關閉的方法：向下滑動即可關閉。

onPressed: (){
           Scaffold.of(context).showBottomSheet((BuildContext context){
             return Row(
               mainAxisAlignment: MainAxisAlignment.spaceAround,
               children: <Widget>[
               IconButton(icon: Icon(Icons.shop_two), onPressed: (){

               }),
               IconButton(icon: Icon(Icons.shop_two), onPressed: (){

               })
             ],);
           });
       }),