Get iteration index from List.map()

I wrote an iteration on list of letters and put inside cards on screen using "map" class.

In the code you can see that I made a row, and using "map" printed all the userBoard on cards to the screen. I want to add some logic inside so I need to get the id of the element (for taping event). Is there a way that I can do that?

Actually, I want to get a specific index of element over userBoard.

Code:

Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[
            Row(
              children: userBoard
                  .map((element) => Stack(children: <Widget>[
                        Align(
                          alignment: Alignment(0, -0.6),
                          child: GestureDetector(
                            onTap: (() {
                              setState(() {
                                // print("element=${element.toString()}");
                                // print("element=${userBoard[element]}");
                              });
                            }),
                            child: SizedBox(
                              width: 40,
                              height: 60,
                              child: Card(
                                  shape: RoundedRectangleBorder(
                                    borderRadius: BorderRadius.circular(5.0),
                                  ),
                                  child: Center(
                                    child: Text(element,
                                        style: TextStyle(fontSize: 30)),
                                  )),
                            ),
                          ),
                        )
                      ]))
                  .toList(),
            )
          ],
        ),
}

Picture - each card is "element" of the map. I want to get the indexes for the function onTap.

To get access to index, you need to convert your list to a map using the asMap operator.

Example

final fruitList = ['apple', 'orange', 'mango'];
final fruitMap = fruitList.asMap(); // {0: 'apple', 1: 'orange', 2: 'mango'}

// To access 'orange' use the index 1.
final myFruit = fruitMap[1] // 'orange'

// To convert back to list
final fruitListAgain = fruitMap.values.toList();

Your Code

userBoard.asMap().map((i, element) => MapEntry(i, Stack(
  GestureDetector(onTap: () {
    setState(() {
      // print("element=${element.toString()}");
      // print("element=${userBoard[i].toString()}");
    });
  }),
))).values.toList();

You can get index use list.indexOf when the list has no duplicate elements。

Example

userBoard.map((element) {
  // get index
  var index = userBoard.indexOf(element);
  return Container(
    
  );
}).toList()

The easiest approach if you want to iterate

We can extend Iterable with a new function:

import 'dart:core';

extension IndexedIterable<E> on Iterable<E> {
  Iterable<T> mapIndexed<T>(T Function(E e, int i) f) {
    var i = 0;
    return map((e) => f(e, i++));
  }
}

Usage:

myList.mapIndexed((element, index) {});

Taken from here.

Dart has released the collection package that comes with a mapIndexed extension to all Iterables.

import 'package:collection/collection.dart';

void main() {
  final fruitList = ['apple', 'orange', 'mango'];
  final withIndices = fruitList.mapIndexed((index, fruit) => "$index - $fruit");
  print(withIndices);
}

(DartPad)

The package comes with all sorts of handy extensions and useful tools to work with collections.

Another approach using List.generate:

var list = ['y', 'e', 's'];
var widgets = List.generate(list.length, (i) => Text(list[i]));

You can simply use the mapIndexed method:

userBoard.mapIndexed(
  (int index, element) => Container( ... ))
     .toList();

This is one of the many extensions from the FIC package: https://pub.dev/packages/fast_immutable_collections

---

If you don't want to add a package to your project you can just copy the extension itself:

extension FicListExtension<T> on List<T> {

  /// Maps each element of the list.
  /// The [map] function gets both the original [item] and its [index].
  Iterable<E> mapIndexed<E>(E Function(int index, T item) map) sync* {
    for (var index = 0; index < length; index++) {
      yield map(index, this[index]);
    }
  }
}

Note: I'm one of the authors of that package.

---

Update: I have now removed a few methods, like Iterable.mapIndexed() from the FIC package, because Google added a similar method to their collection package, and I want both packages to be compatible.

You can try this

children: [
          for(int index = 0; index < list.length; index++)
            Text(list[index])
        ]

You can use asMap() and entries.map() to get the index.

list.asMap().entries.map((e) {
      var index = e.key;
      var value = e.value;
      // ...
    }

You can use list.asMap()

var result = list.asMap().map((e) => '${e[0]} - ${e[1]});
print(result);

https://api.dartlang.org/stable/2.2.0/dart-core/List/asMap.html

There is no build-in function to get the iteration index.

What you probably want is a map which gives you the index:

children: enumerate(
  list,
  (index, item) => Text("event_$index")
).toList();

The implementation of enumerate is simple:

Iterable<E> enumerate<E, T>(
    Iterable<T> items, E Function(int index, T item) f) {
  var index = 0;
  return items.map((item) {
    final result = f(index, item);
    index = index + 1;
    return result;
  });
}

Another Solution is get hascode of your object is a unique as int example:

yourClass.hasCode()

this will return a id like 123456789 for each iteration

you when use in another widgets when you need

onSelectChanged: (d) {
    setState(() {
       selectedRow = d == true ? object.hascode : null;
    });
 },
 selected: object.hascode == selectedRow,

Can also try this:

list.asMap().keys.toList().map((index) {
  // var item = list[index];
  // index is the index of each element.
  return youFunction(index);
});

I also write other approaches as well in my blog here. https://medium.com/@channaly/map-with-index-in-dart-flutter-6e6665850ea8

You can use package:quiver's enumerate function first:

enumerate(userBoard).map((indexedValue) {
  final index = indexedValue.index;
  final element = indexedValue.value;
  // ...
})

Transform your list to another using map.

var yourList = ['A', 'B', 'C'];
var textList = yourList.map((e) => Text(e)).toList();

Usage:

Column(
  children: textList,
)

its pretty simple and straight forward in dart.

myList.map((item) =>
print(myList.indexOf(item));//here I printing index             
).toList()

The current version of built-in collection package now contains the method mapIndexed and comprehensive set of other List/Iterable extension methods.

import 'package:collection/collection.dart';

Map map = {
'1st':'first',
'2nd':'second'}; //any data

List mapAsList = map.keys.toList(); //convert map to list to get iteration index

print( map[mapAsList[0]] ); //first 
print( map[mapAsList[1]] ); //second

Try this: source

(Key in map) same (index in list)

myList.asMap().entries.map((entry) {
    int idx = entry.key;
    String val = entry.value;

    return something;
}