列表和Key

在js中转换列表通过map的方式

const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map((number) => number * 2);
console.log(doubled);

在React中渲染多个组件也可以使用map

const numbers = [1, 2, 3, 4, 5];
const listItems = numbers.map((number) =>
  <li>{number}</li>
);

ReactDOM.render(
  <ul>{listItems}</ul>,
  document.getElementById('root')
);

但是通常是需要将一个列表中数据渲染到组件中

function NumberList(props) {
  const numbers = props.numbers;
  const listItems = numbers.map((number) =>
    <li key={number.toString()}>
      {number}
    </li>
  );
  return (
    <ul>{listItems}</ul>
  );
}

const numbers = [1, 2, 3, 4, 5];
ReactDOM.render(
  <NumberList numbers={numbers} />,
  document.getElementById('root')
);

这里的key帮助React识别哪些元素改变了，比如被添加或删除。因此你应当给数组中的每一个元素赋予独一无二的标识，一般为数据的id，例如

const todoItems = todos.map((todo) =>
  <li key={todo.id}>
    {todo.text}
  </li>
);

或者是使用元素索引

const todoItems = todos.map((todo, index) =>
  <li key={index}>
    {todo.text}
  </li>
);

如需要拆分为组件的话

function ListItem(props) {
  // 正确！这里不需要指定 key：
  return <li>{props.value}</li>;
}

function NumberList(props) {
  const numbers = props.numbers;
  const listItems = numbers.map((number) =>
    // 正确！key 应该在数组的上下文中被指定
    <ListItem key={number.toString()} value={number} />
  );
  return (
    <ul>
      {listItems}
    </ul>
  );
}

const numbers = [1, 2, 3, 4, 5];
ReactDOM.render(
  <NumberList numbers={numbers} />,
  document.getElementById('root')
);

如果是多个组件的话

function Blog(props) {
  const sidebar = (
    <ul>
      {props.posts.map((post) =>
        <li key={post.id}>
          {post.title}
        </li>
      )}
    </ul>
  );
  const content = props.posts.map((post) =>
    <div key={post.id}>
      <h3>{post.title}</h3>
      <p>{post.content}</p>
    </div>
  );
  return (
    <div>
      {sidebar}
      <hr />
      {content}
    </div>
  );
}

const posts = [
  {id: 1, title: 'Hello World', content: 'Welcome to learning React!'},
  {id: 2, title: 'Installation', content: 'You can install React from npm.'}
];
ReactDOM.render(
  <Blog posts={posts} />,
  document.getElementById('root')
);

如果要在组件中使用，需要显示传递

const content = posts.map((post) =>
  <Post
    key={post.id}
    id={post.id}
    title={post.title} />
);

也可以在JSX中嵌入map

function NumberList(props) {
  const numbers = props.numbers;
  const listItems = numbers.map((number) =>
    <ListItem key={number.toString()}
              value={number} />
  );
  return (
    <ul>
      {listItems}
    </ul>
  );
}

写成

function NumberList(props) {
  const numbers = props.numbers;
  return (
    <ul>
      {numbers.map((number) =>
        <ListItem key={number.toString()}
                  value={number} />
      )}
    </ul>
  );
}

表单

受控组件

表单中的元素，例如<input>、<textarea>和<select>通常需要维护state，并根据用户输入进行更新，放到React中，使用react的state作为唯一数据源，通过setState()进行更新

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: ''};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    alert('提交的名字: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          名字:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </label>
        <input type="submit" value="提交" />
      </form>
    );
  }
}

对于select标签，在React中不能使用selected属性，也是需要单独更新的，针对多选

<select multiple={true} value={['B', 'C']}>

处理多个输入

当有多个输入的时候，需要对每个输入指定一个name

class Reservation extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      isGoing: true,
      numberOfGuests: 2
    };

    this.handleInputChange = this.handleInputChange.bind(this);
  }

  handleInputChange(event) {
    const target = event.target;
    const value = target.type === 'checkbox' ? target.checked : target.value;
    const name = target.name;

    this.setState({
      [name]: value
    });
  }

  render() {
    return (
      <form>
        <label>
          参与:
          <input
            name="isGoing"
            type="checkbox"
            checked={this.state.isGoing}
            onChange={this.handleInputChange} />
        </label>
        <br />
        <label>
          来宾人数:
          <input
            name="numberOfGuests"
            type="number"
            value={this.state.numberOfGuests}
            onChange={this.handleInputChange} />
        </label>
      </form>
    );
  }
}

