176 lines
5.0 KiB
Markdown
176 lines
5.0 KiB
Markdown
---
|
||
id: 5a24c314108439a4d4036154
|
||
title: 组合多个 Reduces
|
||
challengeType: 6
|
||
forumTopicId: 301436
|
||
dashedName: combine-multiple-reducers
|
||
---
|
||
|
||
# --description--
|
||
|
||
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 `createStore()`方法。
|
||
|
||
为了让我们将可以将多个 reducer 组合在一起，Redux 提供了`combineReducers()`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。
|
||
|
||
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`combineReducers()`方法，如下所示：
|
||
|
||
```js
|
||
const rootReducer = Redux.combineReducers({
|
||
auth: authenticationReducer,
|
||
notes: notesReducer
|
||
});
|
||
```
|
||
|
||
现在，`notes`键将包含与我们的注释相关联的所有状态，并由我们的`notesReducer`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`auth`和`notes`属性的简单对象。
|
||
|
||
# --instructions--
|
||
|
||
代码编辑器中提供了`counterReducer()`和`authReducer()`函数以及 Redux store。使用`Redux.combineReducers()`方法编写完成`rootReducer()`函数。将`counterReducer`分配给一个叫做`count`的键，将`authReducer`分配给一个叫做`auth`的键。
|
||
|
||
# --hints--
|
||
|
||
`counterReducer`应该递增和递减`state`。
|
||
|
||
```js
|
||
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;
|
||
})()
|
||
);
|
||
```
|
||
|
||
`authenticated`的`state`值应该在`true`和`false`之间切换。
|
||
|
||
```js
|
||
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;
|
||
})()
|
||
);
|
||
```
|
||
|
||
store `state`应该有两个 key：一个是`count`，它包含一个数字。另一个`auth`，它包含一个对象。`auth`对象应该具有`authenticated`的属性，该属性的值应该为布尔值。
|
||
|
||
```js
|
||
assert(
|
||
(function () {
|
||
const state = store.getState();
|
||
return (
|
||
typeof state.auth === 'object' &&
|
||
typeof state.auth.authenticated === 'boolean' &&
|
||
typeof state.count === 'number'
|
||
);
|
||
})()
|
||
);
|
||
```
|
||
|
||
`rootReducer`应该是一个合并了`counterReducer`和`authReducer`的函数。
|
||
|
||
```js
|
||
(getUserInput) =>
|
||
assert(
|
||
(function () {
|
||
const noWhiteSpace = getUserInput('index').replace(/\s/g, '');
|
||
return (
|
||
typeof rootReducer === 'function' &&
|
||
noWhiteSpace.includes('Redux.combineReducers')
|
||
);
|
||
})()
|
||
);
|
||
```
|
||
|
||
# --seed--
|
||
|
||
## --seed-contents--
|
||
|
||
```js
|
||
const INCREMENT = 'INCREMENT';
|
||
const DECREMENT = 'DECREMENT';
|
||
|
||
const counterReducer = (state = 0, action) => {
|
||
switch(action.type) {
|
||
case INCREMENT:
|
||
return state + 1;
|
||
case DECREMENT:
|
||
return state - 1;
|
||
default:
|
||
return state;
|
||
}
|
||
};
|
||
|
||
const LOGIN = 'LOGIN';
|
||
const LOGOUT = 'LOGOUT';
|
||
|
||
const authReducer = (state = {authenticated: false}, action) => {
|
||
switch(action.type) {
|
||
case LOGIN:
|
||
return {
|
||
authenticated: true
|
||
}
|
||
case LOGOUT:
|
||
return {
|
||
authenticated: false
|
||
}
|
||
default:
|
||
return state;
|
||
}
|
||
};
|
||
|
||
const rootReducer = // Define the root reducer here
|
||
|
||
const store = Redux.createStore(rootReducer);
|
||
```
|
||
|
||
# --solutions--
|
||
|
||
```js
|
||
const INCREMENT = 'INCREMENT';
|
||
const DECREMENT = 'DECREMENT';
|
||
|
||
const counterReducer = (state = 0, action) => {
|
||
switch(action.type) {
|
||
case INCREMENT:
|
||
return state + 1;
|
||
case DECREMENT:
|
||
return state - 1;
|
||
default:
|
||
return state;
|
||
}
|
||
};
|
||
|
||
const LOGIN = 'LOGIN';
|
||
const LOGOUT = 'LOGOUT';
|
||
|
||
const authReducer = (state = {authenticated: false}, action) => {
|
||
switch(action.type) {
|
||
case LOGIN:
|
||
return {
|
||
authenticated: true
|
||
}
|
||
case LOGOUT:
|
||
return {
|
||
authenticated: false
|
||
}
|
||
default:
|
||
return state;
|
||
}
|
||
};
|
||
|
||
const rootReducer = Redux.combineReducers({
|
||
count: counterReducer,
|
||
auth: authReducer
|
||
});
|
||
|
||
const store = Redux.createStore(rootReducer);
|
||
```
|