解决A generic error occurred in GDI+的问题

DNN Fck editor中的上传图片没有改变size的功能感觉很不方便，所以准备加一个改变图像size的功能。

因为不想改变UploadFile()这个DNN core method所以准备只是改动了fck editor 上传的页面
改动后的工作流程是：
1. 选择图片上传，调用DNN UploadFile()上传图片
2. 读取上传到server的file 另存为一个临时的Image
3. 调用GDI+ GetThumbnailImage改变Image尺寸覆盖原来的文件

问题随之而来，出现在第三步上运行到存储的时候总是出现A generic error occurred in GDI+

最后发现原因是:
To retain access to the source bits, GDI+ locks any source file, and forces the application to maintain the life of any source stream, for the life of the Bitmap or the Image object.

解决的方法是创建Index or Non-Indexed Image , 用Graphics.DrawImage() 来copy Image到一个新建立的Bitmap 对象然后多这个新的Image 执行Resize

Sample Code:

Bitmap bm1=(Bitmap)Image.FromFile("doodaa.gif");
2 解决A generic error occurred in GDI+的问题

Bitmap bm2=new Bitmap(bm1.Width,bm1.Height);
3 解决A generic error occurred in GDI+的问题

Graphics g=Graphics.FromImage(bm2);
4 解决A generic error occurred in GDI+的问题

g.DrawImageUnscaled(bm1,0,0);
5 解决A generic error occurred in GDI+的问题

//bm2 now contains a non-indexed version of the image.
6 解决A generic error occurred in GDI+的问题

//Now draw the X..
7 解决A generic error occurred in GDI+的问题

g.DrawLine(blah-blah 解决A generic error occurred in GDI+的问题

.);
8

g.DrawLine(blah-blah 解决A generic error occurred in GDI+的问题

.);
9

//get rid of the graphics
10 解决A generic error occurred in GDI+的问题

g.Dispose();
11 解决A generic error occurred in GDI+的问题

//and save a new gif
12 解决A generic error occurred in GDI+的问题

bm2.Save("foobar.gif",ImageFormat.Gif);
13 解决A generic error occurred in GDI+的问题

这里是微软的KB对这个问题的叙述:
http://support.microsoft.com/?id=814675