将 WriteableBitmap 保存到流

public static async Task<IRandomAccessStream> ConvertWriteableBitmapToRandomAccessStream(WriteableBitmap writeableBitmap)
{
    var stream = new InMemoryRandomAccessStream();

    BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream);
    Stream pixelStream = writeableBitmap.PixelBuffer.AsStream();
    byte[] pixels = new byte[pixelStream.Length];
    await pixelStream.ReadAsync(pixels, 0, pixels.Length);

    encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, (uint)writeableBitmap.PixelWidth, (uint)writeableBitmap.PixelHeight, 96.0, 96.0, pixels);
    await encoder.FlushAsync();

    return stream;
}

使用流将位图保存到文件。