Example of method to implement WeChat applet drop-down menu (with animation)

You can copy and use it directly. This is just a shell. You can fill it with your own content.

Add filter items in pick-header , add the filtered option content in pick-container, and display the real content in content. The height of
content will be dynamically calculated in js based on the current mobile phone resolution. The height value is contentHeight, so it can be nested inside. A scroll-view, set the height to contentHeight to achieve content sliding.

Okay, no more nonsense, just look at the picture and the code.

Drop-down menu example.gif

wxml

<view class="content-container">
  <view class="pick-header" bindtap="onPickHeaderClick">
    筛选pick-header view z-index:60
  </view>

  <view class="pick-container {{needAnimation ? (openPicker ? &#39;slidown&#39; : &#39;slidup&#39;) : &#39;&#39;}}" >
    筛选项 pick-container view z-index:50
  </view>

  <view class="shadow" style="height:{{contentHeight}}px;line-height:{{contentHeight}}px" hidden="  {{!openPicker}}">我是半透明阴影遮罩 view shadow  z-index:40</view>

  <view class="content" style="height:{{contentHeight}}px">
    我是内容content view z-index:20
  </view>
</view>

wxss

/*根布局*/
.content-container {
width: 100%;
position: absolute;
}

/*筛选头部*/
.pick-header {
  width: 100%;
  height: 72rpx;
  z-index: 60;
  position: fixed;
 background-color: lightcoral;
}

/*筛选项容器布局*/
.pick-container {
  width: 100%;
  height: 300rpx;
  background-color: lightgoldenrodyellow;
  position: absolute;
  z-index: 50;
  top: -228rpx;
}

/*筛选项隐藏 显示动画 start*/
@keyframes slidown {
  from {
    transform: translateY(0%);
  }

  to {
    transform: translateY(100%);
  }
}

.slidown {
  display: block;
  animation: slidown 0.1s ease-in both;
}

@keyframes slidup {
  from {
    transform: translateY(100%);
  }

  to {
    transform: translateY(0%);
  }
}

.slidup {
  display: block;
  animation: slidup 0.2s ease-in both;
}
/*筛选项隐藏 显示动画 end*/

/*筛选项显示出来的时候的阴影*/
.shadow {
  width: 100%;
  background-color: rgba(1, 1, 1, 0.2);
  position: absolute;
  z-index: 40;
  top: 72rpx;
}

/*内容容器布局*/
.content {
  width: 100%;
  position: absolute;
  top: 72rpx;
  z-index: 20;
}

js

Page({
data: {
    openPicker: false,
    needAnimation : false,
    contentHeight: 0
},

onLoad: function () {

},

onReady: function () {
    var that = this;
    wx.getSystemInfo({
        success: function (res) {
            that.setData({
                //动态根据手机分辨率来计算内容的高度（屏幕总高度-顶部筛选栏的高度）
                contentHeight: (res.windowHeight - 72 * res.screenWidth / 750)
            });
        }
    })
},

onPickHeaderClick: function () {
    this.setData({
        openPicker: !this.data.openPicker,
        needAnimation : true
    })
  },
})

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