flutter-dart语言类型后加问号_SGdaodao的博客_dart 问号

flutter dart语言类型后加问号

class ListItemWidget extends StatefulWidget {
  const ListItemWidget({Key? key,
    this.icon,
    required this.title,
    this.content,
    this.OnTap,
  }) : super(key: key);

  final IconData? icon;
  final String title;
  final String? content;
  final VoidCallback? OnTap;


  @override
  _ListItemWidgetState createState() => _ListItemWidgetState();
}
class ListItemWid