从 List.map()获取迭代索引

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

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();

References to other answers

• I like this answer better. Please take a look.
• If you want in multiple places try extending like this.
• Alternatively, you could also try the dart collection approach.

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()

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,

Another approach using List.generate:

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

You can use ABC0's enumerate function first:

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

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.

You can try this

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

Transform your list to another using map.

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

Usage:

Column(
children: textList,
)

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

its pretty simple and straight forward in dart.

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

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

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

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.

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;
}

You can do it by defining a variable named index:

Widget listWidget() {


List < String > myList = ['A', 'B', 'C'];


int index = -1;


return Column(
children: myList.map < Widget > ((element) {
index++;
return Container(
Text("$index : $element")
);
}).toList()
);
}