Dartlang wait more than one future

Question

I want to do something after a lot of future function done,bu I do not know how to write the code in dart? the code like this:

for (var d in data) {   d.loadData().then() } // when all loaded // do something here 

but I don't want to wait them one by one:

for (var d in data) {   await d.loadData(); // NOT NEED THIS } 

how to write those code in dart?

Answer 1

You can use Future.wait to wait for a list of futures:

import 'dart:async';  Future main() async {   var data = [];   var futures = <Future>[];   for (var d in data) {     futures.add(d.loadData());   }   await Future.wait(futures); } 

DartPad example

Answer 2

Existing answer gives enough information, but I want to add a note/warning. As stated in the docs:

The value of the returned future will be a list of all the values that were produced in the order that the futures are provided by iterating futures.

So, that means that the example below will return 4 as the first element (index 0), and 2 as the second element (index 1).

import 'dart:async';  Future main() async {   print('start');    List<int> li = await Future.wait<int>([     fetchLong(),  // longer (which gives 4) is first     fetchShort(), // shorter (which gives 2) is second   ]);    print('results: ${li[0]} ${li[1]}'); // results: 4 2 }  Future<int> fetchShort() {   return Future.delayed(Duration(seconds: 3), () {     print('Short!');     return 2;   }); }  Future<int> fetchLong() {   return Future.delayed(Duration(seconds: 5), () {     print('Long!');     return 4;   }); }