lexi设计案例分析

1第2章实例研究：Lexi文档编辑器AWYSIWYGdocumenteditor.Mixtextandgraphicsfreelyinvariousformattingstyles.TheusualPull-downmenusScrollbarsPageiconsforjumpingaroundthedocument.通过本实例设计，学习设计模式的实际应用lexi设计案例分析全文共76页，当前为第1页。22.1设计问题Lexi设计的7个问题1文档结构：对文档内部表示的选择几乎影响Lexi设计的每个方面。2格式化3修饰用户界面4支持多种视感标准5支持多种窗口系统6用户操作7拼写检查上述每个问题都有一组相关联的目标集合和限制条件集合。lexi设计案例分析全文共76页，当前为第2页。32.2文档结构目标保持文档的物理结构。即将文本和图形安排到行、列和表等。可视化生成和显示文档。根据显示位置来映射文档内部表示的元素。限制条件应该一致地对待文本和图形。应该一致地对待简单元素和复合元素。但文本分析依赖于被分析对象的类型。lexi设计案例分析全文共76页，当前为第3页。4解决方案：递归组合递归组合：Buildingmorecomplexelementsoutofsimplerones.行——列（段落）——页（P24第2段第2行）第5行第2列的第10个元素

Thetenthelementinlinefiveofcolumntwo,隐含:EachobjecttypeneedsacorrespondingclassAllmusthavecompatibleinterfaces(inheritance)图2包含正文和图形的递归组合图3递归组合的对象结构lexi设计案例分析全文共76页，当前为第4页。5Glyph （图元类）BaseclassforcomposablegraphicalobjectsAnAbstractclassforallobjectsthatcanappearinadocument.Bothprimitiveandcomposed.voidinsert(Glyph)

voidremove(Glyph)

Glyphchild(int)

Glyphparent()管理子图元的接口booleanintersects(Coord,Coord)判断一个指定的点是否与图元相交voiddraw(Window*)VoidBounds（Rect）在窗口上表示自己返回图元占用的矩形面积操作任务基本接口:子类:Character,Image,Space,Row,Columnlexi设计案例分析全文共76页，当前为第5页。6

图元类层次Notetheinherentrecursioninthishierarchyi.e.,aRowisaGlyph&aRowalsohasGlyphs!lexi设计案例分析全文共76页，当前为第6页。7GlyphInterfaceandresponsibilitiesGlyphsknowhowtodrawthemselvesGlyphsknowwhatspacetheyoccupyGlyphsknowtheirchildrenandparentspublicabstractclassGlyph{//appearancepublicabstractvoiddraw(Windoww);publicabstractRectgetBounds();//hitdetectionpublicabstractbooleanintersects(Point);//structurepublicabstractvoidinsert(Glyphg,inti);publicabstractvoidremove(Glyphg);publicabstractGlyphchild(inti);publicabstractGlyphparent();}lexi设计案例分析全文共76页，当前为第7页。8

COMPOSITE

模式objectstructural意图treatindividualobjects&multiple,recursively-composedobjectsuniformly适用objectsmustbecomposedrecursively,andnodistinctionbetweenindividual&composedelements,andobjectsinstructurecanbetreateduniformlyStructurelexi设计案例分析全文共76页，当前为第8页。9COMPOSITE

模式(cont’d)objectstructural效果uniformity:treatcomponentsthesameregardlessofcomplexityextensibility:newComponentsubclassesworkwhereveroldonesdo实现doComponentsknowtheirparents?保持从子部件到父部件的引用能简化组合结构的遍历和管理uniforminterfaceforbothleaves&composites?最大化Component接口don’tallocatestorageforchildreninComponentbaseclassresponsibilityfordeletingchildren由Composite负责删除其子节点lexi设计案例分析全文共76页，当前为第9页。102.3格式化格式化：将一个图元集合分解为若干行目标：自动换行Breakingupadocumentintolines.ManydifferentalgorithmstradeoffqualityforspeedComplexalgorithms限制条件Wanttokeeptheformattingalgorithmwell-encapsulated.independentofthedocumentstructurecanaddformattingalgorithmwithoutmodifyingGlyphscanaddGlyphswithoutmodifyingtheformattingalgorithm.Wanttomakeitdynamicallychangeable.lexi设计案例分析全文共76页，当前为第10页。11Composition&CompositorCompositorbaseclassabstractslinebreakingalgorithmsubclassesforspecializedalgorithms,

