ASP网页设计从Access数据库恢复BMP图象并显现在WEB...

缺乏可以共同遵循的行业标准，ASP还处在发展初期，大家对它的理解不同，如产品和服务标准，收费标准等，不利于行业的健康发展。HOWTO:RetrievingBitmapfromAccessandDisplayingInWebPage

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Theinformationinthisarticleappliesto:

ActiveServerPages
MicrosoftVisualBasicProfessionalandEnterpriseEditionsforWindows,versions5.0,6.0
ActiveXDataObjects(ADO),versions1.0,1.5,2.0,2.1SP2,2.5
MicrosoftInternetInformationServerversions4.0,5.0
MicrosoftDataAccessComponentsversion2.5

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SUMMARY
ThisarticleshowsbyexamplehowtoextractthebitmapphotosintheMicrosoftAccess97Northwind.mdb
database,andviewthemfromaWebbrowserusingActiveServerPages(ASP).Inordertoaccomplishthis
task,anActiveXDLLmustbecreatedthatstripstheAccessandOLEheadersfromthefield.Thisarticle
showshowtocreatethisActiveXDLL,andhowtoimplementit.



MOREINFORMATION
WARNING:ANYUSEBYYOUOFTHECODEPROVIDEDINTHISARTICLEISATYOUROWNRISK.Microsoftprovidesthis
code"asis"withoutwarrantyofanykind,eitherexpressorimplied,includingbutnotlimitedtothe
impliedwarrantiesofmerchantabilityand/orfitnessforaparticularpurpose.

ThisarticledemonstrateshowtouseVisualBasictoretrieveabitmapstoredinanOLEObjectfield.
BecausethedefinitionofOLEobjectstorageisnotdocumented,thefollowingcodesearchestheobjects
OLEheaderforcharactersconsistentwiththestartofthegraphic.Thismethodmaynotworkinall
circumstances.

BeawarethatInternetExplorer3.0isunabletodisplaytruecolorbitmaps.Forthisreason,thebitmaps
storedintheAccessdatabaseshouldbenohigherthan256colors.

Step-by-StepExampletoExtractthePhotos
CreateanewprojectinVisualBasicandmaketheprojectanActiveXDLL.


AddareferencetoActiveXDataObjects(ADO)byclickingtheProjectmenuandselectingReferences.
Select"MicrosoftOLEDBActiveXDataObjects1.0Library"andclickOK.


AddanewmoduletotheprojectbyselectingtheProjectmenuandclickingAddModule.SelectModuleand
clickOpen.


Placethefollowingcodeinthe(general)(declarations)sectionofMODULE1.BAS:

EnterthefollowingDeclarestatementasonesingleline:
PublicDeclareSubCopyMemoryLib"kernel32"Alias"RtlMoveMemory"
(lpvDestAsAny,lpvSourceAsAny,ByValcbCopyAsLong)

TypePT
WidthAsInteger
HeightAsInteger
EndType

TypeOBJECTHEADER
SignatureAsInteger
HeaderSizeAsInteger
ObjectTypeAsLong
NameLenAsInteger
ClassLenAsInteger
NameOffsetAsInteger
ClassOFfsetAsInteger
ObjectSizeAsPT
OleInfoAsString*256
EndType



Placethefollowingcodeinthe(general)(declarations)sectionofCLASS1.CLS:

FunctionDisplayBitmap(ByValOleFieldAsVariant)
DimArr()AsByte
DimObjHeaderAsOBJECTHEADER
DimBufferAsString
DimObjectOffsetAsLong
DimBitmapOffsetAsLong
DimBitmapHeaderOffsetAsInteger
DimArrBmp()AsByte
DimiAsLong

Resizethearray,thenfillitwith
theentirecontentsofthefield
ReDimArr(OleField.ActualSize)
Arr()=OleField.GetChunk(OleField.ActualSize)

Copythefirst19bytesintoavariable
oftheOBJECTHEADERuserdefinedtype.
CopyMemoryObjHeader,Arr(0),19

DeterminewheretheAccessHeaderends.
ObjectOffset=ObjHeader.HeaderSize+1

GrabenoughbytesaftertheOLEheadertogetthebitmapheader.
Buffer=""
Fori=ObjectOffsetToObjectOffset+512
Buffer=Buffer&Chr(Arr(i))
Nexti

