UnauthorizedAccessException at storageFile.OpenReadAsync

Question

用户可以拍摄多张照片。这些图片存储在ApplicationData.Current.LocalFolder:

folderBatch = await ApplicationData.Current.LocalFolder.CreateFolderAsync("Batch", CreationCollisionOption.OpenIfExists);

当用户拍照时，这个方法被触发:

    public async void GetAndProcessImage()
    {
           IBuffer ImageBuffer = null;
            if (App.settings.ImageSource == MyImageSource.Camera)
                ImageBuffer = await Camera.TakePhotoAsync();
            // store in batch folder
            IReadOnlyList<StorageFile> listFiles = await folderBatch.GetFilesAsync();
            int iNumberOfFiles = listFiles.Count;
            StorageFile fileTarget = await folderBatch.CreateFileAsync(string.Format("batch{0}.jpg", iNumberOfFiles));
            IRandomAccessStream filestream = await fileTarget.OpenAsync(FileAccessMode.ReadWrite);
            await filestream.GetOutputStreamAt(0).WriteAsync(ImageBuffer);
            await filestream.FlushAsync();
} 

图片是用上面GetAndProcessImage调用的方法拍摄的:

    public async Task<IBuffer> TakePhotoAsync()
    {
        Debug.WriteLine("taking picture...");
        InMemoryRandomAccessStream stream = new InMemoryRandomAccessStream();
        if (mediaCapture.VideoDeviceController.FocusControl.Supported)
            await mediaCapture.VideoDeviceController.FocusControl.FocusAsync();
        try
        {
            await mediaCapture.CapturePhotoToStreamAsync(ImageEncodingProperties.CreateJpeg(), stream);
        }
        catch (Exception e)
        {
            ExceptionHandler.Instance.HandleException(e);
        }
        IBuffer ibuffer = await StreamHelpers.StreamToIBuffer(stream);
        return ibuffer;
    }

当用户完成后，他/她可以按下按钮开始读取批处理文件:

MyFile file = new KNFBFile(string.Format("{0}\{1}.knfb", ApplicationData.Current.LocalFolder.Path, string.Format("Batch-{0:yyyyMMdd-hh-mm-ss-tt}", DateTime.Now)));
uint iCount = 0;
foreach (StorageFile filebatch in listFiles)
{
     await App.converter.ConvertBatchJPG(filebatch);
     IRandomAccessStream imagestream = await StreamHelpers.IBufferToStream(App.ocr.LastImageBuffer);
     file.SavePage(iCount++, imagestream);
}

这个方法现在被称为:

 public async Task ConvertBatchJPG(StorageFile fileSource)
 {
      IRandomAccessStream JPGStream = await fileSource.OpenReadAsync();

——>上面的方法(OpenReadAsync)导致异常…}

Answer 1

您需要处理正在检索的outputstream的filestream 和:

StorageFile fileTarget = await folderBatch.CreateFileAsync(string.Format("batch{0}.jpg", iNumberOfFiles));
using(IRandomAccessStream filestream = await fileTarget.OpenAsync(FileAccessMode.ReadWrite))
{
    using(var outStream = filestream.GetOutputStreamAt(0))
    {
        await outStream.WriteAsync(ImageBuffer);
    }
    await filestream.FlushAsync();
 }

因为你没有改变OpenAsync()返回的流，你也可以避免创建一个中间输出流:

using(IRandomAccessStream filestream = await fileTarget.OpenAsync(FileAccessMode.ReadWrite))
{
    await filestream .WriteAsync(ImageBuffer);
    await filestream.FlushAsync();
 }