将CSS过渡添加到越来越多的项目列表中

Question

我有一个组件，该组件以空的项目/框列表开始，并且随着列表的增加，先前的项目在que中被下推。您可以查看以下代码段作为示例。如何添加CSS过渡，以便您可以直观地看到项目从其先前位置向下移动到下一位置？谢谢！

class App extends React.Component {
    constructor() {
    super();
    this.state = {
      count: 0
    };
    this.handleClick = this.handleClick.bind(this);
    this.getItems = this.getItems.bind(this);
  }

  handleClick() {
    this.setState({
      count: this.state.count + 1,
    });
  }
  
  getItems() {
    let items = [];
    for (let j = 0; j < this.state.count; j++) {
      items.push(<div className="item">This is a box {j}</div>)
    }
    return items.reverse();
  };

  render() {
    return (
      <div className="container">
        <button onClick={this.handleClick}>Add box</button>
        {this.getItems()}
      </div>
    );
  }
}



ReactDOM.render(<App />, app);

.container {
  border: 1px solid green !important;
}


.item {
  height: 40px;
  width: 100px;
  background: yellow;
  border: 2px solid red;
  margin: 20px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="app"></div>

Answer 1

您可以在最大高度上使用动画； 但是您必须知道.item的大小，max-height：100％在动画上不起作用。

class App extends React.Component {
    constructor() {
    super();
    this.state = {
      count: 0
    };
    this.handleClick = this.handleClick.bind(this);
    this.getItems = this.getItems.bind(this);
  }

  handleClick() {
    this.setState({
      count: this.state.count + 1,
    });
  }
  
  getItems() {
    let items = [];
    for (let j = 0; j < this.state.count; j++) {
      items.push(<div className="item">This is a box {j}</div>)
    }
    return items.reverse();
  };

  render() {
    return (
      <div className="container">
        <button onClick={this.handleClick}>Add box</button>
        {this.getItems()}
      </div>
    );
  }
}



ReactDOM.render(<App />, app);

.container {
  border: 1px solid green !important;
}


.item {
  height: 40px;
  width: 100px;
  background: yellow;
  border: 2px solid red;
  margin: 20px;

  animation-name: example;
  animation-duration: 2s;
  animation-iteration-count: 1;
  overflow: hidden;
}
@keyframes example {
  from { max-height: 0px;}
  to { max-height: 40px;}
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="app"></div>