---
id: 5a24c314108439a4d4036142
title: 首先在本地管理状态
challengeType: 6
forumTopicId: 301431
dashedName: manage-state-locally-first
---
# --description--
这一关的任务是完成 `DisplayMessages` 组件的创建。
# --instructions--
首先，在 `render()` 方法中，让组件渲染 `input`、`button`、`ul` 三个元素。 `input` 元素的改变会触发 `handleChange()` 方法。 此外，`input` 元素会渲染组件状态中 `input` 的值。 点击按钮 `button` 需触发 `submitMessage()` 方法。
接着，写出这两种方法。 `handleChange()` 方法会更新 `input` 为用户正在输入的内容。 `submitMessage()` 方法把当前存储在 `input` 的消息与本地状态的 `messages` 数组连接起来，并清除 `input` 的值。
最后，在 `ul` 中展示 `messages` 数组，其中每个元素内容需放到 `li` 元素内。
# --hints--
`DisplayMessages` 组件的初始状态应是 `{ input: "", messages: [] }`。
```js
assert(
(function () {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const initialState = mockedComponent.state();
return (
typeof initialState === 'object' &&
initialState.input === '' &&
initialState.messages.length === 0
);
})()
);
```
`DisplayMessages` 组件应渲染含 `h2`、`button`、`ul`、`li` 四个子元素的`div`
```js
async () => {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const waitForIt = (fn) =>
new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
const state = () => {
mockedComponent.setState({ messages: ['__TEST__MESSAGE'] });
return waitForIt(() => mockedComponent);
};
const updated = await state();
assert(
updated.find('div').length === 1 &&
updated.find('h2').length === 1 &&
updated.find('button').length === 1 &&
updated.find('ul').length === 1 &&
updated.find('li').length > 0
);
};
```
`.map` 应该用于 `messages` 数组。
```js
assert(code.match(/this\.state\.messages\.map/g));
```
`input` 元素应渲染本地状态中的 `input` 值。
```js
async () => {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const waitForIt = (fn) =>
new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
const causeChange = (c, v) =>
c.find('input').simulate('change', { target: { value: v } });
const testValue = '__TEST__EVENT__INPUT';
const changed = () => {
causeChange(mockedComponent, testValue);
return waitForIt(() => mockedComponent);
};
const updated = await changed();
assert(updated.find('input').props().value === testValue);
};
```
调用 `handleChange` 方法时应更新状态中的 `input` 值为当前输入。
```js
async () => {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const waitForIt = (fn) =>
new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
const causeChange = (c, v) =>
c.find('input').simulate('change', { target: { value: v } });
const initialState = mockedComponent.state();
const testMessage = '__TEST__EVENT__MESSAGE__';
const changed = () => {
causeChange(mockedComponent, testMessage);
return waitForIt(() => mockedComponent);
};
const afterInput = await changed();
assert(
initialState.input === '' &&
afterInput.state().input === '__TEST__EVENT__MESSAGE__'
);
};
```
单击 `Add message` 按钮应调用 `submitMessage` 方法，添加当前 `input` 到状态中的 `messages` 数组。
```js
async () => {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const waitForIt = (fn) =>
new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
const causeChange = (c, v) =>
c.find('input').simulate('change', { target: { value: v } });
const initialState = mockedComponent.state();
const testMessage_1 = '__FIRST__MESSAGE__';
const firstChange = () => {
causeChange(mockedComponent, testMessage_1);
return waitForIt(() => mockedComponent);
};
const firstResult = await firstChange();
const firstSubmit = () => {
mockedComponent.find('button').simulate('click');
return waitForIt(() => mockedComponent);
};
const afterSubmit_1 = await firstSubmit();
const submitState_1 = afterSubmit_1.state();
const testMessage_2 = '__SECOND__MESSAGE__';
const secondChange = () => {
causeChange(mockedComponent, testMessage_2);
return waitForIt(() => mockedComponent);
};
const secondResult = await secondChange();
const secondSubmit = () => {
mockedComponent.find('button').simulate('click');
return waitForIt(() => mockedComponent);
};
const afterSubmit_2 = await secondSubmit();
const submitState_2 = afterSubmit_2.state();
assert(
initialState.messages.length === 0 &&
submitState_1.messages.length === 1 &&
submitState_2.messages.length === 2 &&
submitState_2.messages[1] === testMessage_2
);
};
```
`submitMessage` 方法应清除当前输入。
```js
async () => {
const mockedComponent = Enzyme.mount(React.createElement(DisplayMessages));
const waitForIt = (fn) =>
new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 100));
const causeChange = (c, v) =>
c.find('input').simulate('change', { target: { value: v } });
const initialState = mockedComponent.state();
const testMessage = '__FIRST__MESSAGE__';
const firstChange = () => {
causeChange(mockedComponent, testMessage);
return waitForIt(() => mockedComponent);
};
const firstResult = await firstChange();
const firstState = firstResult.state();
const firstSubmit = () => {
mockedComponent.find('button').simulate('click');
return waitForIt(() => mockedComponent);
};
const afterSubmit = await firstSubmit();
const submitState = afterSubmit.state();
assert(firstState.input === testMessage && submitState.input === '');
};
```
# --seed--
## --after-user-code--
```jsx
ReactDOM.render(, document.getElementById('root'))
```
## --seed-contents--
```jsx
class DisplayMessages extends React.Component {
constructor(props) {
super(props);
this.state = {
input: '',
messages: []
}
}
// Add handleChange() and submitMessage() methods here
render() {
return (
Type in a new Message:
{ /* Render an input, button, and ul below this line */ }
{ /* Change code above this line */ }
);
}
};
```
# --solutions--
```jsx
class DisplayMessages 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) => {
const currentMessage = state.input;
return {
input: '',
messages: state.messages.concat(currentMessage)
};
});
}
render() {
return (
);
}
};
```