问从服务器显示、下载和保存jpeg图像到Windows Phone 8相机胶卷

EN

private void downloadImg()
    {
        String uri = "http://timenewsfeed.files.wordpress.com/2013/12/doge.jpg";
        Uri imgUri = new Uri(uri, UriKind.Absolute);
        ImageSource imgSource = new BitmapImage(imgUri);

        Dispatcher.BeginInvoke(() =>
        {
            imageBox.Source = imgSource;
        }
        );
            using (var mediaLibrary = new MediaLibrary())
            {
                using (var stream = new MemoryStream())
                {
                    Debug.WriteLine("trying to save photo...");
                    var fileName = "HELLOWORLD.jpg";
                    BitmapImage img = new BitmapImage(imgUri);
                    img.CreateOptions = BitmapCreateOptions.None;
                    img.ImageOpened += (s, e) =>
                    {
                        WriteableBitmap bmp = new WriteableBitmap((BitmapImage)s);
                        bmp.SaveJpeg(stream, bmp.PixelWidth, bmp.PixelHeight, 0, 100);
                    };
                    stream.Seek(0, SeekOrigin.Begin);
                    Dispatcher.BeginInvoke(() =>
                    {
                        var picture = mediaLibrary.SavePicture(fileName, stream);
                    });
                    // or to cameraroll
                    Debug.WriteLine("photo saved");
                }
            }

    }