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Chapter 22.  Programming .NET and COM

Chapter 22.  Programming .NET and COM

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22.1.ImportingActiveXControls

ActiveXcontrolsareCOMcomponentstypicallydroppedintoa

form,whichmightormightnothaveauserinterface.When

MicrosoftdevelopedtheOCXstandard,whichallowed

developerstobuildActiveXcontrolsinVBandusethemwith

C++(andviceversa),theActiveXcontrolrevolutionbegan.

Overthepastfewyears,thousandsofsuchcontrolshavebeen

developed,sold,andused.Theyaresmall,easytoworkwith,

andaneffectiveexampleofbinaryreuse.

ImportingActiveXcontrolsinto.NETissurprisinglyeasy,

consideringhowdifferentCOMobjectsarefrom.NETobjects.

VisualStudio2005isabletoimportActiveXcontrols

automagically.AsanalternativetousingVisualStudio,

Microsofthasdevelopedacommand-lineutility,AxImp,thatwill

createtheassembliesnecessaryforthecontroltobeusedina

.NETapplication.



22.1.1.CreatinganActiveXControl

TodemonstratetheabilitytouseclassicActiveXcontrolsina

.NETapplication,firstdevelopasimplefour-functioncalculator

asanActiveXcontrolandtheninvokethatActiveXcontrolfrom

withinaC#application.BuildthecontrolinVB6,andtestitina

VB6application.Ifyoudon'thaveVB6ordon'twanttobother

creatingthecontrol,youcandownloadthecontrolfrommyweb

site(http://www.LibertyAssociates.com).

OncethecontrolisworkinginthestandardWindows

environment,you'llimportitintoyourWindowsForms

application.

Tocreatethecontrol,openVB6andchooseActiveXControlas



thenewprojecttype.Maketheprojectformassmallas

possiblebecausethiscontrolwillnothaveauserinterface.

Right-clickUserControl1andchooseProperties.Renameit

CalculatorinthePropertieswindow.ClicktheProjectinthe

ProjectExplorer,andinthePropertieswindow,renameit

CalcControl.Immediatelysavetheprojectandnameboththe

fileandtheprojectCalcControl,asshowninFigure22-1.



Figure22-1.CreatingaVBActiveXcontrol



Nowyoucanaddthefourcalculatorfunctionsbyright-clicking

theCalcControlform,selectingViewCodefromthepop-up

menu,andtypingintheVBcodeshowninExample22-1.



Example22-1.ImplementingtheCalcControl

ActiveXcontrol



PublicFunction_

Add(leftAsDouble,rightAsDouble)_

AsDouble

Add=left+right

EndFunction

PublicFunction_

Subtract(leftAsDouble,rightAsDouble)_

AsDouble

Subtract=left-right

EndFunction

PublicFunction_

Multiply(leftAsDouble,rightAsDouble)_

AsDouble

Multiply=left*right

EndFunction

PublicFunction_

Divide(leftAsDouble,rightAsDouble)_

AsDouble

Divide=left/right

EndFunction



Thisistheentirecodeforthecontrol.Compilethistothe

CalcControl.ocxfilebychoosingFile MakeCalcControl.ocxon

theVB6menubar.

Next,openasecondprojectinVBasastandardexecutable

(EXE).NametheformTestFormandnametheprojectCalcTest.

SavethefileandprojectasCalcTest.

AddtheActiveXcontrolasacomponentbypressingCtrl-Tand

choosingCalcControlfromtheControlstab,asshowninFigure

22-2.



Figure22-2.AddingtheCalcControltotheVB6

toolbox



Thisactionputsanewcontrolonthetoolbox,asshowncircled

inFigure22-3.



Figure22-3.LocatingCalcControlintheVB6

toolbox



DragthenewcontrolontotheformTestFormandnameit

CalcControl.Notethatthenewcontrolwillnotbevisible;this

controlhasnouserinterface.Addtwotextboxes,fourbuttons,

andonelabel,asshowninFigure22-4.



Figure22-4.BuildingtheTestFormuserinterface



NamethebuttonsbtnAdd,btnSubtract,btnMultiply,and

btnDivide.Allthatisleftisforyoutoimplementmethodsfor

handlingthebutton-clickeventsofthecalculatorbuttons.Each

timeabuttonisclicked,youwanttogetthevaluesinthetwo

textboxes,castthemtodouble(asrequiredbyCalcControl)

usingtheVB6CDblfunction,invokeaCalcControlfunction,

andprinttheresultinthelabelcontrol.Example22-2provides

thecompletesourcecode.



