c# - UpoadOperationProgress 立即返回 bytessent = bytestosend

Question

在我成功完成上传操作后，我现在正在尝试获得一些进度 UI。现在这是我的代码，包括进度回调和该回调的处理程序。

public async Task<UploadOperation> BackgroundUploadVideoAsync(IStorageFile file, string gfyName)
{
    BackgroundUploader uploader = new BackgroundUploader();

    //… Create upload ...


    var partOperation = await uploader.CreateUploadAsync(new Uri("https://filedrop.gfycat.com/"), contentParts, "form-data", Guid.NewGuid().ToString() );
    var progress = new Progress<UploadOperation>(Shell.Current.HandleUpload);
    try
    {
        await partOperation.StartAsync().AsTask(progress);
        return partOperation;
        //var response = await operation.StartAsync().AsTask();
    }
    catch(Exception e)
    {

        var status = BackgroundTransferError.GetStatus(e.HResult);
        //await new MessageDialog($"An error occurred: {status}").ShowAsync();

    }
    return partOperation;
}

public async void HandleUpload(UploadOperation operation)
{
    await Dispatcher.RunAsync( Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
    {
        var percent = operation.Progress.BytesSent / operation.Progress.TotalBytesToSend;
        progressBar.Value = Math.Truncate((double)percent);
        });
    }
}

问题是当HandleUpload被调用时，'bytessent' 和 'bytestosend' 立即相等，我的进度条设置为 100% 并在那里等到任务完成。我以前从未处理过进度回调，所以我可能做错了。