Can not access this in a field initializer to read ...

原代码：

  Widget buttonSection = Container(
    child: Row(
      mainAxisAlignment: MainAxisAlignment.spaceAround,
      children: <Widget>[
        _buildButtonColumn(context, Icons.call, "Call"),
        _buildButtonColumn(context, Icons.near_me, "Route"),
        _buildButtonColumn(context, Icons.share, "Share"),
      ],
    ),
  );


Column _buildButtonColumn(BuildContext context, IconData icon, String label) {
    Color color = Theme.of(context).primaryColor;

    return Column(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      //列布局
      children: <Widget>[
        Icon(
          icon,
          color: color,
        ),
        Container(
          margin: EdgeInsets.only(top: 8.0),
          child: Text(
            label,
            style: TextStyle(
              fontSize: 12.0,
              fontWeight: FontWeight.w400,
              color: color,
            ),
          ),
        )
      ],
    );
  }

报异常:

Error: Can't access 'this' in a field initializer to read '_buildButtonColumn'.

更改后:

Widget getContainer() {
    return Container(
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          _buildButtonColumn(context, Icons.call, "Call"),
          _buildButtonColumn(context, Icons.near_me, "Route"),
          _buildButtonColumn(context, Icons.share, "Share"),
        ],
      ),
    );
  }