145 lines
5.4 KiB
Markdown
145 lines
5.4 KiB
Markdown
---
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id: 5a24c314108439a4d4036154
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title: Combine Multiple Reducers
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challengeType: 6
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isRequired: false
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forumTopicId: 301436
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localeTitle: 组合多个 Reduces
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---
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## Description
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<section id='description'>
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当你应用程序的状态开始变得越来越复杂时，将状态划分为多个部分可能是个更好的选择。相反，请记住 Redux 的第一个原则：所有应用程序状态都保存在 store 中的一个简单的 state 对象中。因此，Redux 提供 reducer 组合作为复杂状态模型的解决方案。定义多个 reducer 来处理应用程序状态的不同部分，然后将这些 reducer 组合成一个 root reducer。然后将 root reducer 传递给 Redux <code>createStore()</code>方法。
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为了让我们将可以将多个 reducer 组合在一起，Redux 提供了<code>combineReducers()</code>方法。该方法接受一个对象作为参数，在该参数中定义一个将键与特定 reducer 函数关联的属性。Redux 将使用你给的键值作为关联状态的名称。
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通常情况下，当它们在某种程度上是独一无二的，为每个应用程序的 state 创建一个减少器是一个很好的做法。例如，在一个带有用户身份验证的记笔记应用程序中，一个 reducer 可以处理身份验证而另一个处理用户提交的文本和注释。对于这样的应用程序，我们可能会编写<code>combineReducers()</code>方法，如下所示：
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```js
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const rootReducer = Redux.combineReducers({
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auth: authenticationReducer,
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notes: notesReducer
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});
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```
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现在，<code>notes</code>键将包含与我们的注释相关联的所有状态，并由我们的<code>notesReducer</code>处理。这就是如何组合多个 reducer 来管理更复杂的应用程序状态，在此示例中，Redux store 中保存的状态将是一个包含<code>auth</code>和<code>notes</code>属性的简单对象。
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</section>
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## Instructions
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<section id='instructions'>
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代码编辑器中提供了<code>counterReducer()</code>和<code>authReducer()</code>函数以及 Redux store。使用<code>Redux.combineReducers()</code>方法编写完成<code>rootReducer()</code>函数。将<code>counterReducer</code>分配给一个叫做<code>count</code>的键，将<code>authReducer</code>分配给一个叫做<code>auth</code>的键。
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>counterReducer</code>应该递增和递减<code>state</code>。
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testString: 'assert((function() { const initialState = store.getState().count; store.dispatch({type: INCREMENT}); store.dispatch({type: INCREMENT}); const firstState = store.getState().count; store.dispatch({type: DECREMENT}); const secondState = store.getState().count; return firstState === initialState + 2 && secondState === firstState - 1 })());'
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- text: <code>authenticated</code>的<code>state</code>值应该在<code>true</code>和<code>false</code>之间切换。
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testString: 'assert((function() { store.dispatch({type: LOGIN}); const loggedIn = store.getState().auth.authenticated; store.dispatch({type: LOGOUT}); const loggedOut = store.getState().auth.authenticated; return loggedIn === true && loggedOut === false })());'
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- text: store <code>state</code>应该有两个 key：一个是<code>count</code>，它包含一个数字。另一个<code>auth</code>，它包含一个对象。<code>auth</code>对象应该具有<code>authenticated</code>的属性，该属性的值应该为布尔值。
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testString: "assert((function() { const state = store.getState(); return typeof state.auth === 'object' && typeof state.auth.authenticated === 'boolean' && typeof state.count === 'number' })());"
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- text: <code>rootReducer</code>应该是一个合并了<code>counterReducer</code>和<code>authReducer</code>的函数。
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testString: getUserInput => assert((function() { const noWhiteSpace = getUserInput('index').replace(/\s/g,''); return typeof rootReducer === 'function' && noWhiteSpace.includes('Redux.combineReducers') })());
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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const INCREMENT = 'INCREMENT';
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const DECREMENT = 'DECREMENT';
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const counterReducer = (state = 0, action) => {
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switch(action.type) {
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case INCREMENT:
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return state + 1;
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case DECREMENT:
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return state - 1;
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default:
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return state;
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}
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};
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const LOGIN = 'LOGIN';
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const LOGOUT = 'LOGOUT';
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const authReducer = (state = {authenticated: false}, action) => {
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switch(action.type) {
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case LOGIN:
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return {
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authenticated: true
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}
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case LOGOUT:
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return {
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authenticated: false
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}
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default:
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return state;
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}
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};
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const rootReducer = // 在这里定义 root reducer
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const store = Redux.createStore(rootReducer);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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const INCREMENT = 'INCREMENT';
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const DECREMENT = 'DECREMENT';
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const counterReducer = (state = 0, action) => {
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switch(action.type) {
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case INCREMENT:
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return state + 1;
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case DECREMENT:
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return state - 1;
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default:
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return state;
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}
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};
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const LOGIN = 'LOGIN';
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const LOGOUT = 'LOGOUT';
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const authReducer = (state = {authenticated: false}, action) => {
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switch(action.type) {
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case LOGIN:
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return {
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authenticated: true
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}
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case LOGOUT:
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return {
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authenticated: false
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}
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default:
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return state;
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}
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};
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const rootReducer = Redux.combineReducers({
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count: counterReducer,
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auth: authReducer
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});
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const store = Redux.createStore(rootReducer);
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```
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</section>
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