registerCallback static method

Future<void> registerCallback(DownloadCallback callback, { int step = 10, })

Registers a callback to track the status and progress of a download task.

callback must be a top-level or static function of DownloadCallback type which is called whenever the status or progress value of a download task has been changed.

Your UI is rendered on the main isolate, while download events come from a background isolate (in other words, code in callback is run in the background isolate), so you have to handle the communication between two isolates.

Example:

ReceivePort _port = ReceivePort();

@override
void initState() {
 super.initState();

 IsolateNameServer.registerPortWithName(_port.sendPort, 'downloader_send_port');
 _port.listen((dynamic data) {
    String id = data[0];
    DownloadTaskStatus status = DownloadTaskStatus(data[1]);
    int progress = data[2];
    setState((){ });
 });

 FlutterDownloader.registerCallback(downloadCallback);
}

static void downloadCallback(
 String id,
 int status,
 int progress,
 ) {
   final SendPort send = IsolateNameServer.lookupPortByName(
   'downloader_send_port',
 );
 send.send([id, status, progress]);
}

Implementation

static Future<void> registerCallback(
  DownloadCallback callback, {
  int step = 10,
}) async {
  assert(_initialized, 'plugin flutter_downloader is not initialized');

  final callbackHandle = PluginUtilities.getCallbackHandle(callback);
  assert(
    callbackHandle != null,
    'callback must be a top-level or static function',
  );

  assert(
    0 <= step && step <= 100,
    'step size is not in the inclusive <0;100> range',
  );

  await _channel.invokeMethod<void>(
    'registerCallback',
    <dynamic>[callbackHandle!.toRawHandle(), step],
  );
}