来自斯威夫特，这在斯威夫特很好用-

class Test {
    let userId: Int?
    let id: Int?
    let title: String?
    
    init(userId: Int, id: Int, title: String) {
        self.id = id
        self.title = title
        self.userId = userId
    }
    
}

现在，在尝试dart文档时，我尝试了这个方法，它工作正常

class Album {
   int? userId;
  int? id;
  String? title;

    Album({required int userId, required int id, required String title}) {
     this.userId = userId;
     this.id = id;
     this.title = title;
   }
  
}

但如果我要添加最终关键字，这是像让在swift它停止工作，我必须做一些事情，如下面-

class Album {
   final int? userId;
   final int? id;
    final String? title;

  
    const Album({required this.id, required this.userId, required this.title});
}

我不知道为什么这个工作，为什么下面的不-这只是我必须开始做的事情，或者背后有任何逻辑以及-

class Album {
   final int? userId;
   final int? id;
    final String? title;

    Album({required int userId, required int id, required String title}) {
     this.userId = userId;
     this.id = id;
     this.title = title;
   }
   
}