// 返回一个controller
  Future<int> _showBottomSheet(BuildContext context){
      return showModalBottomSheet<int>(
        // 1.设置圆角
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.only(topLeft: Radius.circular(ScreenUtil().setWidth(10)),
                                         topRight: Radius.circular(ScreenUtil().setWidth(10)))
        ),
        context: context,
            // 2.设置可以全屏
      //  isScrollControlled: true,
        builder: (BuildContext context){
            // 3.设置状态可以交互
            return StatefulBuilder(
                builder: (BuildContext context, StateSetter setState){
                  return Container(
                    child: Stack(
                      children: [
                        Column(
                          children: [
                            Container(
                              child: Text("购物篮"),
                            ),
                            Container(
                              child: Text("列表页面"),
                            )
                          ],
                        ),
                        Positioned(
                          left: 0,
                          bottom: 0,
                          right: 0,
                          child: Container(
                            child: Text("aaaaaaa"),
                          ))
                      ],
                    ),
                  );
                }
            );
        });
  }

关于showBottomSheet的用法

showBottomSheet(
                                  context: context,
                                  builder: (context) {
                                    return Container(
                                      decoration: BoxDecoration(
                                        color: Colors.lightBlue,
                                        borderRadius: BorderRadius.only(topLeft: Radius.circular(ScreenUtil().setWidth(10)),
                                                                        topRight: Radius.circular(ScreenUtil().setWidth(10)))
                                      ),
                                        height: ScreenUtil().setHeight(600),
                                    );
                                  });