使用 StorageFile 在使用它读取图像之前获取位图尺寸？

Question

好的，我正在尝试分析 WPF 应用程序中图像的启发式方法。当用户选择图像文件位置时，我想在代码隐藏中打开图像，检查图像的颜色，并将它们输出到应用程序中。但是，要正确检查图像的像素，我需要获取尺寸以将其加载到可以获取像素颜色的WriteableBitmap。

当我第二次打开文件的流时，应用程序就会挂起。代码如下：

    private static async Task<Dictionary<Color, int>> GetColorCountsAsync(string path)
    {
        var colorCounts = new Dictionary<Color, int>();

        var absolutePath = string.Format(@"{0}\{1}",Directory.GetCurrentDirectory(),path);

        var dimension = await GetBitmapDimensions(absolutePath); //Method below - opens via StorageFile

        var file = await StorageFile.GetFileFromPathAsync(absolutePath); //Hangs forever
        using (var stream = await file.OpenStreamForReadAsync().ConfigureAwait(false))
        {
            var pixelWidth = dimension.Width;
            var pixelHeight = dimension.Height;
            var bitmap = new WriteableBitmap(pixelWidth, pixelHeight);

            bitmap.SetSource(stream.AsRandomAccessStream());

            using (var buffer = bitmap.PixelBuffer.AsStream())
            {
                var pixels = new byte[4 * pixelWidth * pixelHeight];
                buffer.Read(pixels, 0, pixels.Length);

                for (var y = 0; y < pixelHeight; y++)
                {
                    for (var x = 0; x < pixelWidth; x++)
                    {
                        var index = ((y * pixelWidth) + x) * 4;

                        var alpha = pixels[index + 4];
                        var red = pixels[index + 2];
                        var green = pixels[index + 1];
                        var blue = pixels[index + 0];
                        var color = Color.FromArgb(alpha, red, green, blue);

                        if (!colorCounts.ContainsKey(color))
                        {
                            colorCounts.Add(color, 0);
                        }
                        colorCounts[color] = colorCounts[color] + 1;
                    }
                }
            }
        }

        return colorCounts;
    }
    private static async Task<Dimension> GetBitmapDimensions(string absolutePath)
    {
        var file = await StorageFile.GetFileFromPathAsync(absolutePath);
        var bitmapImage = new BitmapImage();
        using (var fileStream = await file.OpenAsync(FileAccessMode.Read))
        {
            bitmapImage.SetSource(fileStream);
        }

        return new Dimension { Height = bitmapImage.PixelHeight, Width = bitmapImage.PixelWidth };
    }

我无法关闭位图图像也无法处理它 - 是什么导致应用程序冻结？

Answer 1

您不需要正确尺寸的位图，因为SetStream() 是一种扩展方法。它只需要一个对象，这样调用它：

  var bitmap = new WriteableBitmap(1,1).SetSource(stream.AsRandomAccessStream());