有时在Silverlight项目里我们需要让用户在Silverlight程序中点击截图按钮并将用户截取到的图片上传到服务器端进行处理,比如发送到FTP或者存储到数据库中. 但是由于WebService不能传递Image类型的参数,所以我们就需要先将用户截取到的图片编码成一个String传递到WebService端,然后再在WebService端解码成Image并进行处理.

参考示意代码如下:

public static string SaveScreenToString()
        {
            var bitmap = new WriteableBitmap(Application.Current.RootVisual, null);

            //Convert the Image to pass into FJCore
            int width = bitmap.PixelWidth;
            int height = bitmap.PixelHeight;
            int bands = 3;

            var raster = new byte[bands][,];

            for (int i = 0; i < bands; i++)
            {
                raster[i] = new byte[width, height];
            }

            for (int row = 0; row < height; row++)
            {
                for (int column = 0; column < width; column++)
                {
                    int pixel = bitmap.Pixels[width * row + column];
                    raster[0][column, row] = (byte)(pixel >> 16);
                    raster[1][column, row] = (byte)(pixel >> 8);
                    raster[2][column, row] = (byte)pixel;
                }
            }

            var model = new ColorModel { colorspace = ColorSpace.RGB };

            var img = new Image(model, raster);

            //Encode the Image as a JPEG
            var stream = new MemoryStream();
            var encoder = new JpegEncoder(img, 100, stream);

            encoder.Encode();

            //Move back to the start of the stream
            stream.Seek(0, SeekOrigin.Begin);

            //Get the Bytes and write them to the stream
            var binaryData = new Byte[stream.Length];
            long bytesRead = stream.Read(binaryData, 0, (int)stream.Length);

            return Convert.ToBase64String(binaryData);

        }

Web Service端代码

var binaryData = Convert.FromBase64String(imageStreamString);
var imageFilePath = Server.MapPath(System.Web.HttpContext.Current.Request.ApplicationPath) + "/Temp/snap.jpg";
if(File.Exists(imageFilePath))
{
     File.Delete(imageFilePath);
}             
var stream = new System.IO.FileStream(imageFilePath, FileMode.OpenOrCreate, FileAccess.ReadWrite);
stream.Write(binaryData, 0, binaryData.Length);
stream.Close();
PS: 代码中用到了FJ.Core.Dll,你可以从Google上下载这个文件,也可以从我的Dropbox里下载(由于GFW的原因Dropbox下载有可能不能访问).