Dart: Using Async and Await in Loops

In Dart (and Flutter as well), you can perform synchronous operations sequentially in loops by using Future.forEach. The example program below will print the numbers from 1 to 10. Every time it finishes printing a number, it will wait for 3 seconds before printing the next number.

// kindacode.com
void main() async {
  final items = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  await Future.forEach(items, (item) async {
    print(item);
    await Future.delayed(const Duration(seconds: 3));
  });
}

If you want to get rid of the blue underline when calling the print() function, just add a kDebugMode check:

// kindacode.com
import 'package:flutter/foundation.dart';

void main() async {
  final items = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  await Future.forEach(items, (item) async {
    if (kDebugMode) {
      print(item);
    }
    await Future.delayed(const Duration(seconds: 3));
  });
}

Alternative

An alternative way is to use for … in syntax like this:

// kindacode.com
void main() async {
  final items = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  for (int item in items) {
    print(item);
    await Future.delayed(const Duration(seconds: 3));
  }
}

Further reading:

• 3 Ways to Cancel a Future in Flutter and Dart
• Dart: Converting a List to a Set and vice versa
• Sorting Lists in Dart and Flutter (5 Examples)
• Dart: Extract a substring from a given string (advanced)
• Working with MaterialBanner in Flutter
• Using Font Awesome Icons in Flutter

You can also check out our Flutter category page or Dart category page for the latest tutorials and examples.