ASP.NET中通过对话框方式下载文件

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();

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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);