flutter_downloader下载完成后获取下载任务失败问

flutter_downloader 我们用来下载照片,需求是下载后要保存到相册 在下载进度回调中需要获取相关的任务 拿到下载图片的路径,即可保存资源到相册
问题代码:

initDownLoad() async {
    if (!FlutterDownloader.initialized) {
      await FlutterDownloader.initialize(
          debug: BaseConfig.isDebug, ignoreSsl: true);
    }

    if (!_isInitialized) {
      await FlutterDownloader.registerCallback(downloadCallback);
    }
    _isInitialized = true;
  }
@pragma('vm:entry-point')
  static void downloadCallback(
      String id, DownloadTaskStatus status, int progress) async {
if (status.value == DownloadTaskStatus.complete.value &&
            progress == 100) {
    final list = await FlutterDownloader.loadTasksWithRawQuery(
          query: 'SELECT * FROM task WHERE task_id = \"$id\"');
      if (list != null && list.isNotEmpty) {
        return list.first.savedDir + '/' + (list.first.filename ?? '');
      }
}
  }

下载完成后 使用FlutterDownloader.loadTasksWithRawQuery获取相应的下载任务,来获取下载资源路径,但是明明已经初始化了下载器,但是调用该方法会触发assert(_initialized, 'plugin flutter_downloader is not initialized');
在该回调方法外部调用FlutterDownloader.loadTasksWithRawQuery就么有该问题,没找到具体的原因

解决:
看插件介绍是在回调方法中使用IsolateNameServer,同步下载进度,进行更改,代码为

@pragma('vm:entry-point')
  static void downloadCallback(
      String id, DownloadTaskStatus status, int progress) async {
    final SendPort? send =
        IsolateNameServer.lookupPortByName('downloader_send_port');
    send?.send([id, status.value, progress]);
  }

  initDownLoad() async {
    if (!FlutterDownloader.initialized) {
      await FlutterDownloader.initialize(
          debug: BaseConfig.isDebug, ignoreSsl: true);
    }

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

        sysDownloadProgress(id, progress, status.value);
        if (status.value == DownloadTaskStatus.complete.value &&
            progress == 100) {
          print('=========status: ${status.value}');

          String path = await AlbumDownloadManager().handleOriginPath(id);
          if (path.length > 0) {
            studySaveImage(bytesList: File(path).readAsBytesSync());
          }
        }
      });

      await FlutterDownloader.registerCallback(downloadCallback);
    }
    _isInitialized = true;
  }

更改后竟可以获取路径了,网上相关的资料比较少,在这里记录一下,有遇到相关问题的,同时找到原因的,希望不吝赐教

补充:

原因其实在callback方法的说明中已经给出
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.
意思是下载进度和UI刷新分属于两个不同的isolates,两个isolates的内存是不共享的,所以出现了开始的 在下载回调中获取任务提示下载器没有初始化,我们需要处理两个isolates的通信,所以修改后问题解决,具体的可参考这两篇文章
isolates
FlutterEngine
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