可以将方法放在initState中

class _MentionsState extends State<Mentions> {
  List<Map<String, dynamic>> data = [];
  void data1 (){
    for(int i = 0; i< widget.fullname.length; i++) {
      data.add({
         "Full Name": widget.fullname[i], 
         "username": widget.username[i], 
         "photourl" :widget.photourl[i] 
      });
    }
  )
}

 @override
 void initState() {
   super.initState();
    data1();
  }

 @override
 Widget build(BuildContext context) {
   return Container();
  }
}

试试这个：

class Mentions extends StatefulWidget {
  Mentions({
    required this.fullname,
    required this.username,
    required this.photourl,
    this.width,
    this.height,
    Key? key,
  }) : super(key: key) {
    for (var i = 0; i < fullname.length; i++) {
      users.add({
        'Full Name': fullname[i],
        'username': username[i],
        'photourl': photourl[i]
      });
    }
  }

  final double? width;
  final double? height;
  final List<String> fullname;
  final List<String> username;
  final List<String> photourl;
  late final List<Map<String, dynamic>> users;

  @override
  _MentionsState createState() => _MentionsState();
}

class _MentionsState extends State<Mentions> {...}

那么你可以只在_MentonsState中使用widget.users。但是你甚至可以不在小部件构造器中设置所有这些列表，在之前Map到用户，并且只为小部件构造器设置一个包含用户的列表。你真的需要有状态的小部件而不是无状态的吗？