Windows Store C#: System.UnauthorizedAccessException writing image file

Question

I'm currently creating a Windows store app (C#) that pulls an image from a URL at a regular interval (every 3 seconds) and displays it on a page. The image is successfully downloaded to temporary app storage once, but I get an Access denied (UnauthorizedAccessException) the second time round.

This is most likely because my app is using the file as a source for a bitmap (so it's still open) when it tries to overwrite it with a new image.

Is there a workaround for this that avoids the concurrency problem?

public async void GetLocalImageAsync(string internetUri, string uniqueName)
   {
       //Set up the web request and pass credentials.
       HttpWebRequest request = (HttpWebRequest)WebRequest.Create(internetUri);
      request.Credentials = new NetworkCredential("james", "jam3s");
        //get response
          using (var response = await request.GetResponseAsync())
          {
              using (var stream = response.GetResponseStream())
              {
                  var desiredName = string.Format(uniqueName);
                  //create the file.
                  var file = await ApplicationData.Current.TemporaryFolder.CreateFileAsync(desiredName, CreationCollisionOption.ReplaceExisting);

                  using (var filestream = await file.OpenStreamForWriteAsync())
                  {
                      await stream.CopyToAsync(filestream);

                      //update the bitmap image with the file we just downloaded.
                      BitmapImage c1src = new BitmapImage(new Uri("ms-appdata:///temp/camera1imgsrc.png"));
                      camera1img.Source = c1src;

                  }
              }
          }


   }

Answer 1

Try to handle file with ReaderWriterLockSlim class. http://msdn.microsoft.com/en-us/library/system.threading.readerwriterlockslim.aspx

Answer 2

You could store each downloaded file with a different name (eg by adding a timestamp or sequential number to the root file name). After you download it, you can set the source to this new downloaded file and delete the previous one after that.