ASP.NET中通过对话框方式下载文件
1 通过探出对话框提示文件下载或打开
2 通过自定义Header让特定的应用程序打开文件
使用的方法：Response.TransmitFile()
例程：
Response.ContentType = "image/jpeg";
Response.AppendHeader("Content-Disposition","attachment; filename=SailBig.jpg");
Response.TransmitFile( Server.MapPath("~/images/sailbig.jpg") );
流传送所使用的方法：Response.BinaryWrite()和Response.OutputStream()
例程：
Bitmap bmp = wwWebUtils.CornerImage(backcolor, color, c, Radius, Height, Width);
Response.ContentType = "image/jpeg";
Response.AppendHeader("Content-Disposition","attenment; filename=LeftCorner.jpg");
bmp.Save(Response.OutputStream, ImageFormat.Jpeg);
关于Content Type(MIME Type)的参考URL：
http://www.w3.org/TR/html4/types.html (概述)
http://www.iana.org/assignments/media-types/ (详细列表)
常见问题解决方案：
1、当从资源文件或者数据库BLOB字段载入图像出现错误
错误内容：A generic error occurred in GDI+
代码：
Bitmap bmp = this.GetGlobalResourceObject(“Resource”,”_BitMap”) as Bitmap;
Response.ContentType=”image/jpeg”;
bmp.Save(Response.OutputStream, ImageFormat.Jpeg);
Response.End();
解决方法，再创建一个实例接收从资源文件或者数据库BLOB字段读入的图像内容。
解决方案代码：
Bitmap bmp = this.GetGlobalResourceObject(“Resource”, ”_BitMap”) as Bitmap;
Bitmap temp = new Bitmap(bmp);
Response.ContentType = “image/jpeg”;
Temp.Save(Response.OutputStream, ImageFormat.Jpeg);
bmp.Dispose();
temp.Dispose();
Response.End();
2、无法直接把PNG图像存入到输出流
原因：PNG是特殊的图片格式
解决方案代码：
Bitmap bmp = this.GetGlobalResourceObject( “Resource”, “_BitMap”) as Bitmap;
Bitmap temp = new Bitmap(bmp);
MemoryStream ms = new MemoryStream();
Response.ContentType=”image/png”;
temp.Save(ms, System.Drawing.Imaging, ImageFormat.Png);
Ms.WriteTo(Response.OutputStream);
bmp.Dispose();
temp.Dispose();
Response.End();
3、解决缓存问题
Response.ContentType=”image/png”;
Response.Buffer = false;
Response.Clear();
MemoryStream stream1 = new MemoryStream();
// DrawPie method return an Image
This.DrawPie(table1).Save(stream1,ImageFormat.Png);
Response.BinaryWrite(stream1.ToArray());
Base.OnPreInit(e);