How to get selected value of a dropdown menu in Re

问题:

I'm using react and I want to get the value of the selected option of a dropdown in react but I don't know how. Any suggestions? thanks! My dropdown is just a select like:

            <select id = "dropdown">
                <option value="N/A">N/A</option>
                <option value="1">1</option>
                <option value="2">2</option>
                <option value="3">3</option>
                <option value="4">4</option>
            </select>

回答1:

The code in the render method represents the component at any given time. If you do something like this, the user won't be able to make selections using the form control:

<select value="Radish">
  <option value="Orange">Orange</option>
  <option value="Radish">Radish</option>
  <option value="Cherry">Cherry</option>
</select>

So there are two solutions for working with forms controls:

1. Controlled Components Use component state to reflect the user's selections. This provides the most control, since any changes you make to state will be reflected in the component's rendering:

example:

var FruitSelector = React.createClass({
    getInitialState:function(){
      return {selectValue:'Radish'};
  },
    handleChange:function(e){
    this.setState({selectValue:e.target.value});
  },
  render: function() {
    var message='You selected '+this.state.selectValue;
    return (
      <div>
      <select 
        value={this.state.selectValue} 
        onChange={this.handleChange} 
      >
       <option value="Orange">Orange</option>
        <option value="Radish">Radish</option>
        <option value="Cherry">Cherry</option>
      </select>
      <p>{message}</p>
      </div>        
    );
  }
});

React.render(<FruitSelector name="World" />, document.body);

JSFiddle: http://jsfiddle.net/xe5ypghv/

2. Uncontrolled Components The other option is to not control the value and simply respond to onChange events. In this case you can use the defaultValue prop to set an initial value.

   <div>
    <select defaultValue={this.state.selectValue} 
    onChange={this.handleChange} 
    >
       <option value="Orange">Orange</option>
       <option value="Radish">Radish</option>
       <option value="Cherry">Cherry</option>
     </select>
     <p>{message}</p>
     </div>       
   

http://jsfiddle.net/kb3gN/10396/

The docs for this are great: http://facebook.github.io/react/docs/forms.html and also show how to work with multiple selections.

UPDATE

A variant of Option 1 (using a controlled component) is to use Redux and React-Redux to create a container component. This involves connect and a mapStateToProps function, which is easier than it sounds but probably overkill if you're just starting out.

回答2:

Implement your Dropdown as

<select id = "dropdown" ref = {(input)=> this.menu = input}>
    <option value="N/A">N/A</option>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
</select>

Now, to obtain the selected option value of the dropdown menu just use:

let res = this.menu.value;

回答3:

Just use onChange event of the <select> object. Selected value is in e.target.value then.

By the way, it's a bad practice to use id="...". It's better to use ref=">.." http://facebook.github.io/react/docs/more-about-refs.html