e.g.,SimpleCompositor,TeXCompositor接口格式化内容：voidSetComposition（Composition*）格式化：virtualvoidCompose（）Compositioncompositeglyphsuppliedacompositor&leafglyphscreatesrow-columnstructureasdirectedbycompositorlexi设计案例分析全文共76页，当前为第11页。12Composition&Compositor一个未格式化的Composition对象只包含组成文档基本内容的可见图元，它并不包含像行和列这样决定文档物理结构的图元。Composite对象只在刚被创建并以待格式化的图元进行初始化后的状态当Composition对象需要格式化时，调用它的Compositor的Compose操作。Compositor依次遍历Composition的各个图元，根据分行算法插入新的行和列图元。Generatedinaccordancewithcompositorstrategies&donotaffectcontentsofleafglyphslexi设计案例分析全文共76页，当前为第12页。13Compositor&CompositionCompositorclasswillencapsulateaformattingalgorithm.Strategylexi设计案例分析全文共76页，当前为第13页。14Compositor&Composition分行算法封装能增加新的Compositor子类而不触及Glyph类可在运行时刻改变分行算法在Composition接口中增加一个SetCompositor操作lexi设计案例分析全文共76页，当前为第14页。15STRATEGY模式

objectbehavioral意图defineafamilyofalgorithms,encapsulateeachone,&maketheminterchangeabletoletclients&algorithmsvaryindependently适用性whenanobjectshouldbeconfigurablewithoneofmanyalgorithms,andallalgorithmscanbeencapsulated,andoneinterfacecoversallencapsulations结构lexi设计案例分析全文共76页，当前为第15页。16STRATEGY模式(cont’d)objectbehavioral效果greaterflexibility,reusecanchangealgorithmsdynamicallystrategycreation&communicationoverheadinflexibleStrategyinterfacesemanticincompatibilityofmultiplestrategiesusedtogether实现exchanginginformationbetweenaStrategy&itscontextstaticstrategyselectionviatemplateslexi设计案例分析全文共76页，当前为第16页。172.4修饰用户界面Wishtoaddvisiblebordersandscroll-barsaroundpages.Inheritanceisonewaytodoit.leadstoclassproliferationBorderedComposition,ScrollableComposition,BorderedScrollableCompositioninflexibleatrun-timeWillhaveclassesBorderScrollerTheywillbeGlyphstheyarevisibleclientsshouldn’tcareifapagehasaborderornotTheywillbecomposed.butinwhatorder?lexi设计案例分析全文共76页，当前为第17页。182.4修饰用户界面目标:addaframearoundtextcompositionaddscrollingcapability限制条件:embellishmentsshouldbereusablewithoutsubclassing,i.e.,sotheycanbeaddeddynamicallyatruntimeshouldgounnoticedbyclientslexi设计案例分析全文共76页，当前为第18页。19解决方案:“Transparent”Enclosure（透明围栏）Monoglyph：起修饰作用的图元的抽象类baseclassforglyphshavingonechildoperationsonMonoGlyphpassthroughtochildMonoGlyphsubclasses:Frame:addsaborderofspecifiedwidthScroller:scrolls/clipschild,addsscrollbarslexi设计案例分析全文共76页，当前为第19页。20MonoGlyphBordercalls{MonoGlyph.draw();drawBorder();}Decoratorlexi设计案例分析全文共76页，当前为第20页。21TransparentEnclosuresingle-childcompositioncompatibleinterfacesEnclosurewilldelegateoperationstosinglechild,butcanaddstateaugmentbydoingworkbeforeorafterdelegatingtothechild.lexi设计案例分析全文共76页，当前为第21页。22DECORATOR

模式objectstructural意图augmentOneobjectwithnewresponsibilities适用性whenextensionbysubclassingisimpracticalforresponsibilitiesthatcanbewithdrawnStructurelexi设计案例分析全文共76页，当前为第22页。23DECORATOR模式