Example22-2.UsingtheCalcControlActiveX

controlinaVBprogram(TestForm)

PrivateSubbtnAdd_Click()

Label1.Caption=_

calcControl.Add(CDbl(Text1.Text),_

CDbl(Text2.Text))

EndSub

PrivateSubbtnDivide_Click()



Label1.Caption=_

calcControl.Divide(CDbl(Text1.Text),_

CDbl(Text2.Text))

EndSub

PrivateSubbtnMultiply_Click()

Label1.Caption=_

calcControl.Multiply(CDbl(Text1.Text),_

CDbl(Text2.Text))

EndSub

PrivateSubbtnSubtract_Click()

Label1.Caption=_

calcControl.Subtract(CDbl(Text1.Text),_

CDbl(Text2.Text))

EndSub



22.1.2.ImportingaControlin.NET

Nowthatyou'veshownthattheCalcControlActiveXcontrolis

working,youcancopytheCalcControl.ocxfiletoyour.NET

developmentenvironment.Onceyouhavecopiedit,remember

thattheCalcControl.ocxfilerequiresthatyouregisteritusing

Regsvr32.You'renowreadytobuildatestprogramin.NETto

usethecalculator:

Regsvr32CalcControl.ocx



Togetstarted,createaVisualC#WindowsapplicationinVisual

Studio2005(seeChapter13),nametheapplication

InteropTest,anddesignaform(suchastheTestFormform



youcreatedinVBintheprecedingsection)bydraggingand

droppingcontrolsontoit.NametheformTestForm.Acomplete

sampleformisshowninFigure22-5.



Figure22-5.BuildingaWindowsFormtotestthe

CalcControlActiveXcontrol



22.1.2.1Importingacontrol

TherearetwowaystoimportanActiveXcontrolintotheVisual

Studio2005developmentenvironment:youcanusetheVisual

Studio2005toolsthemselves,oryoucanimportthecontrol

manuallyusingtheaximputilitythatshipswiththe.NETSDK

Framework.TouseVisualStudio2005,chooseTools Choose

ToolboxItemsfromthemenu.Thisopensadialogbox.Onthe

COMComponentstab,findtheCalcControl.Calculatorobject

youjustregistered,asshowninFigure22-6.



Figure22-6.ImportingtheCalcControlActiveX

control



BecauseCalcControlisregisteredonyour.NETmachine,the

VisualStudio2005ChooseToolboxItemsdialog(ontheTools

menu)isabletofindit.Whenyouselectthecontrolfromthis

dialogbox,itisimportedintoyourapplication;VisualStudio

takescareofthedetails,includingaddingittoyourtoolbar.



22.1.2.2Manuallyimportingthecontrol

Alternatively,youcanopenacommandboxandimportthe

controlmanuallyusingtheaximp.exeutility,asshowninFigure

22-7.



Figure22-7.Runningaximp



aximp.exetakesoneargument,theActiveXcontrolyouwantto

import(CalcControl.ocx).Itproducesthreefiles:



AxCalcControl.dll

A.NETWindowscontrol



CalcControl.dll

Aproxy.NETclasslibrary



AxCalcControl.pdb

Adebugfile

Oncethisisdone,youcanreturntotheChooseToolboxItems

window,butthistimeselect.NETFrameworkComponents.You

cannowbrowsetothelocationatwhichthe.NETWindows

controlAxCalcControl.dllwasgeneratedandimportthatfileinto

thetoolbox,asshowninFigure22-8.



Figure22-8.Browsingfortheimportedcontrol



22.1.2.3Addingthecontroltotheform

Onceimported,thecontrolappearsonthetoolboxmenu,as

showninFigure22-9.Notethatthecontrolmayappearatthe

bottomofthetoolbox.



Figure22-9.ViewingtheAxCalcControlcalculator

afterimportingitintothetoolbox



NowyoucandragthiscontrolontoyourWindowsFormand

makeuseofitsfunctions,justasyoudidintheVB6example.



Addeventhandlersforeachofthefourbuttons.Theevent

handlerswilldelegatetheirworktotheActiveXcontrolyou

wroteinVB6andimportedinto.NET.

ThesourcecodefortheeventhandlersisshowninExample223.



Example22-3.Implementingeventhandlersfor

thetestWindowsForm



privatevoidbtnAdd_Click(objectsender,System.EventArgse)

{

doubleleft=double.Parse(textBox1.Text);

doubleright=double.Parse(textBox2.Text);

label1.Text=axCalculator1.Add(refleft,refright).ToStri

}



privatevoidbtnDivide_Click(objectsender,System.EventArgse)

{

doubleleft=double.Parse(textBox1.Text);

doubleright=double.Parse(textBox2.Text);

label1.Text=axCalculator1.Divide(refleft,refright).ToSt

}



privatevoidbtnMultiply_Click(objectsender,System.EventArgs

{

doubleleft=double.Parse(textBox1.Text);

doubleright=double.Parse(textBox2.Text);

label1.Text=axCalculator1.Multiply(refleft,refright).To

}



privatevoidbtnSubtract_Click(objectsender,System.EventArgs

{

doubleleft=double.Parse(textBox1.Text);

doubleright=double.Parse(textBox2.Text);

label1.Text=axCalculator1.Subtract(refleft,refright).To



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