需要注意的是es6的语法，用来更新对应数据

this.setState({
  [name]: value
});

等价于es5的

var partialState = {};
partialState[name] = value;
this.setState(partialState);

子组件传递数据到父组件

正常一个组件的时候

class HelloMessage extends React.Component {
  constructor(props) {
      super(props);
      this.state = {value: 'Hello Runoob!'};
      this.handleChange = this.handleChange.bind(this);
  }

  handleChange(event) {
    this.setState({value: '菜鸟教程'})
  }
  render() {
    var value = this.state.value;
    return <div>
            <button onClick={this.handleChange}>点我</button>
            <h4>{value}</h4>
           </div>;
  }
}
ReactDOM.render(
  <HelloMessage />,
  document.getElementById('example')
);

子组件将事件传递

class Content extends React.Component {
  render() {
    return  <div>
              <button onClick = {this.props.updateStateProp}>点我</button>
              <h4>{this.props.myDataProp}</h4>
           </div>
  }
}
class HelloMessage extends React.Component {
  constructor(props) {
      super(props);
      this.state = {value: 'Hello Runoob!'};
      this.handleChange = this.handleChange.bind(this);
  }
  handleChange(event) {
    this.setState({value: '菜鸟教程'})
  }
  render() {
    var value = this.state.value;
    return <div>
            <Content myDataProp = {value} 
              updateStateProp = {this.handleChange}></Content>
           </div>;
  }
}
ReactDOM.render(
  <HelloMessage />,
  document.getElementById('example')
);

状态提升

const scaleNames = {
  c: 'Celsius',
  f: 'Fahrenheit'
};

function toCelsius(fahrenheit) {
  return (fahrenheit - 32) * 5 / 9;
}

function toFahrenheit(celsius) {
  return (celsius * 9 / 5) + 32;
}

function tryConvert(temperature, convert) {
  const input = parseFloat(temperature);
  if (Number.isNaN(input)) {
    return '';
  }
  const output = convert(input);
  const rounded = Math.round(output * 1000) / 1000;
  return rounded.toString();
}

function BoilingVerdict(props) {
  if (props.celsius >= 100) {
    return <p>The water would boil.</p>;
  }
  return <p>The water would not boil.</p>;
}

class TemperatureInput extends React.Component {
  constructor(props) {
    super(props);
    this.handleChange = this.handleChange.bind(this);
  }

  handleChange(e) {
    this.props.onTemperatureChange(e.target.value);
  }

  render() {
    const temperature = this.props.temperature;
    const scale = this.props.scale;
    return (
      <fieldset>
        <legend>Enter temperature in {scaleNames[scale]}:</legend>
        <input value={temperature}
               onChange={this.handleChange} />
      </fieldset>
    );
  }
}

class Calculator extends React.Component {
  constructor(props) {
    super(props);
    this.handleCelsiusChange = this.handleCelsiusChange.bind(this);
    this.handleFahrenheitChange = this.handleFahrenheitChange.bind(this);
    this.state = {temperature: '', scale: 'c'};
  }

  handleCelsiusChange(temperature) {
    this.setState({scale: 'c', temperature});
  }

  handleFahrenheitChange(temperature) {
    this.setState({scale: 'f', temperature});
  }

  render() {
    const scale = this.state.scale;
    const temperature = this.state.temperature;
    const celsius = scale === 'f' ? tryConvert(temperature, toCelsius) : temperature;
    const fahrenheit = scale === 'c' ? tryConvert(temperature, toFahrenheit) : temperature;

    return (
      <div>
        <TemperatureInput
          scale="c"
          temperature={celsius}
          onTemperatureChange={this.handleCelsiusChange} />
        <TemperatureInput
          scale="f"
          temperature={fahrenheit}
          onTemperatureChange={this.handleFahrenheitChange} />
        <BoilingVerdict
          celsius={parseFloat(celsius)} />
      </div>
    );
  }
}

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