WeChatアプレットのドロップダウンメニュー実装方法の例（アニメーション付き）

<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>

/*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;
}

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
    })
  },
})