Flutter 解决 No Material widget found

Widget _buildPageContent(BuildContext context, Product product) {
    final double deviceWidth = MediaQuery.of(context).size.width;
    final double targetWidth = deviceWidth > 550.0 ? 500.0 : deviceWidth * 0.95;
    final double targetPadding = deviceWidth - targetWidth;
    return GestureDetector(
      onTap: () {
        FocusScope.of(context).requestFocus(FocusNode());
      },
      child: Material(
          child: Container(
        margin: EdgeInsets.all(10.0),
        child: Form(
          key: formkey,
          child: ListView(
            padding: EdgeInsets.symmetric(horizontal: targetPadding / 2),
            children: <Widget>[
              buildTitle(product),
              buildDesc(product),
              buildPrice(product),
              SizedBox(
                height: 10.0,
              ),
              buildSubmitButton()
            ],
          ),
        ),
      ),
    ));
  }