Promise (Future) in Dart

promise.dart

// example to convert base64 string to image

import 'dart:async'; // for Completer()
import 'dart:convert'; // for base64Decode()
import 'dart:ui' as ui; // for Image & decodeImageFromList()

Future<ui.Image> getImageFromString(String imageString) {
  var imageBytes = base64Decode(imageString);
  final Completer<ui.Image> completer = Completer();
  ui.decodeImageFromList(imageBytes, (image) => completer.complete(image));
  return completer.future;
}