// 弹出底部菜单列表模态对话框

Future<int> _showModalBottomSheet() {
  return showModalBottomSheet<int>(
    context: context,
    isScrollControlled: true,  //一：设为true，此时为全屏展示

    builder: (BuildContext context) {
      return SizedBox(         //二：返回一个有高度的SizedBox，对话框高度就是此高度
        height: 250,
        child: ListView.builder(
          itemExtent: 50,
          itemCount: _licenceItemList.length,
          itemBuilder: (BuildContext context, int index) {
            return ListTile(
              title: Text("$index"),
              onTap: (){
                // do something
                print("$index");
                Navigator.of(context).pop();
              },
            );
          },
        ),
      );
    },
  );
}