(cont’d)objectstructural效果responsibilitiescanbeadded/removedatrun-timeavoidssubclassexplosionrecursivenestingallowsmultipleresponsibilities实现interfaceconformanceusealightweight,abstractbaseclassforDecoratorlexi设计案例分析全文共76页，当前为第23页。242.5支持多种视感标准Wanttheapplicationtobeportableacrossdiverseuserinterfacelibraries.EveryuserinterfaceelementwillbeaGlyph.Somewilldelegatetoappropriateplatform-specificoperations.lexi设计案例分析全文共76页，当前为第24页。25MultipleLook&Feels目标:supportmultiplelook&feelstandardsgeneric,Motif,Swing,PM,Macintosh,Windows,...extensibleforfuturestandards限制条件:don’trecodeexistingwidgetsorclientsswitchlook&feelwithoutrecompilinglexi设计案例分析全文共76页，当前为第25页。26解决方案:AbstractObjectCreationInsteadof

Scrollbar*sb=newMotifScrollbar();use

Scrollbar*sb=factory->createScrollbar();wherefactoryisaninstanceofMotifFactorythisbegsthequestionofwhocreatedthefactory!lexi设计案例分析全文共76页，当前为第26页。27FactoryInterfacedefines“manufacturinginterface”subclassesproducespecificproductssubclassinstancechosenatrun-time//ThisclassisessentiallyaJavainterfaceclassFactory{public:Scrollbar*createScrollbar()=0;Menu*createMenu()=0;...};lexi设计案例分析全文共76页，当前为第27页。28ObjectFactoriesUsualmethod:ScrollBarsb=newMotifScrollBar();Factorymethod:ScrollBarsb=guiFactory.createScrollBar();lexi设计案例分析全文共76页，当前为第28页。29ProductObjectsTheoutputofafactoryisaproduct.abstractconcreteAbstractFactorylexi设计案例分析全文共76页，当前为第29页。30BuildingtheFactoryIfknownatcompiletime(e.g.,Lexiv1.0–onlyMotifimplemented).GUIFactoryguiFactory=newMotifFactory();

Setatstartup(Lexiv2.0)StringLandF=appProps.getProperty("LandF");GUIFactoryguiFactory;if(LandF.equals("Motif")) guiFactory=newMotifFactory();...Changeablebyamenucommand(Lexiv3.0)re-initialize‘guiFactory’re-buildtheUISingletonlexi设计案例分析全文共76页，当前为第30页。31ABSTRACTFACTORY

模式objectcreational意图createfamiliesofrelatedobjectswithoutspecifyingclassnames适用性whenclientscannotanticipategroupsofclassestoinstantiateStructurelexi设计案例分析全文共76页，当前为第31页。32ABSTRACTFACTORY模式(cont’d)objectcreational效果flexibility:removestypedependenciesfromclientsabstraction:hidesproduct’scompositionhardtoextendfactoryinterfacetocreatenewproducts实现parameterizationasawayofcontrollinginterfacesizeconfigurationwithPrototypes,i.e.,determineswhocreatesthefactorieslexi设计案例分析全文共76页，当前为第32页。332.6支持多种窗口系统目标:makecompositionappearinawindowsupportmultiplewindowsystems限制条件:minimizewindowsystemdependenciesinapplication&frameworkcodelexi设计案例分析全文共76页，当前为第33页。342.6支持多种窗口系统是否可以用AbstractFactory模式?EachGUIlibrarywilldefineitsownconcreteclasses.无法给每种窗口组件都创建一个公共抽象产品类StartwithanabstractWindowhierarchyuser-levelwindowabstractiondisplaysaglyph(structure)windowsystem-independenttask-relatedsubclasses

