问微信小程序picker日期选择器无效？

<view class="weui-cells weui-cells_after-title">

        <view class="weui-cell weui-cell_input">

          <view class="weui-cell__hd">

            <view class="weui-label">当前选择</view>

          </view>

          <view class="weui-cell__bd">

            <picker mode="date" value="{{date}}" start="2015-09-01" end="2017-09-01" bindchange="bindDateChange">

              <view class="weui-input">{{date}}</view>

            </picker>

          </view>

        </view>

      </view>