cancel method
Implementation
Future<void> cancel() async {
if (_downloadingStream != null) {
await _downloadingStream!.cancel();
if (_finalTask != null) {
_finalTask!.state = TaskState.canceled;
_streamController.add(_finalTask!);
} else {
_streamController.add(
ProcessTask(processed: 0, total: 0, state: TaskState.canceled));
}
}
}