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Using the ideas outlined in ding the article Using Dart with JSON Web Services at https://www.dartlang.org/articles/json-web-service/, I have been trying to implement the section on using JsonObject and interfaces to produce a strong typing of JSON data.

The article indicates that one should write something like. 

abstract class Language {
  String language;
  List targets;
  Map website;
}

class LanguageImpl extends JsonObject implements Language {
  LanguageImpl(); 

  factory LanguageImpl.fromJsonString(string) {
    return new JsonObject.fromJsonString(string, new LanguageImpl());
  }
}

However the compiler 'fail' at the definition of the class LanguageImpl with the message

Missing inherited members: 'Language.website', 'Language.targets' and 'Language.language'

Even more confusing the code will run without a problem....

Günter Zöchbauer
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richard
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  • You need to add the @proxy annotation to the LanguageImpl class, it's not inherited from JsonObject unfortunately. Gory details [here](https://code.google.com/p/dart/issues/detail?id=6111). – Greg Lowe Dec 12 '13 at 19:58

1 Answers1

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In Darteditor you get Quick fix support for this. Set the caret at LanguageImpl and press ctrl+1 or use the context menu > Quick fix. You get the missing concrete implementations you inherit from the abstract base class generated automatically.

Dart is a dynamic language and therefor very flexible. The tools support you and try to give meaningful warnings and hints about what could go wrong but don't prevent you running a program even when it is not yet finished.

You can use the @proxy annotation on the class to silent the warnings. This also needs the class to have a noSuchMethod() implementation.

Günter Zöchbauer
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  • thanks, but the concrete class should not implement the properties defined in the interface class as they will be 'implemented' by the JsonObject at run time via the method 'noSuchMethod'. I guess there should be an annotation to inhibit the compiler error message at that line.... – richard Dec 12 '13 at 09:21
  • I extended my answer. – Günter Zöchbauer Dec 12 '13 at 09:31