Flutter 如何从颤振响应阵列中提取变量？

我得到了数组的响应，我必须获取数组中存在的一些变量，并将其存储在手机的本地数据库中，当应用程序启动时，我必须检查数据库是否存在

Unitdata unitdata1 = new Unitdata(univ_year_semid:"18",semid: "2");
await _networkUtils.unitdata("http://hiddenmasterminds.com/web/index.php?r=jguest/allstudentsemdata",body: unitdata1.toMap());

这是我用来点击URL的代码片段

class Unitdata{
  final String univ_year_semid;
  final String semid;
  List subject, unit, topic;

  Unitdata({this.univ_year_semid,this.semid});

  factory Unitdata.fromJson(Map<List ,dynamic> json){
    return Unitdata(

      univ_year_semid: json['univ_year_sem_id'],
      semid: json['sem_id']
    );
  }
  Map toMap() {
    var map =  new Map<List,dynamic>();
    map[subject] = subject;
    map[unit]= unit;
    map[topic] = topic;
    return map;
  }
}

这是创建数据库的代码

 void _onCreate(Database db, int version) async {
    await db.execute("CREATE TABLE table_subject("
        "univ_spec_sub_id INTEGER PRIMARY KEY NOT NULL,"
        "univ_year_sem_id INTEGER,"
        "sem_id INTEGER,"
        "university_id INTEGER,"
        "master_course_id INTEGER"
        "subject_name TEXT"
        "subject_desc TEXT"
        "no_units INTEGER"
        "created_datetime TEXT"
        "updated_datetime TEXT"
        "created_by TEXT"
        "updated_by TEXT"
        "internship INTEGER"
        "info TEXT"
        ")");
    print("table_subject table created");
  }