom';

const Page1.React.FC = props => {
  return <div>Page1</div>;
};

const Page2.React.FC = props => {
  return <div>Page2</div>;
};

function App() {
  return (
    <div className="App">
      <Route path="/page1" component={Page1}></Route>
      <Route path="/page2" component={Page2}></Route>
    </div>
  );
}

export default App;

以上就是react-router的大略构造, 上面将对react-router-dom的组件进行源码剖析

BrowserHistory

BrowserHistory和HashHistory的代码构造和逻辑类似, 这里只对BrowserHistory作剖析;

BrowserHistory外围代码逻辑剖析:

定义BrowserHistory传入的prop类型

import PropTypes from "prop-types";

class BrowserRouter extends React.Component {
  // 此处代码略去
}

BrowserRouter.propTypes = {
  basename: PropTypes.string,
  children: PropTypes.node,
  forceRefresh: PropTypes.bool,
  getUserConfirmation: PropTypes.func,
  keyLength: PropTypes.number
};

应用history的createBrowserHistory, 将props作为参数, 创立一个history实例, 并将history传入Router组件中

import { Router } from "react-router";
import { createBrowserHistory as createHistory } from "history";

class BrowserRouter extends React.Component {
  history = createHistory(this.props);

    render() {
    return <Router history={this.history} children={this.props.children} />;
  }
}

从源码中能够看出, BrowserHistory只是对Router组件的简略包装;

Router

react-router-dom中的Router实际上就是react-router的Router, 此处间接对react-router的Router进行源码剖析:

定义Router传入的props类型:

import PropTypes from "prop-types";

Router.propTypes = {
  children: PropTypes.node,
  history: PropTypes.object.isRequired,
  staticContext: PropTypes.object
};

staticContext是staticRouter中传入Router的属性, 源码中所有应用了props.staticContext的代码都不做探讨;

Router的构造函数中,申明this.state.location, 应用history.listen对history.location进行监听, 并将history.listen的返回值(用于移除监听事件)赋值给this.unlisten, 在componentWillUnmount生命周期中进行调用;

之所以在构造函数中就对history.location进行监听, 而不是在componentDidMount中进行监听, 官网是这么解释的:

This is a bit of a hack. We have to start listening for location changes here in the constructor in case there are any <Redirect>s on the initial render. If there are, they will replace/push when they mount and since cDM fires in children before parents, we may get a new location before the <Router> is mounted.

大略意思就是, 因为子组件会比父组件更早渲染实现, 并且因为Redirect的存在, 若是在Router的componentDidMount中对history.location进行监听, 则有可能在监听事件注册之前, history.location曾经因为Redirect组件产生了屡次扭转, 因而咱们须要在Router的constructor中就注册监听事件;

import React from 'react';

class Router extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      location: props.history.location
    };

    // This is a bit of a hack. We have to start listening for location
    // changes here in the constructor in case there are any <Redirect>s
    // on the initial render. If there are, they will replace/push when
    // they mount and since cDM fires in children before parents, we may
    // get a new location before the <Router> is mounted.
    this._isMounted = false;
    this._pendingLocation = null;

    if (!props.staticContext) { // props.staticContext不存在, 因而默认为true
      this.unlisten = props.history.listen(location => {
        if (this._isMounted) {
          this.setState({ location });
        } else {
          this._pendingLocation = location;
        }
      });
    }
  }
  
  componentDidMount() {
    this._isMounted = true;

    if (this._pendingLocation) {
      this.setState({ location: this._pendingLocation });
    }
  }

  componentWillUnmount() {
    if (this.unlisten) {
      this.unlisten();
      this._isMounted = false;
      this._pendingLocation = null;
    }
  }
  
  // 以下代码省略
}

react-router中应用context进行组件通信; 在Router中, 应用RouterContext.Provider进行router数据(history,location, match以及staticContext)传递, 应用HistoryContext.Provider进行history数据传递, 子组件(Route或是Redirect等)能够通过RouterContext.Consumer或是HistoryContext.Consumer对下层数据进行接管; HistoryContext和RouterContext都是应用mini-create-react-context的createContext办法创立的context, mini-create-react-context工具库本身定义如下:

(A smaller) Polyfill for the React context API

mini-create-react-context是React context API的Polyfil, 因而能够间接将mini-create-react-context当成React context API;

import React from "react";
import HistoryContext from "./HistoryContext.js";
import RouterContext from "./RouterContext.js";

class Router extends React.Component {
  static computeRootMatch(pathname) {
    return { path: "/", url: "/", params: {}, isExact: pathname === "/" };
  }

  render() {
    return (
      <RouterContext.Provider
        value={{
          history: this.props.history,
          location: this.state.location,
          match: Router.computeRootMatch(this.state.location.pathname),
          staticContext: this.props.staticContext
        }}
        >
        <HistoryContext.Provider
          children={this.props.children || null}
          value={this.props.history}
        />
      </RouterContext.Provider>
    );
  }
}

Switch

<Switch> is unique in that it renders a route exclusively

即便有多个路由组件胜利匹配, Switch也只展现一个路由;

<Switch>必须作为<Router>的子组件进行应用, 若是脱离<Router>, 则会报错:

"You should not use <Switch> outside a <Router>"

