Closing a StreamController calls onCancel and emits done event

streamcontroller_close_fires_oncancel_and_ondone.dart

import 'dart:async';

void main() {
  var controller;
  controller = StreamController(onListen: () {
    for (final number in [1, 2]) {
          controller.add(number);
        }
        controller.close();
  },
  onCancel: () => print('onCancel'));
  controller.stream.listen(print, onDone: () => print('onDone'));
}