[JavaScript知识库]react利用循环创建组件时，给key值很重要，react内部会对这个key值进行一个判断

React内部，key值不相同时，会重新创建组件

为FilterPicker 提供一个key值，React内部自然会对组件的key值进行一个判断，
当key值不同的时候     会删除改组件  重新创建改组件

  renderFilterPicker = () => {
    const {
      openType,
      filterData: { area, subway, rentType, price },
      selectedValue
    } = this.state;
    let data = [], cols =3, defaultValue =selectedValue[openType] ;
    if (openType !== "area" && openType !== "mode" && openType !== "price") {
      return null;
    }
    switch (openType) {
      case "area":
        data = [area, subway];
        cols = 3;
        break;
      case "mode":
        data = rentType;
        cols = 1;
        break;
      case "price":
        data = price;
        cols = 1;
        break;
      default:
        break;
    }
    return (
      <FilterPicker 
      key={openType}
      type={openType} 
      onCancel={this.onCancel} 
      onSave={this.onSave} 
      data={data} 
      cols={cols}
      defaultValue={defaultValue} />
    );
  };