Dart (Flutter) map<String, String>.map has no toList() - dart

Question

I have a a map structure and I want to make a DropdownMenuItem<String> for each entry. What I try to do is to call .map().toList() like this
var _languages = {
'en': 'English 🇺🇸/🇬🇧',
'fr': 'French 🇫🇷',
'nl': 'Dutch',
'es': 'Spanish'
};
languages.map((key, value) => DropdownMenuItem(
value: key,
child: Text(v)
)).toList();
(if you are on a Windows, the US/GB is printed as text, if you are on any other platform, it will be flags). The problem now is twofold:
The return type 'DropdownMenuItem' isn't a 'MapEntry', as required by the closure's context.
The method 'toList' isn't defined for the type 'Map'.
How would I properly create a list out of a map? Is this not possible because a map is not an ordered collection?

Answer 1

Map<K, V>.map returns another Map, which isn't what you want.
You instead can create an Iterable from the Map first, and use Iterable.map, which returns another Iterable:
var menuItems = languages.entries
.map((mapEntry) =>
DropdownMenuItem(value: mapEntry.key, child: Text(mapEntry.value)))
.toList();
alternatively:
var menuItems = [
for (var mapEntry in languages.entries)
DropdownMenuItem(value: mapEntry.key, child: Text(mapEntry.value)),
];

Answer 2

The map method om Map is not the same as the map method on iterables (such as List). Instead of returning an Iterable, it returns a Map. As such, the inner method needs to return a MapEntry so the method can construct a new Map object to return. In order to convert this into a list, you need to convert the map itself into a list.
I'm assuming what you want to do is to take the entries in the map and map them to DropDownButton, where the language code is the button's value and the language text is the button's text. As such, you want to call map on _langages.entries, which gives you an Iterable of all the keys and values in the map. You can then call map on this iterable and it will do what you expect:
var _languages = {
'en': 'English 🇺🇸/🇬🇧',
'fr': 'French 🇫🇷',
'nl': 'Dutch',
'es': 'Spanish'
};
languages.entries.map((entry) => DropdownMenuItem(
value: entry.key,
child: Text(entry.value),
)).toList();

Answer 3

You cannot call a .map directly in a scenario like yours as returned type is a Map<K, V>, means is a reply of the original but transformed (if you need to transform it). In your scenario you need another kind of map that is an Iterable<dynamic>. To have that you have to pass by .entries which gives you a Iterable<MapEntry<K, V>> and then call on that .map which gives you a Iterable<T> where the returned T can be even pizza :).
here a small piece of code that helps you understand the concept:
final Map<String, String> _languages = {
'en': 'English 🇺🇸/🇬🇧',
'fr': 'French 🇫🇷',
'nl': 'Dutch',
'es': 'Spanish'
};
#override
Widget build(BuildContext context) {
return DropdownButton(
items: _languages.entries
.map((MapEntry element) => DropdownMenuItem(value: element.key, child: Text(element.value)))
.toList(),
onChanged: (value) {
/**/
},
);
}