Reactルーターの完全な初心者向けガイド(ルーターフックを含む)

Reactは、ユーザーインターフェイスを構築するためのJavaScriptライブラリです。React Routerを使用して、複数ページのアプリケーションを構築するように拡張することもできます。これは、Reactアプリでのルーティングを可能にするサードパーティのライブラリです。

このチュートリアルでは、ReactRouterを使い始めるために知っておく必要のあるすべてをカバーします。

  • プロジェクトの設定
  • ルーティングとは何ですか?
  • ルーターの設定
  • レンダリングルート
  • リンクを使用してページを切り替える
  • ルートパラメータの受け渡し
  • プログラムによるナビゲート
  • 別のページにリダイレクトする
  • 404ページへのリダイレクト
  • ルートの保護
  • ルーターフック
  • useHistory
  • useParams
  • useLocation
  • 最終的な考え
  • 次のステップ

プロジェクトの設定

フォローできるようにするには、ターミナルで次のコマンドを実行して、新しいReactアプリを作成する必要があります。

npx create-react-app react-router-guide 

次に、次のコード行をApp.jsファイルに追加します。

import React from "react"; import "./index.css" export default function App() { return (   
  • Home
  • About
  • Contact
); } // Home Page const Home = () => (

Home

); // About Page const About = () => (

About

); // Contact Page const Contact = () => (

Contact

); const FakeText = () => (

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

)

次に、準備ができたら、重要な質問に答えることから始めましょう:ルーティングとは何ですか?

ルーティングとは何ですか?

ルーティングは、ユーザーにさまざまなページを表示する機能です。つまり、ユーザーはURLを入力するか要素をクリックすることで、アプリケーションのさまざまな部分間を移動できます。

ご存知かもしれませんが、デフォルトでは、Reactはルーティングなしで提供されます。プロジェクトで有効にするには、react-routerという名前のライブラリを追加する必要があります。

これをインストールするには、ターミナルで次のコマンドを実行する必要があります。

yarn add react-router-dom 

または

npm install react-router-dom 

これでルーターが正常にインストールされました。次のセクションでルーターの使用を開始しましょう。

興奮している

ルーターの設定

インポートに私たちのリアクトアプリ、我々まず必要でルーティングを有効にするにはBrowserRouterからreact-router-dom

App.js、ファイル、次のように入力します。

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router } from "react-router-dom"; export default function App() { return (    
  • Home
  • About
  • Contact
); }

This should hold everything in our app where routing is needed. That means, if we need routing in our entire app, we must wrap our higher component with BrowserRouter.

By the way, you don't have to rename BrowserRouter as Router as I do here, I just want to keep things readable.

A router alone doesn't do much. So let's add a route in the next section.

Rendering routes

To render routes, we have to import the Route component from the router package.

In your App.js file, add the following code:

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route } from "react-router-dom"; export default function App() { return (    
  • Home
  • About
  • Contact

Welcome!

} /> ); }

Then, add it where we want to render the content. The Route component has several properties. But here, we just need path and render.

path: the path of the route. Here, we use / to define the path of the home page.

render: will display the content whenever the route is reached. Here, we'll render a welcome message to the user.

In some cases serving routes like that is perfectly fine. But imagine a case when we have to deal with a real component – using render may not be the right solution.

So, how can we display a real component? Well, the Route component has another property named component.

Let's update our example a bit to see it in action.

In your App.js file, add the following code:

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route } from "react-router-dom"; export default function App() { return (    
  • Home
  • About
  • Contact
); } const Home = () => (

Home

);

Now, instead of rendering a message, our route will load the Home component.

To get the full power of React Router, we need to have multiple pages and links to play with. We already have pages (components if you want, too), so now let's add some links so we can switch between pages.

Using links to switch pages

To add links to our project, we will use the React Router again.

In your App.js file, add the following code:

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route, Link } from "react-router-dom"; export default function App() { return (    
  • Home
  • About
  • Contact
); } const Home = () => (

Home

); const About = () => (

About

); const Contact = () => (

Contact

);

After importing Link, we have to update our navigation bar a bit. Now, instead of using a tag and href, React Router uses Link and to to, well, be able to switch between pages without reloading it.

Then, we need to add two new routes, About and Contact, to be able to switch between pages or components.

Now, we can go to different parts of our app through links. But there is an issue with our router: the Home component is always displayed even if we switch to other pages.

This is because React Router will check if the path defined starts with /. If that's the case, it will render the component. And here, our first route starts with /, so the Home component will be rendered each time.

However, we can still change the default behavior by adding the exact property to Route.

In App.js, add:

By updating the Home route with exact, now it will be rendered only if it matches the full path.

We can still enhance it by wrapping our routes with Switch to tell to React Router to load only one route at a time.

