Widget _buildBuyContent(BuyInfosEntity infos) {
  var content;
  if (infos != null && infos.isBuyGoods) {
    //如果数据不为空，则显示Text
    content = BuyButton(
      onPressed: () {},
    );
  } else {
    content = new Container(height: 0.0, width: 0.0);
  }
  return content;
}

根据返回的数据内容来确定此处要不要显示内容