ASP编程：Using the Counters Object （1）

无法实现跨操作系统的应用。当然这也是微软的理由之一，只有这样才能发挥ASP最佳的能力。可是我却认为正是Windows限制了ASP，ASP的概念本就是为一个能让系统运行于一个大的多样化环境而设计的；objectIntroduction:
Inyesterdaysarticle,RecordingPageHitswithMicrosoftsPageCounterObjectweexaminedusingMicrosoftsPageCounterobjecttotrackthenumberofhitsforanyparticularWebpage.Unfortunatelythiscomponentisonlybuiltforcountingpageviewhits.Ifwewantedtocountsomethingelse,sayeachtimeauserenteredaparticularsearchqueryintooursitessearchpage,wedbehardpressedwithusingthePageCounterobject.FortunatelyMicrosoftalsoprovidesdeveloperswithamoregenericcountingobject,theCountersobject.Thisobjectcanbeusedtotrackanindeterminentnumberofdeveloper-definedcounters.

BoththePageCounterandCounterscomponentsaremadeavailablewithMicrosoftsIISResourceKit.UnfortunatelythereisshoddydocumentationfortheIISResourceKit-itseemstobeisntalledonIIS5(Windows2000)bydefault,butolderversionsofIISmaynothaveitproperlyinstalled.Refertothepreviousarticle,RecordingPageHitswithMicrosoftsPageCounterObject,formoreinformationontheIISResourceKitandhowtoobtainitifyoudonthaveitinstalled.

AssumingyouhavetheIISResourceKitcomponentsproperlyinstalledyoushouldbeabletocreateaninstanceoftheCountersobjectusingthefollowingcode:

<%Setobj=Server.CreateObject("MSWC.Counters")%>


IfyougetaServer.CreateObjectFailed,Invalidclassstringerrorthenthecomponentsarenotproperlyinstalled.(IfthisisthecaseyoushouldtrychangingMSWC.CounterstoIISSample.Countersandcrossyourfingers.)Ifyoureceivenosucherrormessagethenthecomponentisproperlyinstalled.

UsingtheCountersObject:
TheCountersobjectallowsyoutocreateanynumberofpersistentcounters.WhenusingtheCountersobjectitissmartesttocreateasinlgeapplication-wideinstanceofthisobject.WecanmosteasilydothisbyaddingthefollowinglinetothetopofourGlobal.asafile:

<OBJECTRUNAT=ServerSCOPE=ApplicationID=objCounterPROGID="MSWC.Counters"></OBJECT>


TolearnmoreaboutGlobal.asabesuretoread:EverythingyouWantedtoKnowaboutGlobal.asabutwereafraidtoAskandGlobal.asaEventsaswellastheCreatingaGlobal.asaFilesectionofthesamplechapterofSamsTeachYourselfASP3.0in21Days!

OncethislineisaddedtoGlobal.asayoucanaccesstheCountersobjectfromanyASPpageinyourWebsitebytheobjectsIDthatwespecifiedintheOBJECTtag:objCounter.LikethePageCounterobjectdiscussedinyesterdaysarticle,theCountersobjectisafairlysimpleobjectconsistingofonlyfourmethods:


Get(CounterName)-RetrievesthecurrentvalueofthecounterspecifiedbythenameCounterName

Increment(CounterName)-IncrementsthecurrentvalueofthecounterspecifiedbythenameCounterName

Remove(CounterName)-RemovesthecounterspecifiedbythenameCounterNamefromthetextfilecounters.txt.Thistextfileiswherethecounterinformationispersisted.

Set(CounterName,Value)-SetsthevalueofthecounterspecifiedbythenameCounterNametothevaluespecifiedbyValue
So,oncewehaveaddedtheOBJECTtagabovetoourGlobal.asafilewecanstartworkingwiththeCountersobjectfromanyASPpageonourWebsite.WecouldusetheCountersobjectmuchlikeweusedthePageCounterobject.Forexample,ifwewantedtocreateacountertoseehowmanyfolksvisitedourhomepagewecouldusethefollowingcodeonourhomepage:

<%
Incrementthehomepagecounter
objCounter.Increment("HomePage")

Displayhowmanyhitswevehad
Response.Write"Therehavebeen"&objCounter.Get("HomePage")&"hits."
%>




ThecounternameHomePagedoesntrepresentanyspecialsortofname.Youcansimplycreateacounterbyspecifyingauniquename.Oncethecounteriscreatedyoucanincrementit,changeit,getitscurrentvalue,orremoveitfromanypageonyourWebsite.So,ifonanotherpageyouhadthesamecodeasaboveandtenvisitorshityourhomepageandthenfivevisitorshitthissecondpage,thevaluefortheHomePagecounterwillbe15-10hitsfromthehomepageand5hitsfromthesecondarypage.

InPart2wellexaminetheCountersobjectinmoredetail,lookingathowandwhereitsvaluesarepersisted.Wellalsolookatsomecodetodisplayallofthevaluesofthevariouscounterswemayhavecreated!
</p>asp可以轻松地实现对页面内容的动态控制，根据不同的浏览者，显示不同的页面内容。而浏览者一点觉察不出来，就像为他专门制作的页面一样。使用各种各样的组件，asp可以完成无比强大的功能。