Yakov Fain - Design Patterns a Deep Dive
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Design Pa*erns, a Deep Dive By Yakov Fain Farata Systems (c) Farata Systems
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Design patterns suggest approach to common problems that arise during software development regardless of what programming language. But implementation of these patterns is specific to the language. The main goal of this presentation is to highlight selected patterns as they may be implemented taking advantages of Flex framework.You'll see a not so obvious implementation of a Singleton, how a Proxy can dramatically change the behavior of an object, why a Mediator is a must-have in each Flex application. Do you know how to write Data Transfer Objects that are so important in Flex remoting? If time permits, we'll review the Class Factory pattern too.
Transcript of Yakov Fain - Design Patterns a Deep Dive
DesignPa*erns,aDeepDive
ByYakovFainFarataSystems
(c)FarataSystems
2
Farata Systems: What do we wo
Consulting and training
Software development (for free) (open source project Clear Toolkit on Sourceforge.net)
Writing tech. books and articles on Java and Adobe Flex (making from $0 to $1 per hour)
www.faratasystems.com
($$$$$$$$$$$$$$$$$$)
Whatisthisabout?
Designpa*ernssuggestanapproachtocommonproblemsthatariseduringsoCwaredevelopmentregardlessofwhatprogramminglanguageyouuse.
ButthegoalofthispresentaGonistohighlightselectedpa*ernsasyoumayimplementthemtakingadvantageoftheFlexframework.
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We’lltalkaboutthesepa*erns
• Singleton• Proxy• Mediator
• DataTransferObject• AsynchronousToken
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SingletonYoucancreateonlyoneinstanceofsuchaclassThere’snoprivateconstructorsinAcGonScript
ConsiderasamplefileMySingleton.as
packagesomePackage{publicclassMySingleton{
privatestaGcconst_instance:MySingleton=newMySingleton(Lock);publicstaGcfuncGongetinstance():MySingleton{return_instance;}publicfuncGonMySingleton(lock:Class){if(lock!=Lock){thrownewError("IllegalinstanGaGon.");}}}//EndofpackageclassLock{}
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Haveyoueverseenthis?
varmodel:AppModelLocator=AppModelLocator.getInstance();
andthis?service=ServiceLocator.getInstance().getHTTPService('loadEmployeesService');
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EnhancingtheApplicaGonobjectpublicdynamicclassDynamicApplica5onextendsApplica5onimplementsIApplicaGonFacade{publicfuncGonDynamicApplicaGon(){
super();}
publicstaGcvarservices:DicGonary=newDicGonary();
publicfuncGongetService(name:String):Object{ returnservices[name];}publicfuncGonaddService(name:String,value:Object):void{ services[name]=value;}publicfuncGonremoveService(name:String):void{ deleteservices[name];}publicfuncGongetServices():DicGonary{ returnservices;}
}
TheIApplicaGonFacadejustdeclaresthesefourmethodstoenableFlexBuilder’sintellisensehelpwhencasGng.var myApp:IApplicationFacade = …
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AddinganyproperGestomyModel
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SampledynamicapplicaGon(beginning)<?xmlversion="1.0"encoding="uc‐8"?><fx:DynamicApplicaGonxmlns:mx="h*p://www.adobe.com/2006/mxml"layout="absolute"xmlns:fx="h*p://www.faratasystems.com/2009/components"creaGonComplete="addAllServices();"><mx:Script>
<![CDATA[importcom.farata.core.DynamicApplicaGon;importmx.core.ApplicaGon;
//AddrequiredservicestotheApplica3onobject,i.e.myModelandmyServicesprivatefunc5onaddAllServices():void{
DynamicApplicaGon.services["myModel"]=newObject(); DynamicApplicaGon.services["myServices"]=newObject(); }
privatefunc5ongetData(serviceName:String,key:Object):Object{
returnDynamicApplicaGon.services[serviceName][key];}
privatefunc5onsetData(serviceName:String,key:Object,value:String):void{
DynamicApplicaGon.services[serviceName][key]=newString(value);}
]]></mx:Script> (c)FarataSystems
<!‐‐AddingvaluestomyModel‐‐><mx:Bu*onlabel="AddtomyModel"x="193"y="59”click="setData('myModel',key.text,value.text)"/>
<mx:Labelx="14"y="42"text="Key"fontWeight="bold"/><mx:Labelx="14"y="14"fontWeight="bold"fontSize="14"><mx:text>Addoneormorekey/valuepairstotheobjectMyModel</mx:text>
<mx:Labelx="91"y="42"text="Value"fontWeight="bold"/><mx:TextInputx="8"y="59"id="key"width="75"/><mx:TextInputx="89"y="59"id="value"width="96"/>
<!‐‐RetrievingthevaluefromaSingleton.‐‐><mx:Bu*onlabel="Showthevalue"x="8"y="122"click="retrievedValue.text=getData('myModel',key.text)asString"/><mx:Labelx="135"y="121"width="95"id="retrievedValue"fontWeight="bold"fontSize="15"/><mx:Labelx="10"y="94"fontWeight="bold"fontSize="14"><mx:text>RetrieveanddisplaythevaluefromMyModelbykey</mx:text></fx:DynamicApplicaGon>
SampledynamicapplicaGon(ending)
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ProxyAproxyisanobjectthatrepresentsanotherobjectandcontrolsaccesstoit.