MakesuretheclassoftheobjectisaPaintBrushobject
IfMid(Buffer,12,6)="PBrush"Then
BitmapHeaderOffset=InStr(Buffer,"BM")
IfBitmapHeaderOffset>0Then

Calculatethebeginningofthebitmap
BitmapOffset=ObjectOffset+BitmapHeaderOffset-1

Movethebitmapintoitsownarray
ReDimArrBmp(UBound(Arr)-BitmapOffset)
CopyMemoryArrBmp(0),Arr(BitmapOffset),UBound(Arr)-
BitmapOffset+1

Returnthebitmap
DisplayBitmap=ArrBmp
EndIf
EndIf
EndFunction



RenametheProjectbyselectingtheProjectmenu,andclickingon"Project1Properties"andtypeyournew
nameinthe"ProjectName"field.Thisexampleassumesthatyounamedtheproject"MyProject"andwill
refertothatnameinfuturesteps.


MaketheprojectApartmentModelThreadedbyselectingthe"UnattendedExecution"checkbox.ClickOK.


RenametheClassinthePropertyPane.Thisexampleassumesthatyounamedtheclass"MyClass"andrefers
tothatnameinfuturesteps.


CompiletheDLLbyclickingtheFilemenuandselecting"MakeMyProject.dll."


CreateanASPpagenamed"bitmap.asp"thatcontainsthefollowingcode:

<%@LANGUAGE="VBSCRIPT"%>
<%
YouneedtosetupaSystemDSNnamedNWindthatpointsto
theNorthwind.mdbdatabase
SetDataConn=Server.CreateObject("ADODB.Connection")
DataConn.Open"DSN=NWind","admin",""
SetcmdTemp=Server.CreateObject("ADODB.Command")
SetRS=Server.CreateObject("ADODB.Recordset")
cmdTemp.CommandText="SELECTPhotoFROMEmployees
WHEREEmployeeID=1"
cmdTemp.CommandType=1
SetcmdTemp.ActiveConnection=DataConn
RS.OpencmdTemp,,0,1
Response.ContentType="image/bmp"
SetBitmap=Server.CreateObject("MyProject.MyClass")
Response.BinaryWriteBitmap.DisplayBitmap(RS("Photo"))
RS.Close
%>



CreateanHTMLpagenamed"BitmapTest.htm"thatcontainsthefollowingcode:

<HTML>
<HEAD>
<TITLE>BitmapTest</TITLE>
</HEAD>
<BODY>
<HR>
<imgsrc="Bitmap.asp">
<HR>
</BODY>
</HTML>

对用户来说可预见费用、节约费用，可以做到花少钱办大事。由于省去了购买软件和硬件等的前期费用，用户可以租用较高级的应用软件。ASP的收费是根据软件的类型、客制化程度、用户数量、服务期限来定的，对客户来说这笔费用是可以预见的。方便于客户应用软件的升级。

不能只是将它停留在纸上谈兵的程度上。

ASP.Net和ASP的最大区别在于编程思维的转换，而不仅仅在于功能的增强。ASP使用VBS/JS这样的脚本语言混合html来编程，而那些脚本语言属于弱类型、面向结构的编程语言，而非面向对象，这就明显产生以下几个问题：

我想问如何掌握学习节奏(先学什么再学什么)最好详细点?

ASP.Net摆脱了以前ASP使用脚本语言来编程的缺点，理论上可以使用任何编程语言包括C++,VB,JS等等，当然，最合适的编程语言还是MS为.NetFrmaework专门推出的C(读csharp)，它可以看作是VC和Java的混合体吧。

我可以结合自己的经验大致给你说一说，希望对你有所帮助，少走些弯路。

以上是语言本身的弱点，在功能方面ASP同样存在问题，第一是功能太弱，一些底层操作只能通过组件来完成，在这点上是远远比不上PHP/JSP，其次就是缺乏完善的纠错/调试功能，这点上ASP/PHP/JSP差不多。

接下来就不能纸上谈兵了，最好的方法其实是实践。实践，只能算是让你掌握语言特性用的。而提倡做实际的Project也不是太好，因为你还没有熟练的能力去综合各种技术，这样只能使你自己越来越迷糊。

我想问如何掌握学习节奏(先学什么再学什么)最好详细点?