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中：

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

当用户拍照时，会触发此方法：

    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();
} 

这些图片是用此方法拍摄的，由上面的GetAndProcessImage调用：

    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;
    }

当用户完成时，他/她可以按一个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

您需要释放正在检索的filestream 和 outputstream：

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();
 }

由于您没有更改OpenAsync()返回的流，所以也可以避免创建中间输出流：

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