In App.js, add:

import { BrowserRouter as Router, Route, Link, Switch } from "react-router-dom";      

Now that we have new links, let's use them to pass parameters.

Passing route parameters

To pass data between pages, we have to update our example.

In your App.js file, add the following code:

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route, Link, Switch } from "react-router-dom"; export default function App() { const name = 'John Doe' return (    
  • Home
  • About
  • Contact
); } const Home = () => (

Home

); const About = ({match:{params:{name}}}) => ( // props.match.params.name

About {name}

); const Contact = () => (

Contact

);

As you can see here, we start by declaring a new constant name which will be passed as a parameter to the About page. And we append name to the corresponding link.

With that, we now have to update the About route by adjusting its path to receive name as a parameter path="/about/:name".

Now, the parameter will be received as props from the About component. The only thing we have to do now is destructure the props and get back the name property. By the way, {match:{params:{name}}} is the same as props.match.params.name.

We've done a lot up to this point. But in some cases we don't want to use links to navigate between pages.

Sometimes, we have to wait for an operation to finish before navigating to the next page.

同意する

So, let's handle that case in the next section.

Navigating programmatically

The props we receive have some convenient methods we can use to navigate between pages.

In App.js, add:

const Contact = ({history}) => (  

Contact

history.push('/') } >Go to home );

Here, we pull the history object from the props we receive. It has some handy methods like goBack, goForward, and so on. But here, we will use the push method to be able to go to the Home page.

Now, let's handle the case when we want to redirect our user after an action.

Redirecting to another page

The React Router has another component named Redirect. As you guessed, it helps us redirect the user to another page

In App.js, add:

import { BrowserRouter as Router, Route, Link, Switch, Redirect } from "react-router-dom"; const About = ({match:{params:{name}}}) => ( // props.match.params.name  { name !== 'John Doe' ?  : null } 

About {name}

);

Now, if the name passed as a parameter is not equal to John Doe, the user will be redirected to the home page.

You could argue that you should redirect the user with props.history.push('/). Well, the Redirect component replaces the page and therefore the user can't go back to the previous page. But, with the push method they can. However, you can use props.history.replace('/) to mimic the Redirect behavior.

Now let's move on and handle the case when the user hits a route that doesn't exist.

Redirecting to a 404 page

To redirect the user to a 404 page, you can create a component to show it. But here, to keep things simple, I will just display a message with render.

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route, Link, Switch } from "react-router-dom"; export default function App() { const name = 'John Doe' return (    
  • Home
  • About
  • Contact

404: page not found

} /> ); }

The new route we've added will catch every path that doesn't exist and redirect the user to the 404 page.

Now, let's move on and learn how to protect our routes in the next section.

Guarding routes

There are many ways to protect routes to React. But here I will just check if the user is authenticated and redirect them to the appropriate page.

import React, { Fragment } from "react"; import "./index.css" import { BrowserRouter as Router, Route, Link, Switch } from "react-router-dom"; export default function App() { const name = 'John Doe' const isAuthenticated = false return (    
  • Home
  • About
  • Contact
{ isAuthenticated ? : } ); }

As you can see here, I declared a variable to mimic authentication. Then, check if the user is authenticated or not. If they are, render protected pages. Otherwise redirect them to the home page.

We've covered a lot up to this point, but an interesting part remains: router hooks.

Let's move to the final section and introduce Hooks.

はい

Router Hooks

Router hooks make things much easier. Now you can access the history, location, or parameters in an easy and elegant way.

useHistory

The useHistory hook gives us access to the history instance without pulling it from props.

import { useHistory } from "react-router-dom"; const Contact = () => { const history = useHistory(); return (  

Contact

history.push('/') } >Go to home ) };

useParams

This hook helps us get the parameter passed on the URL without using the props object.

import { BrowserRouter as Router, Route, Link, Switch, useParams } from "react-router-dom"; export default function App() { const name = 'John Doe' return (    
  • Home
  • About
); } const About = () => { const { name } = useParams() return ( // props.match.params.name { name !== 'John Doe' ? : null }

About {name}

) };

useLocation

このフックは、現在のURLを表すロケーションオブジェクトを返します。

import { useLocation } from "react-router-dom"; const Contact = () => { const { pathname } = useLocation(); return (  

Contact

Current URL: {pathname}

) };

最終的な考え

React Routerは、優れたユーザビリティを備えた単一ページから複数ページのアプリケーション感覚に移行するのに役立つ素晴らしいライブラリです。(覚えておいてください–結局のところ、それはまだシングルページアプリです)。

そして今、ルーターフックで、あなたはそれらがどれほど簡単でエレガントであるかを見ることができます。それらは間違いなくあなたの次のプロジェクトで考慮すべきものです。

あなたは私のブログで私の記事の詳細を読むことができます。

次のステップ

Reactルーターのドキュメント

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