(e.g.,IconWindow,PopupWindow)lexi设计案例分析全文共76页，当前为第34页。35classWindow{public:...voidiconify();//window-managementvoidraise();...voiddrawLine(...);//device-independentvoiddrawText(...);//graphicsinterface...};WindowInterfacelexi设计案例分析全文共76页，当前为第35页。36Window实现DefinedinterfaceLexidealswith,butwheredoestherealwindowinglibrarycomeintoit?CoulddefinealternateWindowclasses&subclasses.AtbuildtimecansubstitutetheappropriateoneCouldsubclasstheWindowhierarchy.Bridgelexi设计案例分析全文共76页，当前为第36页。37Window实现代码示例publicclassRectangleextendsGlyph{publicvoiddraw(Windoww){w.drawRect(x0,y0,x1,y1);}...}publicclassWindow{publicvoiddrawRect(Coordx0,y0,x1,y1){imp.drawRect(x0,y0,x1,y1);}...}publicclassXWindowImpextendsWindowImp{publicvoiddrawRect(Coordx0,y0,x1,y1){...XDrawRectangle(display,windowId,graphics,x,y,w,h);}}lexi设计案例分析全文共76页，当前为第37页。38配置‘imp’publicabstractclassWindowSystemFactory{publicabstractWindowImpcreateWindowImp();publicabstractColorImpcreateColorImp();...}publicclassXWindowSystemFactoryextendsWindowSystemFactory{publicWIndowImpcreateWindowImp(){returnnewXWindowImp();}...}publicclassWindow{Window(){imp=windowSystemFactory.createWindowImp();}...}AbstractFactorywell-knownobjectlexi设计案例分析全文共76页，当前为第38页。39对象结构

Note：thedecouplingbetweenthelogicalstructureofthecontentsinawindowfromthephysicalrenderingofthecontentsinthewindowlexi设计案例分析全文共76页，当前为第39页。40BRIDGE模式

objectstructural意图separatea(logical)abstractioninterfacefromits(physical)implementation(s)适用性wheninterface&implementationshouldvaryindependentlyrequireauniforminterfacetointerchangeableclasshierarchiesStructurelexi设计案例分析全文共76页，当前为第40页。41BRIDGE模式(cont’d)objectstructural效果abstractioninterface&implementationareindependentimplementationscanvarydynamicallyone-size-fits-allAbstraction&Implementorinterfaces实现sharingImplementors&referencecountingcreatingtherightimplementorlexi设计案例分析全文共76页，当前为第41页。422.7用户操作Operationscreatenew,save,cut,paste,quit,…UImechanismsmousing&typinginthedocumentpull-downmenus,pop-upmenus,buttons,kbdaccelerators,…Wishtode-coupleoperationsfromUImechanismre-usesamemechanismformanyoperationsre-usesameoperationbymanymechanismsOperationshavemanydifferentclasseswishtode-coupleknowledgeoftheseclassesfromtheUIWishtosupportmulti-levelundoandredolexi设计案例分析全文共76页，当前为第42页。43CommandsAbuttonorapull-downmenuisjustaGlyph.buthaveactionscommandassociatedwithuserinpute.g.,MenuItemextendsGlyph,ButtonextendsGlyph,…Could…PageFwdMenuItemextendsMenuItemPageFwdButtonextendsButtonCould…HaveaMenuItemattributewhichisafunctioncall.没有强调撤销/重做操作很难将状态和函数联系起来函数很难扩充，并且很难部分复用。Will…HaveaMenuItemattributewhichisacommandobject.lexi设计案例分析全文共76页，当前为第43页。44Command:EncapsulateEachRequest

ACommandencapsulatesCommandmayimplementtheoperationsitself,ordelegatethemtootherobject(s)anoperation(execute())aninverseoperation(unexecute())aoperationfortestingreversibility

(boolean

reversible())statefor(un)doingtheoperationlexi设计案例分析全文共76页，当前为第44页。45Command类层次Commandisanabstractclassforissuingrequests.lexi设计案例分析全文共76页，当前为第45页。46MenuItem与Command之间的关系voidMenuItem::clicked(){

command->execute();

