https://developers.weixin.qq.com/miniprogram/dev/component/picker-view.html

直接用示例代码里面的在开发者工具中预览效果 后提示

VM32:1 ./index/index.wxml

 Now you can provide attr `wx:key` for a `wx:for` to improve performance.

  3 |   <picker-view indicator-style="height: 50px;" style="width: 100%; height: 300px;" value="{{value}}" bindchange="bindChange">

  4 |     <picker-view-column>

> 5 |       <view wx:for="{{years}}" style="line-height: 50px">{{item}}年</view>

    |        ^

  6 |     </picker-view-column>

  7 |     <picker-view-column>

  8 |       <view wx:for="{{months}}" style="line-height: 50px">{{item}}月</view>

如果复制样例中带有wx:key的代码则提示

VM54:1 ./index/index.wxml

 wx:key="{{days}}" does not look like a valid key name (did you mean wx:key="days" ?)

  10 |       </picker-view-column>

  11 |       <picker-view-column>

> 12 |         <view wx:for="{{days}}" wx:key="{{days}}" style="line-height: 50px; text-align: center;">{{item}}日</view>

     |          ^

  13 |       </picker-view-column>

  14 |       <picker-view-column>

  15 |         <view class="icon-container">