CODEWITHSUNDEEP
dart
Peter R
Peter R

Reputation: 3506

Dart - How to define a property that must be implemented in any classes inheriting?

If I do this:

abstract class Base {
  void doSomething();
}

class Sub extends Base {

}

I'll get a warning in my IDE that I haven't implemented doSomething in Sub. How do I do that same thing for properties. Let's say I have a class like this:

class BaseChannel {
  void connect() {
    Socket.connect(topic);
  }
}

class PostChannel extends BaseChannel {

}

PostChannel hasn't implemented a topic property here. Is there a way to do something in BaseChannel that signals that PostChannel needs to?

Upvotes: 1

Views: 1142

Answers (2)

lrn
lrn

Reputation: 71623

If you want all subclasses to implement a topic getter, you need to declare one as part of the interface of the superclass. Like you can declare an abstract method, you can also declare abstract fields and getters/setters.

Example:

abstract class BaseChannel {
  String get topic; // Abstract getter declaration.
  void connect() {
    Socket.connect(topic);
  }
}

class PostChannel extends BaseChannel {
  final String topic; // Implements the getter.
  PostChannel(this.topic);
}

With Dart 2.12 you will also be able able to declare "abstract fields":

  abstract final String topic;

or (if it needs a setter too)

  abstract String topic;

This will be equivalent with declaring an abstract getter, or an abstract getter/setter pair.

Upvotes: 4

mezoni
mezoni

Reputation: 11200

Two options. Separately for getters and setters. It depends on what you need.

abstract class BaseChannel {
  String get tipic;

  void set topic(String topic);
}

class PostChannel extends BaseChannel {
  //
}

Error:

Missing concrete implementations of 'getter BaseChannel.tipic' and 'setter BaseChannel.topic'.
Try implementing the missing methods, or make the class abstract.

You will need to implement some of this:

  • getter
  • setter
  • getter and setter
  • field

It all depends on what you declare abstract in the base class (getter, setter or both).

Upvotes: 0

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