}voidPasteCommand::execute(){

//dothepaste

}voidCopyCommand::execute(){

//dothecopy

}lexi设计案例分析全文共76页，当前为第46页。47InvokingCommandsWhenaninteractiveGlyphistickled,itcallstheCommandobjectwithwhichithasbeeninitialized.Commandlexi设计案例分析全文共76页，当前为第47页。48Undo/RedoAddanunexecute()methodtoCommandReversestheeffectsofaprecedingexecute()operationusingwhateverundoinformationexecute()storedintotheCommandobject.AddaisUndoable()andahadnoEffect()methodMaintainCommandhistory:lexi设计案例分析全文共76页，当前为第48页。49COMMAND模式

objectbehavioral意图encapsulatetherequestforaservice适用性toparameterizeobjectswithanactiontoperformformultilevelundo/redoStructurelexi设计案例分析全文共76页，当前为第49页。50COMMAND模式(cont’d)objectbehavioral效果abstractsexecutorofaservicesupportsarbitrary-levelundo-redocompositionyieldsmacro-commandsmightresultinlotsoftrivialcommandsubclasseslexi设计案例分析全文共76页，当前为第50页。512.8拼写检查和断字处理Textualanalysischeckingformisspellingsintroducinghyphenationpointswhereneededforgoodformatting.Wanttosupportmultiplealgorithms.Wanttomakeiteasytoaddnewalgorithms.WanttomakeiteasytoaddnewtypesoftextualanalysiswordcountgrammarLegibility(易读性）Wishtode-coupletextualanalysisfromtheGlyphclasses.lexi设计案例分析全文共76页，当前为第51页。522.8拼写检查和断字处理目标:analyzetextforspellingerrorsintroducepotentialhyphenation（断字）sites限制条件:supportmultiplealgorithmsdon’ttightlycouplealgorithmswithdocumentstructurelexi设计案例分析全文共76页，当前为第52页。53AccessingScatteredInformationNeedtoaccessthetextletter-by-letter.OurdesignhastextscatteredallovertheGlyphhierarchy.DifferentGlyphshavedifferentdatastructuresforstoringtheirchildren(lists,trees,arrays,…).Sometimesneedalternateaccesspatterns:spellcheck:forwardsearchback:backwardsevaluatingequations:inordertreetraversallexi设计案例分析全文共76页，当前为第53页。54EncapsulatingAccess&TraversalsCouldreplaceindex-orientedaccess(asshownbefore)bymoregeneralaccessorsthataren’tbiasedtowardsarrays.Glyphg=…for(g.first(PREORDER);!g.done();g->next()){Glyphcurrent=g->getCurrent();…}Problems:can’tsupportnewtraversalswithoutextendingenumandmodifyingallparentGlyphtypes.Can’tre-usecodetotraverseotherobjectstructures(e.g.,Commandhistory).lexi设计案例分析全文共76页，当前为第54页。55解决方案:封装遍历IteratorencapsulatesatraversalalgorithmwithoutexposingrepresentationdetailstocallersusesGlyph’schildenumerationoperationThisisanexampleofa“preorderiterator”lexi设计案例分析全文共76页，当前为第55页。56Iterator层次Iteratorlexi设计案例分析全文共76页，当前为第56页。57UsingIteratorsGlyph*g;Iterator<Glyph*>*i=g->CreateIterator();for(i->First();!i->IsDone();i->Next()){Glyph*child=i->CurrentItem();//dosomethingwithcurrentchild}lexi设计案例分析全文共76页，当前为第57页。58InitializingIteratorsIterator<Glyph*>*Row::CreateIterator(){returnnewListIterator<Glyph*>(_children);}lexi设计案例分析全文共76页，当前为第58页。59ImplementingaComplexIteratorvoidPreorderIterator::First(){Iterator<Glyph*>*i=_root->CreateIterator();if(i){i->First();_iterators.RemoveAll();_iterators.Push(i);}}Glyph*PreorderIterator::CurrentItem()const{return_iterators.Size()>0?_iterators.Top()->CurrentItem():0;}lexi设计案例分析全文共76页，当前为第59页。60ImplementingaComplexIterator(cont’d)voidPreorderIterator::Next(){Iterator<Glyph*>*i=_iterators.Top()->CurrentItem()->CreateIterator();i->First();_iterators.Push(i);while(_iterators.Size()>0&&_iterators.Top()->IsDone()){delete_iterators.Pop();_iterators.Top()->Next();}}lexi设计案例分析全文共76页，当前为第60页。61ITERATOR模式

objectbehavioral意图accesselementsofacontainerwithoutexposingitsrepresentation适用性requiremultipletraversalalgorithmsoveracontainerrequireauniformtraversalinterfaceoverdifferentcontainerswhencontainerclasses&traversalalgorithmmustvaryindependentlyStructurelexi设计案例分析全文共76页，当前为第61页。62ITERATOR模式

