命名继承的构造函数，不在dart中接受参数

Question

I am trying to inherit a dart class with a named constructor and I want to pass data into the parent class using super and the named constructor through the child class.

I have tried many variations, but this should work according to the documentation. I am using Dart 2.0. Note: if I have one argument and not a named constructor it works.

class Person {

  String firstname;
  String lastname;
  String city;

//empty constructor
  Person();

//named constructors
  Person.setfirstlast(String firstname, String lastname);

//setters and getters ...
}

class Worker extends Person{

  String company;
  String title;
  double salary;
  String _memo;

  //empty constructor
  Worker(){
    _memo = "Great Worker";
  }

  //create named constructor  - WHY WILL SUPER.setfirstlast NOT WORK?

  Worker.setWorkerInfo( this.company, this.title, this.salary) :
     super.setfirstlast(firstname, lastname)
  {
      _memo = "Great Worker"; 
  } 
  //setters and getters ...
}

Here is the error message.

String firstname Only static members can be accessed in

initializers.dart(implicit_this_reference_in_initializer)

String lastname Only static members can be accessed in

initializers.dart(implicit_this_reference_in_initializer)

Thanks in advance!

---

** The Answer **

For those interested, I found the solution and this is how you code it. Dart has states that constructors and not inherited, but also includes super.

The 1 minute explanation is that you essentially create a new constructor in the child which includes the fields from the base class. Note, you use "this" for the child fields and you use the data type and placeholders for the inherited fields in the actual constructor. In this case, String fn and String ln. The place holders are then brought over via super.

  Worker.setWorkerInfo( this.company, this.title, this.salary, String fn, String ln) :
     super.setfirstlast(fn, ln)
  {
      _memo = "Great Worker"; 
  } 

Answer 1

The super.setfirstlast(firstname, lastname) references firstname and lastname . Those are not parameters to the Worker.setWorkerInfo constructor, and they are not declared in the surrounding lexical scope, so they instead implicitly refer to this.firstname and this.lastname .

You cannot refer to this in a constructor initializer list, which is what the error is trying to tell you ... just not very successfully, since it doesn't tell you what you are doing, only what you must do instead.

You likely want to add String firstname, String lastname as parameters to the Worker.setWorkerInfo constructor.

It has no bearing on the problem that the constructor happens to be named. The same problem would occur for an unnamed constructor.