Thinkofasecretarythatreceivesapackageforherboss.
InAcGonScriptyoucanwraptheclassXYZinmx.uGl.ObjectProxy,whichwillbeaproxythatcontrolsaccesstotheXYZ’sproperGes.
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How[Bindable]works?[Bindable]varlastName:String;
Flexcompilergeneratesawrapperclasswithase*erthatdispatchespropertyChangeeventoneachmodificaGonoflastName
Youcandoitonyourownbyusingtheclassmx.uGls.ObjectProxy
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packagecom.farata{publicdynamicclassPerson {publicvarlastName:String="Johnson";publicvarsalary:Number=50000;}}
WrappingPersoninObjectProxy
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RunningthePersonproxy
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ExtendingObjectProxy
AddsomeapplicaGonlogictoit.Ifthesalaryofapersonincreasesover$55K,shebecomesenGtledforthepensionintheamountof2%ofthesalary.YouwanttoaddthisfuncGonalitywithouttouchingthecodeoftheclassPerson.
InasubclassofObjectProxy,youcanoverridegetProperty() andsetProperty() fromthenamespaceflash_proxy.
Ifyou’llwriteMyPersonProxy.lastName=”McCartney”,thisobjectwillcallitsownmethodsetProperty(“lastName”, “McCartney”). InterceptthiscallandaddsomeprocessingtototheoverriddenmethodsetProperty().
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TesGngMyPersonProxy
ACer3clicksaddingpension property
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Mediator
Anycomplexscreen,moreorless,ofabusinessapplicaGonconsistsofanumberofcontainersandcomponents.
Wewanttocreateloosely‐coupledcustomcomponentsthatareselfcontained,donotknowaboutexistenceofeachotherandcancommunicatewiththe“outsideworld”bysendingandreceivingevents.
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BeforethetraderclickedonthePricePanel
ACerthetraderclickedonthePricePanel
WallStreet:StockTradingApplicaGon
PricePanelcomponenthasthreevariables:symbol, bid and ask
PricePaneldispatchestheOrderEventdispatchEvent(new OrderEvent( OrderEvent.PREPARE_ORDER_EVENT, symbol, bid,ask,buy));
OrderPanellistenstoOrderEventaddEventListener(OrderEvent.PLACE_ORDER_EVENT,orderEventHandler)
func5onorderEventHandler(evt:OrderEvent){sym.text=evt.symbol;operaGon.text=evt.buy?"Buy":"Sell";price.text=(oper.text=="Buy"?evt.bid:evt.ask);}
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PricePanelComponent.Take1
OrderEventcarries4variables
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CustomEventOrderEvent
TheMediatorreceivesthiseventfromPricePanelanddispatchesittoOrderPanel
Toomanyuservariables.ItwouldbeagoodideatoencapsulatetheminoneDTO–DataTransferObjecta.k.a.ValueObject
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TheMediatorapplicaGonListentotheOrderEventfromPricingPanel
…andsendittoOrderPanel
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DataTransferObject
DataTransferObjects(DTO)a.k.a.ValueObjects(VO)areusedfordataexchangebetweenvariousapplicaGoncomponents,whichcanbeeitherco‐locatedinthesameprocessoronremotecomputers.
