Delphi 包的应用英文.docx

Delphi 包的应用英文.docx

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Delphi包的应用英文

DynamicpackagesinDelphi -Morearticlesbythisauthor

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Abstract:

ApaperonhowtocreateandusedynamicpackagesinDelphi.ByVinoRodrigues.

AnydiscussionofadvancedpackageuseinDelphimustraisethequestion:

Whyusepackagesatall?

Design-timepackagessimplifythetasksofdistributingandinstallingcustomcomponents.Runtimepackages,whichareoptional,offerseveraladvantagesoverconventionalprogramming.Bycompilingreusedcodeintoaruntimelibrary,youcanshareitamongapplications.Forexample,allofyourapplications--includingDelphiitself--canaccessstandardcomponentsthroughpackages.Sincetheapplicationsdon'thaveseparatecopiesofthecomponentlibraryboundintotheirexecutables,theexecutablesaremuchsmaller-savingbothsystemresourcesandharddiskstorage.Moreover,packagesallowfastercompilationbecauseonlycodeuniquetotheapplicationiscompiledwitheachbuild.

Packagesareevenbetterwhentheyareuseddynamically.Packagesofferamodularlibraryapproachtodevelopingapplications.Attimethosemodulesmaybecomeanoptionalentityofyourapplication.TakeforexampleanaccountingsystemwithanoptionalHRmodule.Forsomeinstallationsyouwillneedtoinstalljustthebaseapplication--forothersyouwillinstallboththebaseapplicationandtheHRmodule.Thislevelofmodularizationcanbeeasilyachievedbyjustincludingtheoptionalpackagetotheinstallbase.InthepastthiswasusuallyachievedwithdynamicallyloadedDLLs,butwithDelphi'spackagetechnologyitiseasytomakeyourmodularclassespartandparcelofyourapplication.Classescreatedfrompackagesbecomeapplication-ownedandthuscaninteractwithyourapplicationclasses.

Runtimepackagesandyourapplication

ManydevelopersthinkthatDelphipackagesareaplacetoputcomponent--butapackagecan（andshould）alsobeusedtomodularizeanapplication.

Toshowhowtousepackagestomodularizeyourapplicationwewillcreateanexample:

1.CreateanewDelphiapplicationwith2forms:

Form1andForm2.

2.RemoveForm2fromtheauto-createdformlistintheProject|Options|Formsmenudialog.

3.DropabuttononForm1andaddthefollowingcodetotheOnClickeventhandler:

4.withTForm2.Create（Application）do

5.begin

6.ShowModal;

7.Free;

end;

8.RemembertoaddUnit2toUnit1'susesclause.

9.Saveandruntheproject.

Wehavecreatedasimpleapplicationthatshowsaformwithabuttonthatshowsanotherformwhenitisclicked.

ButwhatifwewantedtocreateForm2inareusablemodule?

Theansweris--PACKAGES!

TocreateapackageforForm2wewill:

1.Opentheprojectmanager（View|ProjectManager）

2.Right-clickontheProjectGroupandselect"AddNewProject..."

3.Select"Package"fromthe"New"itemslist.

4.YoushouldnowseethePackageeditor.

5.Selectthe"Contains"itemandpressthe"Add"button.

6.Nowusethe"Browse..."buttontoselect"Unit2.pas."

7.Thepackageshouldnowcontaintheunit"Unit2.pas."

8.Nowsaveandcompilethepackage.

Thepackageisnowcomplete.Youshouldhaveafilecalled"package1.bpl"inyourProjectsBPLdirectory.（TheBPListheBorlandPackageLibrary;theDCPistheDelphiCompiledPackage--sortofliketheDCUofaPASfile.）

That'sallthatneedtobedonetothepackage.Wenowneedtocompiletheoriginalapplicationwiththepackageoptionswitchedon.

1.Selecttheproject"Project1.exe"fromtheProjectManagerbydouble-clickingonit.

2.Right-clickandselect"Options..."（YoucanalsoselectProject|Options...fromthemenu.

3.Selectthe"Packages"tab.

4.Checkthe"Buildwithruntimepackages"checkbox.

5.Edittheedit-boxinthe"Runtimepackages"sectiontoread:

"Vcl50;Package1"andOKtheoptions. 

6.NOTE:

DonotremoveUnit2fromtheapplication.

7.Saveandruntheapplication.

Theapplicationwillrunandbehavejustlikebefore--thedifferencecanbeseeninthefilesize.Project1.exeisnowonly14Kasapposedtotheoriginal293K.IfyouusearesourceexplorertoviewthecontentsoftheEXEandtheBPLyouwillfindthatboththeDFMandthecodeforForm2nowresideinthepackage.

Delphiachievesthisbystaticallylinkinginthepackageatcompiletime.（That'swhyyoushouldn'tremovetheunitfromtheEXEproject.）

Justthinkofwhatcanbeachievedbydoingthis:

Onecouldcreatedatamodulesinpackagesandquicklymodifytheirsourceandonlydistributethenewpackagewhenourdata-accessruleshavechanged,likewhenwemovefromBDEbasedconnectivitytoADO.Or,wecouldcreateafromthatshow'sa"thisoptionisnotavailableinthisversion"messageinonepackage,andthenasimilarlynamedformthathasfunctionalityinasame-namedpackage.Wewillthenhavea"Pro"and"Enterprise"versionofourproductwithoutmucheffort.

Dynamicloadandunloadofpackages

StaticallylinkedDLLsandBPLsworkfineinmostcases,butwhatifwedecidenottodeploytheBPL?

