264 lines
6.0 KiB
Markdown
264 lines
6.0 KiB
Markdown
---
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id: 5a24c314108439a4d4036144
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title: 使用 Provider 連接 Redux 和 React
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challengeType: 6
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forumTopicId: 301435
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dashedName: use-provider-to-connect-redux-to-react
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---
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# --description--
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在上一挑戰中，創建了 Redux store 和 action，分別用於處理消息數組和添加新消息。 下一步要爲 React 提供訪問 Redux store 及發起更新所需的 actions。 `react-redux` 包可幫助我們完成這些任務。
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React Redux 提供的 API 有兩個關鍵的功能：`Provider` 和 `connect`。 會在另一個挑戰會介紹 `connect`。 `Provider`是 React Redux 包裝 React 應用的 wrapper 組件， 它允許訪問整個組件樹中的 Redux `store` 及 `dispatch`（分發）方法。 `Provider` 需要兩個 props：Redux store 和 App 應用的子組件。 用於 App 組件的 `Provider` 可這樣定義：
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```jsx
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<Provider store={store}>
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<App/>
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</Provider>
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```
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# --instructions--
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此時，編輯器上顯示的是過去幾個挑戰中所有代碼， 包括 Redux store、actions、`DisplayMessages` 組件。 新出現的代碼是底部的`AppWrapper`組件， 這個頂級組件可用於渲染 `ReactRedux` 的 `Provider`，並把 Redux 的 store 作爲 props 傳入。 接着，渲染 `DisplayMessages` 爲子組件。 完成這些任務後，會看到 React 組件渲染到頁面上。
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**注意：** React Redux 在此可作全局變量，因此可通過點號表示法訪問 Provider。 利用這一點，編輯器上的代碼把 `Provider` 設置爲常量，便於你在 `AppWrapper` 渲染方法中使用。
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# --hints--
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`AppWrapper` 應渲染。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
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return mockedComponent.find('AppWrapper').length === 1;
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})()
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);
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```
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`Provider` 組件應傳入相當於 Redux store 的 `store` 參數。
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```js
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(getUserInput) =>
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
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return __helpers
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.removeWhiteSpace(getUserInput('index'))
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.includes('<Providerstore={store}>');
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})()
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);
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```
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`DisplayMessages` 應渲染爲 `AppWrapper` 的子組件。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
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return (
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mockedComponent.find('AppWrapper').find('DisplayMessages').length === 1
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);
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})()
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);
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```
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`DisplayMessages` 組件應渲染 `h2`、`input`、`button`、`ul` 四個元素。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(AppWrapper));
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return (
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mockedComponent.find('div').length === 1 &&
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mockedComponent.find('h2').length === 1 &&
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mockedComponent.find('button').length === 1 &&
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mockedComponent.find('ul').length === 1
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);
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})()
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);
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```
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# --seed--
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## --after-user-code--
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```jsx
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ReactDOM.render(<AppWrapper />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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// Redux:
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const ADD = 'ADD';
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const addMessage = (message) => {
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return {
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type: ADD,
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message
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}
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};
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const messageReducer = (state = [], action) => {
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switch (action.type) {
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case ADD:
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return [
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...state,
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action.message
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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 store = Redux.createStore(messageReducer);
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// React:
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class DisplayMessages extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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input: '',
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messages: []
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}
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this.handleChange = this.handleChange.bind(this);
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this.submitMessage = this.submitMessage.bind(this);
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}
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handleChange(event) {
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this.setState({
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input: event.target.value
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});
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}
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submitMessage() {
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this.setState((state) => {
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const currentMessage = state.input;
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return {
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input: '',
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messages: state.messages.concat(currentMessage)
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};
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});
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}
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render() {
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return (
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<div>
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<h2>Type in a new Message:</h2>
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<input
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value={this.state.input}
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onChange={this.handleChange}/><br/>
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<button onClick={this.submitMessage}>Submit</button>
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<ul>
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{this.state.messages.map( (message, idx) => {
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return (
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<li key={idx}>{message}</li>
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)
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})
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}
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</ul>
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</div>
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);
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}
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};
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const Provider = ReactRedux.Provider;
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class AppWrapper extends React.Component {
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// Render the Provider below this line
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// Change code above this line
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};
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```
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# --solutions--
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```jsx
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// Redux:
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const ADD = 'ADD';
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const addMessage = (message) => {
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return {
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type: ADD,
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message
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}
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};
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const messageReducer = (state = [], action) => {
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switch (action.type) {
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case ADD:
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return [
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...state,
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action.message
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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 store = Redux.createStore(messageReducer);
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// React:
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class DisplayMessages extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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input: '',
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messages: []
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}
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this.handleChange = this.handleChange.bind(this);
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this.submitMessage = this.submitMessage.bind(this);
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}
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handleChange(event) {
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this.setState({
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input: event.target.value
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});
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}
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submitMessage() {
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this.setState((state) => {
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const currentMessage = state.input;
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return {
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input: '',
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messages: state.messages.concat(currentMessage)
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};
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});
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}
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render() {
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return (
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<div>
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<h2>Type in a new Message:</h2>
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<input
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value={this.state.input}
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onChange={this.handleChange}/><br/>
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<button onClick={this.submitMessage}>Submit</button>
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<ul>
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{this.state.messages.map( (message, idx) => {
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return (
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<li key={idx}>{message}</li>
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)
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})
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}
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</ul>
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</div>
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);
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}
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};
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const Provider = ReactRedux.Provider;
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class AppWrapper extends React.Component {
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// Change code below this line
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render() {
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return (
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<Provider store = {store}>
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<DisplayMessages/>
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</Provider>
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);
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}
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// Change code above this line
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};
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```
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