TheseDTO’scanevenbewri*enindifferentprogramminglanguages,forexampleJavaandAcGonScript.
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IntroducingDTOinStockTradingApp.
Insteadofpassingseveralvariablesbetweenpricingandorderpanels,we’llencapsulateorderdetailsintheOrderDTO classandsenditinsidetheeventobjecttothemediator.
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PricePanelComponent.Take2
startDataFeed() emulatesexternaldatafeed
PackagingaDTOinsidetheeventOrderEvent2
UIcomponentsareboundtoDTOproperGes
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NowPricePanelDispatchesOrderEvent2
Theapplica5on(mediator)willgetthiseventanddispatvhittotheOrderPanel:
varorderEvt:OrderEvent2=newOrderEvent2(OrderEvent2.PLACE_ORDER_EVENT,evt.orderInfo);
ordPanel.dispatchEvent(orderEvt); (c)FarataSystems
OrderPanelreceivestheevent…
…extractstheDTOfromtheevent
…andpopulatesUIcomponentsofOrderPanel
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AdvancedDTOs
Ifyouenvisiondynamicupdatestothedataontheclient,declaretheseclassesas[Bindable].
UseanArrayCollecGonofsuchbindableDTO’sasadataProviderinyourDataGrid,List,andsimilarcomponents.
Makesurethatbothserver‐sideandclient‐sideDTOsprovideuniquepropertyuuid.FlexusesthispropertytouniquelyidenGfythedataelementsoftheList‐basedcontrols.
ConsiderreplacingeachpublicproperGeswiththege*erandse*ertohavemorecontroloverthemodificaGonsoftheseproperGes.
Youcanandaddthecodetothesese*ers/ge*ersthatwillintercepttheacGonofdatamodificaGonandperformaddiGonalprocessingbasedonwhat’sbeingchanged.Then,these*ercandispatchtheeventPropertyChangeeventasshownonthenextslide
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SampleDTOwithbidproperty
FarataSystemshascreatedDTOgeneratorforJavaprogrammerscalledDto2FxthatcreatesAcGonScriptDTOsfromtheirJavacounterparts.It’safreeware,andyoucangetitath*p://flexblog.faratasystems.com/?p=357
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AsynchronousToken
TheusermakesseveralRemoteObjectrequestsandresultscomebackasynchronouslyinarbitraryorder.
EachrequestcallsaresulthandlerfuncGonprovidingtheresultevent.
HowtheapplicaGoncodecanmaparrivingresultobjectsbacktotheiniGalrequestors?
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AsyncTokenClassThegoaloftheAsynchronousTokenpa*ernistoproperlyroutetheprocessingontheclientinresponsetothedataarrivingasynchronouslyformtheserver
AsyncTokenisadynamicclass,youcanaddanyproperGestothisclassduringrunGme<mx:RemoteObjectid=”ord”desGnaGon=”Orders”/>…
privatefuncGonsendOrder(/*argumentsgohere*/):void{
vartoken:AsyncToken=ord.placeOrder({item:”SonyTV”});token.orderNumber=”12345”;
token.responder=newResponder(processOrderPlaced,processOrderFault);token.addResponder(newResponder(createShipment,processOrderFault));}
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Whentheresultcomesback
AsyncTokenisalocalobject.ItisidenGfiedbyamessageId thatispassedwiththerequesttoserver.
Whentheserverresponds,itincludesacorrelationId propertyinthemessageheader,andFlexautomaGcallycallstheappropriateAsyncTokenrespondersintheordertheyweredefined.
privatefuncGonprocessOrderPlaced(event:ResultEvent):void{
myOrderNumber:Object=event.token.orderNumber;
//ifmyOrderNumberis12345,processitaccordingly}
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ContactInfo&LinksEmail:[email protected]
Website:h*p://www.faratasystems.com
ClearToolkit:h*p://sourceforge.net/projects/cleartoolkit/
O’ReillyBook“EnterpriseDevelopmentwithFlex”:h*p://my.safaribooksonline.com/9780596801465
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