React的受控组件用法详解！

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>
        );
    }
}

// file类型的input，属性value是只读的，所以是非受控组件
<input type="file" />

// 多个input时，设置下name属性，即可动态操作，无需硬编码
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>
        );
    }
}

class EssayForm extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            value: '请撰写一篇关于你喜欢的 DOM 元素的文章.'
        };

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

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

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

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

// HTML中使用selected属性
< select >
  <option value="grapefruit">葡萄柚</option>
  <option value="lime">酸橙</option>
  <option selected value="coconut">椰子</option>
  <option value="mango">芒果</option>
</select >

// React中使用value属性
class FlavorForm extends React.Component {
    constructor(props) {
        super(props);
        this.state = { value: 'coconut' };

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

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

    handleSubmit(event) {
        alert('你喜欢的风味是: ' + this.state.value);
        event.preventDefault();
    }

    render() {
        return (
            <form onSubmit={this.handleSubmit}>
                <label>
                    选择你喜欢的风味:
                    <select value={this.state.value} onChange={this.handleChange}>
                        <option value="grapefruit">葡萄柚</option>
                        <option value="lime">酸橙</option>
                        <option value="coconut">椰子</option>
                        <option value="mango">芒果</option>
                    </select>
                </label>
                <input type="submit" value="提交" />
            </form>
        );
    }
}

// 传递数组给value属性，表示select标签，选中多个选项
<select multiple={true} value={['B', 'C']}>