如何在 Dartlang 中检索元数据？

Question

Dartlang 教程介绍 package:meta https://www.dartlang.org/docs/dart-up-and-running/contents/ch02.html#ch02-metadata

DartEditor 识别元数据，如上述教程所示。本教程还解释了如何创建自定义元数据并检索它。但是没有关于如何检索它的代码示例。

Answer 1

通过阅读 Polymer.dart 中的@published metadata 等一些实现，我找到了方法。 https://www.dartlang.org/articles/reflection-with-mirrors/ https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart-mirrors#id_reflect

这里是示例代码。

import 'dart:mirrors';

class todo {
  final String who;
  final String what;

  const todo(this.who, this.what);
}

@todo('akira', 'add something')
class Foo {
  @todo('naoto', 'do something')
  String fooVariable = 'a';

  @todo('kitano', 'change the name')
  void fooMethod() {

  }
}

void main() {
  InstanceMirror im = reflect(new Foo());
  ClassMirror classMirror = im.type;

  // ClassMirror
  classMirror.metadata.forEach((metadata) {
    print(metadata.reflectee.who); // -> akira
    print(metadata.reflectee.what); // -> add something
  });

  // VariableMirror   
  for (VariableMirror variable in classMirror.variables.values) {
    print(variable.metadata.first.reflectee.who); // -> naoto
    print(variable.metadata.first.reflectee.what); // -> do something
  }

  // MethodMirror
  classMirror.methods.values.forEach((MethodMirror method) {
    print(method.metadata.first.reflectee.who); // -> kitano
    print(method.metadata.first.reflectee.what); // -> change the name
  });
}