定义Switch中传入的props类型:

import PropTypes from "prop-types";

Switch.propTypes = {
  children: PropTypes.node,
  location: PropTypes.object
};

应用RouterContext.Consumer接管RouterContext.Provider的路由信息; Switch对路由组件进行程序匹配, 应用React.Children.forEach对Switch子组件进行遍历, 每次遍历逻辑如下:

  1. 应用React.isValidElement判断子组件是否为无效的element:

    • 无效: 则进入步骤二;
    • 有效: 完结此轮循环, 进行下一轮循环;

  2. 申明path:

    const path = child.props.path || child.props.from;

    注: <Route>应用path进行路由地址申明, <Redirect>应用from进行重定向起源地址申明;

    接着判断path是否存在:

    • 存在path的状况下, 示意子组件存在路由映射关系, 应用matchPath对path进行匹配, 判断路由组件的门路与以后location.pathname是否匹配: 若是匹配, 则对子组件进行渲染, 并将matchPath返回的值作为computedMatch传递到子组件中, 并且不再对其余组件进行渲染; 若是不匹配, 则间接进行下次循环; 留神: location能够是内部传入的props.location, 若是props.location不存在, 则为context.location;
    • 不存在path的状况下, 示意子组件不存在路由映射关系, 间接渲染该子组件, 并将context.match作为computedMatch传入子组件中;

matchPath是react-router的一个api, 源码中正文对matchPath的介绍如下:

Public API for matching a URL pathname to a path.

次要用于匹配路由, 匹配胜利则返回一个match, 若是匹配失败, 则返回null;

import React from 'react';
import RouterContext from "./RouterContext.js";
import matchPath from "./matchPath.js";

/**
 * The public API for rendering the first <Route> that matches.
 */
class Switch extends React.Component {
  render() {
    return (
      <RouterContext.Consumer>
        {context => {
          invariant(context, "You should not use <Switch> outside a <Router>");

          const location = this.props.location || context.location;

          let element, match;

          // We use React.Children.forEach instead of React.Children.toArray().find()
          // here because toArray adds keys to all child elements and we do not want
          // to trigger an unmount/remount for two <Route>s that render the same
          // component at different URLs.
          React.Children.forEach(this.props.children, child => {
            if (match == null && React.isValidElement(child)) {
              element = child;

              const path = child.props.path || child.props.from;

              match = path
                ? matchPath(location.pathname, { ...child.props, path })
                : context.match;
            }
          });

          return match
            ? React.cloneElement(element, { location, computedMatch: match })
            : null;
        }}
      </RouterContext.Consumer>
    );
  }
}

Route

The Route component is perhaps the most important component in React Router to understand and learn to use well. Its most basic responsibility is to render some UI when its path matches the current URL

<Route>可能是react-router中最重要的组件, 它最根本的职责是在其门路与以后URL匹配时出现对应的UI组件;

与其余非Router组件一样, 若是不被<RouterContext.Provider>包裹, 则会报错:

"You should not use <Switch> outside a <Router>"

定义Route的props类型:

import PropTypes from "prop-types";

Route.propTypes = {
  children: PropTypes.oneOfType([PropTypes.func, PropTypes.node]),
  component: (props, propName) => {
    if (props[propName] && !isValidElementType(props[propName])) {
      return new Error(
        `Invalid prop 'component' supplied to 'Route': the prop is not a valid React component`
      );
    }
  },
  exact: PropTypes.bool,
  location: PropTypes.object,
  path: PropTypes.oneOfType([
    PropTypes.string,
    PropTypes.arrayOf(PropTypes.string)
  ]),
  render: PropTypes.func,
  sensitive: PropTypes.bool,
  strict: PropTypes.bool
};

与其它路由组件一样, 应用RouterContext.Consumer接管全局路由信息; 因为Route的逻辑比较简单, 次要判断path与以后路由是否匹配, 若是匹配则进行渲染对应路由组件, 若是不匹配则不进行渲染, 外围代码如下:

const match = this.props.computedMatch
  ? this.props.computedMatch // <Switch> already computed the match for us
  : this.props.path
  ? matchPath(location.pathname, this.props)
  : context.match;

...

<RouterContext.Provider value={props}>
  {
    props.match
    ? children
      ? typeof children === "function"
          ? __DEV__
              ? evalChildrenDev(children, props, this.props.path)
                : children(props)
            : children
        : component
          ? React.createElement(component, props)
            : render
              ? render(props)
                : null
    : typeof children === "function"
      ? __DEV__
          ? evalChildrenDev(children, props, this.props.path)
            : children(props)
        : null
  }
</RouterContext.Provider>

注: 依据下面代码, 不管props.match是否为true, 当Route的children为函数时都会进行渲染;

总结

本篇文章对react-router的局部外围组件进行源码解读; react-router应用Context.Provider向路由树传递路由信息, Route等组件通过Context.Consumer接管路由信息, 匹配门路并渲染路由组件, 以及与上篇文章讲到的history的紧密配合, 才让react-router如此优良; 下一篇文章将对残余组件以及react-router的hooks进行源码解读!

如果发现文章有谬误能够在评论区里留言哦, 欢送斧正!

上一篇文章: 从源码对react-router v5进行原理剖析(一)
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