freeCodeCamp/curriculum/challenges/chinese/03-front-end-libraries/react-and-redux/extract-local-state-into-redux.md

---
id: 5a24c314108439a4d4036149
title: 将局部状态提取到 Redux 中
challengeType: 6
forumTopicId: 301428
---

# --description--

胜利就在眼前了！请回顾一下为管理 React messages app 的状态写的 Redux 代码。现在有了连接好的 Redux，你还要从`Presentational`组件中提取状态管理到 Redux，在`Presentational`组件内处理本地状态。

# --instructions--

在`Presentational`组件中，先删除本地`state`中的`messages`属性，被删的 messages 将由 Redux 管理。接着，修改`submitMessage()`方法，使该方法从`this.props`那里分发`submitNewMessage()`；从本地`state`中传入当前消息输入作为参数。因本地状态删除了`messages`属性，所以在调用`this.setState()`时也要删除该属性。最后，修改`render()`方法，使其所映射的消息是从`props`接收的，而不是`state`

完成这些更改后，我们的应用会实现 Redux 管理应用的状态，但它继续运行着相同的功能。此示例还阐明了组件获得本地状态的方式，即在自己的状态中继续跟踪用户本地输入。由此可见，Redux 为 React 提供了很有用的状态管理框架。先前，你仅使用 React 的本地状态也实现了相同的结果，这在应付简单的应用时通常是可行的。但是，随着应用变得越来越大，越来越复杂，应用的状态管理也变得非常困难，Redux 就是为解决这样的问题而诞生的。

# --hints--

`AppWrapper`应该渲染该到页面。

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    return mockedComponent.find('AppWrapper').length === 1;
  })()
);
```

`Presentational` 应该渲染到页面上.

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    return mockedComponent.find('Presentational').length === 1;
  })()
);
```

`Presentational`组件应渲染`h2`、`input`、`button`、`ul`四个元素。

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    const PresentationalComponent = mockedComponent.find('Presentational');
    return (
      PresentationalComponent.find('div').length === 1 &&
      PresentationalComponent.find('h2').length === 1 &&
      PresentationalComponent.find('button').length === 1 &&
      PresentationalComponent.find('ul').length === 1
    );
  })()
);
```

`Presentational`组件应接收 Redux store 的`消息`属性。

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    const PresentationalComponent = mockedComponent.find('Presentational');
    const props = PresentationalComponent.props();
    return Array.isArray(props.messages);
  })()
);
```

`Presentational`组件应接收创建 action 的函数`submitMessage`属性。

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    const PresentationalComponent = mockedComponent.find('Presentational');
    const props = PresentationalComponent.props();
    return typeof props.submitNewMessage === 'function';
  })()
);
```

`Presentational`组件的状态应包含一个初始化为空字符串的input属性。

```js
assert(
  (function () {
    const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
    const PresentationalState = mockedComponent
      .find('Presentational')
      .instance().state;
    return (
      typeof PresentationalState.input === 'string' &&
      Object.keys(PresentationalState).length === 1
    );
  })()
);
```

键入`input`元素应更新`Presentational`组件的状态。

```js
async () => {
  const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
  const testValue = '__MOCK__INPUT__';
  const waitForIt = (fn) =>
    new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
  const causeChange = (c, v) =>
    c.find('input').simulate('change', { target: { value: v } });
  let initialInput = mockedComponent.find('Presentational').find('input');
  const changed = () => {
    causeChange(mockedComponent, testValue);
    return waitForIt(() => mockedComponent);
  };
  const updated = await changed();
  const updatedInput = updated.find('Presentational').find('input');
  assert(
    initialInput.props().value === '' &&
      updatedInput.props().value === '__MOCK__INPUT__'
  );
};
```

在`Presentational`组件上 dispatch `submitMessage`应更新 Redux store 并清除本地状态中的输入。

```js
async () => {
  const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
  const waitForIt = (fn) =>
    new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
  let beforeProps = mockedComponent.find('Presentational').props();
  const testValue = '__TEST__EVENT__INPUT__';
  const causeChange = (c, v) =>
    c.find('input').simulate('change', { target: { value: v } });
  const changed = () => {
    causeChange(mockedComponent, testValue);
    return waitForIt(() => mockedComponent);
  };
  const clickButton = () => {
    mockedComponent.find('button').simulate('click');
    return waitForIt(() => mockedComponent);
  };
  const afterChange = await changed();
  const afterChangeInput = afterChange.find('input').props().value;
  const afterClick = await clickButton();
  const afterProps = mockedComponent.find('Presentational').props();
  assert(
    beforeProps.messages.length === 0 &&
      afterChangeInput === testValue &&
      afterProps.messages.pop() === testValue &&
      afterClick.find('input').props().value === ''
  );
};
```

`Presentational`组件应渲染 Redux store 中的`messages`

```js
async () => {
  const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
  const waitForIt = (fn) =>
    new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
  let beforeProps = mockedComponent.find('Presentational').props();
  const testValue = '__TEST__EVENT__INPUT__';
  const causeChange = (c, v) =>
    c.find('input').simulate('change', { target: { value: v } });
  const changed = () => {
    causeChange(mockedComponent, testValue);
    return waitForIt(() => mockedComponent);
  };
  const clickButton = () => {
    mockedComponent.find('button').simulate('click');
    return waitForIt(() => mockedComponent);
  };
  const afterChange = await changed();
  const afterChangeInput = afterChange.find('input').props().value;
  const afterClick = await clickButton();
  const afterProps = mockedComponent.find('Presentational').props();
  assert(
    beforeProps.messages.length === 0 &&
      afterChangeInput === testValue &&
      afterProps.messages.pop() === testValue &&
      afterClick.find('input').props().value === '' &&
      afterClick.find('ul').childAt(0).text() === testValue
  );
};
```

# --solutions--