(cont’d)objectbehavioral效果flexibility:aggregate&traversalareindependentmultipleiterators&multipletraversalalgorithmsadditionalcommunicationoverheadbetweeniterator&aggregate实现internalversusexternaliteratorsviolatingtheobjectstructure’sencapsulationrobustiteratorslexi设计案例分析全文共76页，当前为第62页。63ITERATOR

模式(cont’d)objectbehavioralintmain(intargc,char*argv[]){vector<string>args;for(inti=0;i<argc;i++) args.push_back(string(argv[i]));for(vector<string>::iteratori(args.begin());i!=args.end();i++)cout<<*i;cout<<endl;return0;}IteratorsareusedheavilyintheC++StandardTemplateLibrary(STL)ThesameiteratorpatterncanbeappliedtoanySTLcontainer!lexi设计案例分析全文共76页，当前为第63页。64访问动作Nowthatwecantraverse,weneedtoaddactionswhiletraversingthathavestatespelling,hyphenation,…CouldaugmenttheIteratorclasses……butthatwouldreducetheirreusabilityCouldaugmenttheGlyphclasses……butwillneedtochangeGlyphclassesforeachnewanalysisWillneedtoencapsulatetheanalysisinaseparateobjectlexi设计案例分析全文共76页，当前为第64页。65Visitordefinesaction(s)ateachstepoftraversalavoidswiringaction(s)intoGlyphsiteratorcallsglyph’saccept(Visitor)ateachnodeaccept()callsbackonvisitor(aformof“staticpolymorphism”basedonmethodoverloadingbytype)voidCharacter::accept(Visitor&v){v.visit(*this);}classVisitor{public:virtualvoidvisit(Character&);virtualvoidvisit(Rectangle&);virtualvoidvisit(Row&);//etc.forallrelevantGlyphsubclasses

};lexi设计案例分析全文共76页，当前为第65页。66ActionsinIteratorsIteratorwillcarrytheanalysisobjectalongwithitasititerates.Theanalyzerwillaccumulatestate.e.g.,charactersforaspellchecklexi设计案例分析全文共76页，当前为第66页。67AvoidingDowncastsHowcantheanalysisobjectdistinguishdifferentkindsofGlyphswithoutresortingtoswitchstatementsanddowncasts.e.g.,avoid:publicclassSpellingCheckerextends…{publicvoidcheck(Glyphg){if(ginstanceofCharacterGlyph){CharacterGlyphcg=(CharacterGlyph)g;//analyzethecharacter}elseif(ginstanceofRowGlyph){rowGlyphrg=(RowGlyph)g;//preparetoanalyzethechildglyphs}else…}}lexi设计案例分析全文共76页，当前为第67页。68AcceptingVisitorspublicabstractclassGlyph{publicabstractvoidaccept(Visitorv);…}publicclassCharacterGlyphextendsGlyph{publicvoidaccept(Visitorv){v.visitCharacterGlyph(this);}…}lexi设计案例分析全文共76页，当前为第68页。69Visitor&SubclassespublicabstractclassVisitor{publicvoidvisitCharacterGlyph(CharacterGlyphcg){/*donothing*/}publicabstractvoidvisitRowGlyph(RowGlyphrg);{/*donothing*/}…}publicclassSpellingVisitorextendsVisitor{publicvoidvisitCharacterGlyph(CharacterGlyphcg){…}}Visitorlexi设计案例分析全文共76页，当前为第69页。70SpellingVisitorpublicclassSpellingVisitorextendsVisitor{privateVectormisspellings=newVector();privateStringcurrentWord=“”;publicvoidvisitCharacterGlyph(CharacterGlyphcg){charc=cg->get