How to convert an Object type to a Map type (array) in Dart, so the variables become key/value pairs?
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2 Answers
/**
* Uses refection (mirrors) to produce a Map (array) from an object's
* variables. Making the variable name the key, and it's value the
* value.
*/
Map objectToMap(Object object)
{
// Mirror the particular instance (rather than the class itself)
InstanceMirror instanceMirror = reflect(object);
Map dataMapped = new Map();
// Mirror the instance's class (type) to get the declarations
for (var declaration in instanceMirror.type.declarations.values)
{
// If declaration is a type of variable, map variable name and value
if (declaration is VariableMirror)
{
String variableName = MirrorSystem.getName(declaration.simpleName);
String variableValue = instanceMirror.getField(declaration.simpleName).reflectee;
dataMapped[variableName] = variableValue;
}
}
return dataMapped;
}
Will convert recursively any JS object to a Dart map, list or scalar value:
/// js_interop.dart
import 'dart:js';
/// Converts the specified JavaScript [value] to a Dart instance.
dynamic convertToDart(value) {
// Value types.
if (value == null) return null;
if (value is bool || value is num || value is DateTime || value is String) return value;
// JsArray.
if (value is Iterable) return value.map(convertToDart).toList();
// JsObject.
return new Map.fromIterable(getKeysOfObject(value), value: (key) => convertToDart(value[key]));
}
/// Gets the enumerable properties of the specified JavaScript [object].
List<String> getKeysOfObject(JsObject object) => (context['Object'] as JsFunction).callMethod('keys', [object]);
Usage:
/// config.js
window.$environment = 'staging';
window.$config = {
name: 'FooBar',
params: {
assets: ['css', 'js'],
forceSsl: true
}
};
/// main.dart
import 'dart:js' as js;
import 'js_interop.dart';
void main() {
var environment = convertToDart(js.context[r'$environment']);
assert(environment is String);
assert(environment == 'staging');
var config = convertToDart(js.context[r'$config']);
assert(config is Map<String, dynamic>);
assert(config.length == 2);
assert(config['name'] is String);
assert(config['name'] == 'FooBar');
assert(config['params'] is Map<String, dynamic>);
assert(config['params'].length == 2);
assert(config['params']['forceSsl'] is bool);
assert(config['params']['forceSsl'] == true);
assert(config['params']['assets'] is List<String>);
assert(config['params']['assets'].length == 2);
assert(config['params']['assets'].first == 'css');
assert(config['params']['assets'].last == 'js');
}
Caveats: the created instance does not reflect the changes from the original JS object. If you need this feature, see: https://stackoverflow.com/a/20720378/1084485
