多个picker 会出现页面联动 index错乱
解决方法1：
1、通过记录当前点击的对象在数组里的下标index
2、再赋值给当前下标为index的对象

<repeat for="{{selectedlist}}" key="templateList" index="index" item="template">
                  <view   wx:if="{{template.fieldname === '日期'}}">
                    <view class="user-name ub ub-ac item">
                      <view class="mark">
                        <text class="asterisk">*</text>日期
                      </view>
                      <view class="ub-f1 ub ub-ac"  @tap="recordIndex({{index}})">
                         <picker mode="date" name="birthday" value="{{template.value}}" bindchange="bindDateChange">
                          <view class="picker">
                            {{template.value}}
                          </view>
                         </picker>
                      </view>
                      <view class="icon iconfont icon-more select-item"></view>
                    </view>
                </view>
</repeat>


  data = {
    selectedlist:[], //
    operaIndex: 0  //记录所点击的index
  }

methods:{
    recordIndex(index){
      this.operaIndex = index;
      this.$apply()
    },
    bindDateChange: function(e) {
       console.log('picker发送选择改变，携带值为', e.detail.value)
       this.selectedlist[this.operaIndex].value = e.detail.value
       this.$apply()
    },

}