小编Mm *_*ory的帖子

我正在尝试添加要调整的数量的选项，但是出现错误消息“必须向文本小部件提供非空字符串”如何在此代码中提供此信息？https://i.stack.imgur.com/Qp8pO.png

 trailing: Container(
        height: 60,
        width: 60,
        padding: EdgeInsets.only(left: 10),
        child: Column(
          children: <Widget>[
            new GestureDetector(child: Icon(Icons.arrow_drop_up), onTap: () {}),
            new Text(cart_prod_qty),
            new GestureDetector(child: Icon(Icons.arrow_drop_down), onTap: () {})
          ],
        ),

当我跑步时

brew tap heroku/brew && brew install heroku

我收到这个错误

The following formula cannot be installed from bottle and must be built from source.   
heroku