Controlled Components
Uncontrolled Components

Controlled Component

将React组件的state与表单的状态绑定，使state成为表单状态值的“唯一可信来源”，只能通过组件的setState()方法修改，如下：

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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('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }
  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

Uncontrolled Components

与Controlled Component不同，Uncontrolled Component使用ref属性，获取原生DOM引用，再操作DOM上的值。例如：

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class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.handleSubmit = this.handleSubmit.bind(this);
  }
  handleSubmit(event) {
    alert('A name was submitted: ' + this.input.value);
    event.preventDefault();
  }
  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" ref={(input) => this.input = input} />
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

默认值

React组件中，设置表单value属性值会覆盖DOM的value值（无法更改，除非用Controlled Components修改绑定的state），因此不能使用value属性，需使用defaultValue属性，如下

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render() {
  return (
    <form onSubmit={this.handleSubmit}>
      <label>
        Name:
        <input
          defaultValue="Bob"
          type="text"
          ref={(input) => this.input = input} />
      </label>
      <input type="submit" value="Submit" />
    </form>
  );
}

checkbox和radio使用defaultChecked，select使用defaultValue。