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

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5a24c314108439a4d4036149	將局部狀態提取到 Redux 中	6	301428	extract-local-state-into-redux

--description--

馬上就完成了! 請回顧一下爲管理 React messages app 的狀態寫的 Redux 代碼。 現在有了連接好的 Redux，還要從Presentational組件中提取狀態管理到 Redux， 目前，已連接 Redux，但正在 Presentational 組件中本地處理狀態。

--instructions--

在 Presentational 組件中，先刪除本地 state 中的 messages 屬性， 被刪的 messages 將由 Redux 管理。 接着，修改 submitMessage() 方法，使該方法從 this.props 那裏分發 submitNewMessage()；從本地 state 中傳入當前消息輸入作爲參數。 因本地狀態刪除了 messages 屬性，所以在調用 this.setState() 時也要刪除 messages 屬性。 最後，修改 render() 方法，使其所映射的消息是從 props 接收的，而不是 state

完成這些更改後，我們的應用會實現 Redux 管理應用的狀態，但它繼續運行着相同的功能。 此示例還闡明瞭組件獲得本地 state 的方式，即在自己的 state 中繼續跟蹤用戶本地輸入。 由此可見，Redux 爲 React 提供了很有用的狀態管理框架。 先前，僅使用 React 的本地狀態也實現了相同的結果，這在應付簡單的應用時通常是可行的。 但是，隨着應用變得越來越大，越來越複雜，應用的狀態管理也變得非常困難，Redux 就是爲解決這樣的問題而誕生的。

--hints--

AppWrapper 應該渲染該到頁面上。

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

Presentational 應該渲染到頁面上.

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

Presentational 組件應渲染 h2、input、button、ul 四個元素。

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 組件應接收 Redux store 的 messages 屬性。

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

Presentational 組件應接收創建 action 的函數的 submitMessage 屬性。

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

Presentational 組件的狀態應包含一個初始化爲空字符串的 input 屬性。

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
    );
  })()
);

鍵入 input 元素應更新 Presentational 組件的狀態。

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 組件上 dispatch submitMessage 應更新 Redux store 並清除本地狀態中的輸入。

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 組件應渲染 Redux store 中的 messages。

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
  );
};

--seed--

--after-user-code--

ReactDOM.render(<AppWrapper />, document.getElementById('root'))

--seed-contents--

// Redux:
const ADD = 'ADD';

const addMessage = (message) => {
  return {
    type: ADD,
    message: message
  }
};

const messageReducer = (state = [], action) => {
  switch (action.type) {
    case ADD:
      return [
        ...state,
        action.message
      ];
    default:
      return state;
  }
};

const store = Redux.createStore(messageReducer);

// React:
const Provider = ReactRedux.Provider;
const connect = ReactRedux.connect;

// Change code below this line
class Presentational extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: '',
      messages: []
    }
    this.handleChange = this.handleChange.bind(this);
    this.submitMessage = this.submitMessage.bind(this);
  }
  handleChange(event) {
    this.setState({
      input: event.target.value
    });
  }
  submitMessage() {
    this.setState((state) => ({
      input: '',
      messages: state.messages.concat(state.input)
    }));
  }
  render() {
    return (
      <div>
        <h2>Type in a new Message:</h2>
        <input
          value={this.state.input}
          onChange={this.handleChange}/><br/>
        <button onClick={this.submitMessage}>Submit</button>
        <ul>
          {this.state.messages.map( (message, idx) => {
              return (
                 <li key={idx}>{message}</li>
              )
            })
          }
        </ul>
      </div>
    );
  }
};
// Change code above this line

const mapStateToProps = (state) => {
  return {messages: state}
};

const mapDispatchToProps = (dispatch) => {
  return {
    submitNewMessage: (message) => {
      dispatch(addMessage(message))
    }
  }
};

const Container = connect(mapStateToProps, mapDispatchToProps)(Presentational);

class AppWrapper extends React.Component {
  render() {
    return (
      <Provider store={store}>
        <Container/>
      </Provider>
    );
  }
};

--solutions--

// Redux:
const ADD = 'ADD';

const addMessage = (message) => {
  return {
    type: ADD,
    message: message
  }
};

const messageReducer = (state = [], action) => {
  switch (action.type) {
    case ADD:
      return [
        ...state,
        action.message
      ];
    default:
      return state;
  }
};

const store = Redux.createStore(messageReducer);

// React:
const Provider = ReactRedux.Provider;
const connect = ReactRedux.connect;

// Change code below this line
class Presentational extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: ''
    }
 this.handleChange = this.handleChange.bind(this);
 this.submitMessage = this.submitMessage.bind(this);
  }
  handleChange(event) {
    this.setState({
      input: event.target.value
    });
  }
  submitMessage() {
    this.props.submitNewMessage(this.state.input);
    this.setState({
      input: ''
    });
  }
  render() {
    return (
      <div>
        <h2>Type in a new Message:</h2>
        <input
          value={this.state.input}
          onChange={this.handleChange}/><br/>
        <button onClick={this.submitMessage}>Submit</button>
        <ul>
          {this.props.messages.map( (message, idx) => {
              return (
                 <li key={idx}>{message}</li>
              )
            })
          }
        </ul>
      </div>
    );
  }
};
// Change code above this line

const mapStateToProps = (state) => {
  return {messages: state}
};

const mapDispatchToProps = (dispatch) => {
  return {
    submitNewMessage: (message) => {
      dispatch(addMessage(message))
    }
  }
};

const Container = connect(mapStateToProps, mapDispatchToProps)(Presentational);

class AppWrapper extends React.Component {
  render() {
    return (
      <Provider store={store}>
        <Container/>
      </Provider>
    );
  }
};