asp.net中通過對(duì)話框方式下載文件

1 通過探出對(duì)話框提示文件下載或打開

2 通過自定義header讓特定的應(yīng)用程序打開文件 

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”) ); 

流傳送所使用的方法：

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);

關(guān)于content type(mime type)的參考url：

http://www.w3.org/tr/html4/types.html (概述) 

http://www.iana.org/assignments/media-types/ (詳細(xì)列表) 

常見問題解決方案：

1、當(dāng)從資源文件或者數(shù)據(jù)庫blob字段載入圖像出現(xiàn)錯(cuò)誤

錯(cuò)誤內(nèi)容：a generic error occurred in gdi+

代碼：

bitmap bmp = this.getglobalresourceobject(“resource”,”_bitmap”) as bitmap;
response.contenttype=”image/jpeg”;
bmp.save(response.outputstream, imageformat.jpeg); 
response.end();

解決方法，再創(chuàng)建一個(gè)實(shí)例接收從資源文件或者數(shù)據(jù)庫blob字段讀入的圖像內(nèi)容。

解決方案代碼： 

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、無法直接把png圖像存入到輸出流

原因：png是特殊的圖片格式

解決方案代碼：

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、解決緩存問題

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);