CODEWITHSUNDEEP
flutterdartreflection
Jonathan Rhein
Jonathan Rhein

Reputation: 1723

Flutter: Convert String to class field name during runtime

Is it possible to "convert" a String which is dynamically generated in my code, into a class field/variable name?

The issue I am facing is that I have a database which returns a unique name (as String) for each of its rows. I want to use this name in order to find the corresponding field (with the same spelling as the database entry) of a generated class that holds all my translations within its various fields. As this class is generated and subject to constant change there is no way to convert into a Map and thereby access its fields as values as explained here.

My code:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  // Suppose this is a dynamic list returned from a database query
  final List<String> listFromDB = ['one', 'three', 'two'];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView.builder(
          itemCount: listFromDB.length,
          itemBuilder: (context, index) =>
              _listItemBuilder(context, index, listFromDB)),
    );
  }
}

Widget _listItemBuilder(BuildContext context, int index, List<String> listFromDB) {
  // suppose this is some map with translations of different languages. 
  final labels = Labels.translations['languageCode'];

  final String dbUniqueName = listFromDB[index];
  // QUESTION: How can I use the above String dbUniqueName to access a field of the
  // AnyClass class in order to return the corresponding value, e.g. "eins" for 
  // its name "one"?
  
  print(labels.dbUniqueName) // ERROR: Not compiling because dbUniqueName is a String


  return null;
}

// GENERATED: The below code can not be changed as it is generated

class Labels {
  static final Map<String, AnyClass> translations = {
    'languageCode' : AnyClass(one: 'eins', two: 'zwei', three: 'drei')
  };
}

class AnyClass {
  AnyClass({this.one, this.two, this.three});

  final String one;
  final String two;
  final String three;
}

I have read this old thread on GitHub on the same issue. But it seems there was no solution at that time. I also came across reflections in Dart but I am not sure whether they provide a solution in the above described case.

Thanks for any help and advice!

Upvotes: 2

Views: 3225

Answers (2)

Jonathan Rhein
Jonathan Rhein

Reputation: 1723

You usually use methods like the one below in Dart language to reference a class variable using a String.

Widget _listItemBuilder(
    BuildContext context, int index, List<String> listFromDB) {
  final labels = Labels.translations['languageCode'];

  final String dbUniqueName = listFromDB[index];

  print(getByFieldName(dbUniqueName, labels));

  return null;
}

String getByFieldName(String name, AnyClass anyClass) {
  switch (name) {
    case 'one':
      return anyClass.one;
    case 'one':
      return anyClass.one;
    case 'one':
      return anyClass.one;
    default:
      throw ('Unsupported');
  }
}

Upvotes: 2

Bram
Bram

Reputation: 680

Reflection is provided in the mirrors package, but that package requires the VM and is therefore not supported in Flutter. Have you looked at the reflectable package?

If that doesn't work, a simple Map could do the trick of translating a String in to an object's field, e.g.:

var object = AnyClass();
var field = {'one': object.one, 'two' object.two, 'three': object.three};
print(field['two']); // will print object.two;

Upvotes: 2

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