使用React Motion的TransitionMotion，我想对1个或更多盒子进行动画制作。当一个框进入视图时，其宽度和高度应从0像素变为200像素，其不透明度应从0变为1。当该框离开视图时，应该发生相反的情况（宽度/高度=
0，不透明度= 0 ）

我已经尝试在这里http://codepen.io/danijel/pen/Rabo​​xO解决此问题，但是我的代码无法正确转换该框。框的样式立即跳到200像素的宽度/高度，而不是过渡到其中。

代码有什么问题？

let Motion = ReactMotion.Motion
let TransitionMotion = ReactMotion.TransitionMotion
let spring = ReactMotion.spring
let presets = ReactMotion.presets

const Demo = React.createClass({
  getInitialState() {
    return {
      items: []
    }
  },
  componentDidMount() {

    let ctr = 0

    setInterval(() => {
      ctr++
      console.log(ctr)
      if (ctr % 2 == 0) {
        this.setState({
          items: [{key: 'b', width: 200, height: 200, opacity: 1}], // fade box in
        });
      } else {
        this.setState({
          items: [], // fade box out
        });
      }

    }, 1000)
  },
  willLeave() {
    // triggered when c's gone. Keeping c until its width/height reach 0.
    return {width: spring(0), height: spring(0), opacity: spring(0)};
  },

  willEnter() {
    return {width: 0, height: 0, opacity: 1};
  },

  render() {
    return (
      <TransitionMotion
        willEnter={this.willEnter}
        willLeave={this.willLeave}
        defaultStyles={this.state.items.map(item => ({
          key: item.key,
          style: {
            width: 0, 
            height: 0,
            opacity: 0
          },
        }))}
        styles={this.state.items.map(item => ({
          key: item.key,
          style: {
            width: item.width, 
            height: item.height,
            opacity: item.opacity
          },
        }))}
        >
        {interpolatedStyles =>
          <div>
            {interpolatedStyles.map(config => {
              return <div key={config.key} style={{...config.style, backgroundColor: 'yellow'}}>
                <div className="label">{config.style.width}</div>
              </div>
            })}
          </div>
        }
      </TransitionMotion>
    );
  },
});

ReactDOM.render(<Demo />, document.getElementById('app'));