Dart - Getting List of Fields and Methods in a Class

This tutorial shows you how to get all fields and methods in a class using Dart reflection library (mirrors).

In Object-Oriented Prorgramming where we can use and create classes, sometimes it's necessary to know what variables and methods does a class have. If you are using Dart and you need to get the list of fields (variables) and methods for a class, you can use Dart's reflection library by importing dart:mirrors.

For example, there are two classes: Product and Computer, the latter extends the former.

  class Product {
  
    final String name;
    final String description;
  
    const Product(this.name, this.description);
  }
  
  class Computer extends Product {
  
    final String processor;
    final String memory;
  
    Computer(name, description, this.processor, this.memory) : super(name, description);
  }

First, create an instance of the class - in this example, the Computer class. To use the reflection library, we need to get InstaneMirror by using reflect.

  InstanceMirror reflect(Object reflectee);

Then, get the ClassMirror by accessing type property of the InstanceMirror.

Example:

  Computer computer = new Computer(
    'Computer One',
    'No longer used',
    'Dual-core',
    '1GB'
  );
  InstanceMirror im = reflect(computer);
  ClassMirror classMirror = im.type;

After getting the ClassMirror instance, we can get the data member list using Mirror.declarations.values. Then, iterate through the list to get all fields (variables) and methods. The name for each data member can be obtained using MirrorSystem.getName as examplified below.

  for (var v in classMirror.declarations.values) {
      var name = MirrorSystem.getName(v.simpleName);

  }

To check the what kind of data member is being iterated, whether it's a variable or method, use v is VariableMirror and v is MethodMirror respectively. You may need to handle them differently as they have different properties. If you use if block like the below code, the runtimeType of v inside the if block will be the class used on the right hand side of is. Therefore, you can access the fields of the corresponding class.

Keep in mind that the mirror of a constructor is a MethodMirror. However, you can easily distinguish constructor using isConstructor field. The list of fields for VariableMirror and MethodMirror can be seen on the bottom of this tutorial.

  if (v is VariableMirror) {
    // Handle if data member is a variable
  } else if (v is MethodMirror) {
    // Handle if data member is a method
  }

With the code above, you'll only get the data members of the current class. To get the data members of the parent class, you need to get the ClassMirror of the parent class first.

  ClassMirror superClassMirror = classMirror.superclass;

Below is the full code. There is a function getDataMembers which is used for getting the data members of Computer class and its superclass (Product).

  import 'dart:mirrors';
  
  class Product {
  
    final String name;
    final String description;
  
    const Product(this.name, this.description);
  }
  
  class Computer extends Product {
  
    final String processor;
    final String memory;
  
    Computer(name, description, this.processor, this.memory) : super(name, description);
  }
  
  void getDataMembers(ClassMirror classMirror) {
    for (var v in classMirror.declarations.values) {
      var name = MirrorSystem.getName(v.simpleName);
  
      if (v is VariableMirror) {
        print('Variable: $name');
        print('const: ${v.isConst}');
        print('final: ${v.isFinal}');
        print('private: ${v.isPrivate}');
        print('static: ${v.isStatic}');
        print('extension: ${v.isExtensionMember}');
      } else if (v is MethodMirror) {
        print('Method: $name');
        print('abstract: ${v.isAbstract}');
        print('private: ${v.isPrivate}');
        print('static: ${v.isStatic}');
        print('extension: ${v.isExtensionMember}');
        print('constructor: ${v.isConstructor}');
        print('top level: ${v.isTopLevel}');
      }
  
      print('-----------------------------');
    }
  }
  
  void main() {
    Computer computer = new Computer(
      'Computer One',
      'No longer used',
      'Dual-core',
      '1GB'
    );
    InstanceMirror im = reflect(computer);
    ClassMirror classMirror = im.type;
    getDataMembers(classMirror);
  
    // Get data members of superclass
    ClassMirror superClassMirror = classMirror.superclass;
  
    if (superClass != null) {
      getDataMembers(superClassMirror);
    }
  }

That's how to get the data members of a class.

Getters of MethodMirror

Getters of VariableMirror