Flutter使用video_compress二次压缩报错：Bad state: Stream已被监听

我在Flutter应用里用video_compress包实现视频压缩功能，流程是用户选完视频后，跳转下一页前先执行压缩，压缩时显示带进度的对话框。第一次压缩正常，进度对话框也能正确显示，但第二次及之后压缩会抛出Bad state: Stream has already been listened to.错误，求问题原因及解决办法。

GalleryApi类代码 #

class GalleryApi {
  static Future<MediaInfo?> videoCompress(List<File?> file) async {
    try {
      await VideoCompress.setLogLevel(0);

      return VideoCompress.compressVideo(file.last!.path,
          quality: VideoQuality.LowQuality, includeAudio: true);
    } catch (e) {
      VideoCompress.cancelCompression();
    }
  }
}

首屏压缩方法代码 #

Future compressVideo() async {
    showDialog(
      context: context,
      barrierDismissible: false,
      builder: (context) => const Dialog(child: ProgressDialogWidget()),
    );

    final info = await GalleryApi.videoCompress(selectedAssets.value);

    Navigator.of(context).pop();

    final size = await selectedAssets.value.last!.lengthSync();
    final ogSize = (size / 1000000).round();

    selectedAssets.value.clear();
    selectedAssets.value.add(info!.file);

    Get.to(ImagePost(
      images: selectedAssets.value,
      isVideo: isVideo,
      ogSize: ogSize.toString(),
      blurHash: [],
    ));
  }

进度对话框代码 #

class _ProgressDialogWidgetState extends State<ProgressDialogWidget> {
  late Subscription subscription;
  double? progress;

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

    subscription = VideoCompress.compressProgress$
        .subscribe((progress) => setState(() => this.progress = progress));
  }

  @override
  void dispose() {
    VideoCompress.cancelCompression();
    subscription.unsubscribe;
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final value = progress == null ? progress : progress! / 100;
    final _height = MediaQuery.of(context).size.height;
    final _width = MediaQuery.of(context).size.width;
    return SizedBox(
      height: _height * 0.2,
      width: _width,
      child: Padding(
        padding: const EdgeInsets.all(20),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              "Please wait while it's compressing...",
              style: TextStyle(fontSize: _width * 0.03),
            ),
            SizedBox(
              height: _height * 0.02,
            ),
            Row(
              children: [
                Expanded(
                  child: LinearProgressIndicator(
                    value: value,
                    minHeight: _height * 0.015,
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

问题原因 #

• VideoCompress.compressProgress$是单订阅流（Single-Subscription Stream），这类流只能被监听一次，首次监听完成后流会自动关闭，二次监听时就会触发Bad state错误。
• 每次打开ProgressDialogWidget都会重新订阅该流，且dispose方法中存在语法错误：subscription.unsubscribe缺少括号，导致首次订阅未被正确取消，流资源未释放。

解决方案 #

1. 修复订阅取消的语法错误
   在ProgressDialogWidget的dispose方法中，将subscription.unsubscribe改为subscription.unsubscribe();，确保对话框销毁时正确取消订阅：

   @override
   void dispose() {
     VideoCompress.cancelCompression();
     subscription.unsubscribe(); // 补全括号
     super.dispose();
   }
   

2. 将单订阅流转为多订阅流
   使用asBroadcastStream()将compressProgress$转换为广播流，支持多次监听，修改initState中的订阅代码：

   @override
   void initState() {
     super.initState();
     subscription = VideoCompress.compressProgress$
         .asBroadcastStream() // 转为广播流
         .subscribe((progress) => setState(() => this.progress = progress));
   }
   

3. 额外优化建议

   • 每次压缩开始前，可主动取消之前可能存在的订阅，避免流资源占用；
   • 在GalleryApi.videoCompress方法中，压缩完成或异常时，可调用VideoCompress.cancelCompression()清理流状态，确保下次压缩时流处于可用状态。

内容的提问来源于stack exchange，提问作者Mohammed Bekele