Wewouldgeta"ThedynamiclinklibraryPackage1.bplcouldnotbefoundinthespecifiedpath..."errorandourapplicationwouldstopfunctioning.Orwhatif,inourmodularapplication,wewantedtohavenumerousplug-inlikemodules?

WeneedawaytodynamicallylinktotheBPLatruntime.

WithDLLsthisisasimpleprocessofusingtheLoadLibraryfunction.

functionLoadLibrary（

lpLibFileName:

PChar）:

HMODULE;stdcall;

OncetheDLLisloadedwecancallexportedfunctionsandprocedureswithintheDLLbyusingtheGetProcAddressfunction.

functionGetProcAddress（hModule:

HMODULE;

lpProcName:

LPCSTR）:

FARPROC;stdcall;

WefinallyunloadthedllbyusingtheFreeLibraryfunction.

functionFreeLibrary（hLibModule:

HMODULE）:

BOOL;

stdcall;

InthisexamplewewilldynamicallyloadMicrosoft'sHtmlHelplibrary:

functionTForm1.ApplicationEvents1Help（

Command:

Word;Data:

Integer;

varCallHelp:

Boolean）:

Boolean;

type

TFNHtmlHelpA=function（hwndCaller:

HWND;

pszFile:

PAnsiChar;uCommand:

UINT;

dwData:

DWORD）:

HWND;stdcall;

var

HelpModule:

HModule;

HtmlHelp:

TFNHtmlHelpA;

begin

Result:

=False;

HelpModule:

=LoadLibrary（'HHCTRL.OCX'）;

ifHelpModule<>0then

begin

@HtmlHelp:

=GetProcAddress（HelpModule,

'HtmlHelpA'）;

if@HtmlHelp<>nilthen

Result:

=HtmlHelp（Application.Handle,

PChar（Application.HelpFile）,

Command,

Data）<>0;

FreeLibrary（HelpModule）;

end;

CallHelp:

=False;

end;

DynamicallyloadedBPLs

BPLsarejustassimple.Wellalmost.

WedynamicallyloadthepackagebyusingtheLoadPackagefunction.

functionLoadPackage（constName:

string）:

HMODULE;

WecreateTPersistentClassoftheclasswewishtoinstantiatebyusingtheGetClassfunction.

functionGetClass（constAClassName:

string）:

TPersistentClass;

Instantiateanobjectoftheloadedclassanduseit.

Andwhenwearedone,unloadthepackageusingtheUnloadPackageprocedure.

procedureUnloadPackage（Module:

HMODULE）;

Letusgobacktoourexampleandmakeafewchanges:

1.Select"Project1.exe"fromtheprojectmanager.

2.Right-clickandselect"Options..."

3.Selectthe"Packages"tab.

4.Remove"Package1"fromthe"Runtimepackages"edit-boxsectionandOKtheoptions.

5.OnDelphi'stoolbar,clickonthe"Removefilefromproject"button.

6.Select"Unit2|Form2"fromthelistandthen"OK."

7.Nowgotothe"Unit1.pas"sourceandremoveUnit2fromitsusesclause.（ThesestepsarerequiredtoremoveanylinktoUnit2andthepackagewewishtoloaddynamically.）

8.GotothesourceofButton1'sOnClickevent.

9.AddtwovariablesoftypeHModuleandTPersistentClass.

10.var

11.PackageModule:

HModule;

AClass:

TPersistentClass;

12.LoadthepackagePackage1byusingtheLoadPackagefunction.

PackageModule:

=LoadPackage（'Package1.bpl'）;

13.CheckthatthePackageModuleisnot0（zero）.

14.CreateapersistentclassusingtheGetClassfunction,passingitthenameoftheformwithinthepackageasitsparameter:

AClass:

=GetClass（'TForm2'）;

15.Ifthepersistentclassisnotnil,createanduseaninstanceoftheclassjustabefore.

16.withTComponentClass（AClass）.Create（Application）

17.asTCustomFormdo

18.begin

19.ShowModal;

20.Free;

end;

21.Finally,unloadthepackageusingtheUnloadPackageprocedure:

UnloadPackage（PackageModule）;

22.Savetheproject.

HereisthecompletelistingoftheOnClickevent:

procedureTForm1.Button1Click（Sender:

TObject）;

var

PackageModule:

HModule;

AClass:

TPersistentClass;

begin

PackageModule:

=LoadPackage（'Package1.bpl'）;

ifPackageModule<>0then

begin

AClass:

=GetClass（'TForm2'）;

ifAClass<>nilthen

withTComponentClass（AClass）.Create（Application）

asTCustomFormdo

begin

ShowModal;

Free;

end;

UnloadPackage（PackageModule）;

end;

end;

Unfortunatelythat'snottheendofit.

TheproblemisthattheGetClassfunctionrequirestheclasstoberegisteredbeforethefunctioncanfindit.Usuallyformclassesandcomponentclassesthatarereferencedinaformdeclaration（instancevariables）areautomaticallyregisteredwhentheformisloaded.Buttheformisn'tloadedyet.Sowhereshouldweregistertheclass?

Theanswer:

inthepackage.Eachunitinthepackageisinitializedwhenthepackageisloadedandfinalizedwhenthepackageisunloaded.

Let'sreturntoourexampleandmakeafewchanges:

1.Double-clickon"Package1.bpl"intheprojectmanager;thiswillactivatethepackageeditor.

2.Clickonthe+symbolnextto"Unit2"inthe"Contains"section.Thiswillexpandtheunittree.

3.Double-clickon"Unit2.pas"toactivatetheunit'ssourcecode.

4.Scrolldowntotheendofthefileandaddaninitializationsection.