lexi设计案例分析.pptx

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1、lexi设计设计案例分析案例分析2.1 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。2.2 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。解决方案：递归组合递归组合：Building more complex element

2、s out of simpler ones.行列（段落）页（P24 第2段第2行）第5行第2列的第10个元素 The tenth element in line five of column two,隐含:Each object type needs a corresponding classAll must have compatible interfaces(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Glyph（图元类）Base class for composable graphical objectsAn Abstract class for all

3、 objects that can appear in a document.Both primitive and composed.void insert(Glyph)void remove(Glyph)Glyph child(int)Glyph parent()管理子图元的接口boolean intersects(Coord,Coord)判断一个指定的点是否与图元相交void draw(Window*)Void Bounds（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,Column 图元类层次Note the

4、inherent recursion in this hierarchywi.e.,a Row is a Glyph&a Row also has Glyphs!Glyph Interface and responsibilitiesGlyphs know how to draw themselvesGlyphs know what space they occupyGlyphs know their children and parentspublic abstract class Glyph /appearance public abstract void draw(Window w);p

5、ublic abstract Rect getBounds();/hit detection public abstract boolean intersects(Point);/structure public abstract void insert(Glyph g,int i);public abstract void remove(Glyph g);public abstract Glyph child(int i);public abstract Glyph parent();COMPOSITE 模式 object structural意图treat individual objec

6、ts&multiple,recursively-composed objects uniformly适用objects must be composed recursively,and no distinction between individual&composed elements,and objects in structure can be treated uniformlyStructureCOMPOSITE 模式(contd)object structural效果+uniformity:treat components the same regardless of complex

7、ity+extensibility:new Component subclasses work wherever old ones do实现do Components know their parents?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uniform interface for both leaves&composites?最大化Component接口dont allocate storage for children in Component base classresponsibility for deleting children由Composite负责删除其子节点

8、2.3 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Breaking up a document into lines.Many different algorithmstrade off quality for speedComplex algorithms限制条件Want to keep the formatting algorithm well-encapsulated.independent of the document structurecan add formatting algorithm without modifying Glyphscan add Glyphs

9、without modifying the formatting algorithm.Want to make it dynamically changeable.Composition&CompositorCompositorbase class abstracts linebreaking algorithmsubclasses for specialized algorithms,e.g.,SimpleCompositor,TeXCompositor接口接口格式化内容：格式化内容：void SetComposition（Composition*）格式化：格式化：virtual void

10、Compose（）（）Compositioncomposite glyphsupplied a compositor&leaf glyphscreates row-column structure as directed by compositorComposition&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

11、历Composition的各个图元，根据分行算法插入新的行和列图元。Generated in accordance with compositor strategies&do not affect contents of leaf glyphsCompositor&CompositionCompositor class will encapsulate a formatting algorithm.Compositor&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

12、操作STRATEGY模式 object behavioral意图define a family of algorithms,encapsulate each one,&make them interchangeable to let clients&algorithms vary independently适用性when an object should be configurable with one of many algorithms,and all algorithms can be encapsulated,and one interface covers all encapsula

13、tions 结构STRATEGY模式(contd)object behavioral效果+greater flexibility,reuse+can change algorithms dynamicallystrategy creation&communication overheadinflexible Strategy interfacesemantic incompatibility of multiple strategies used together实现exchanging information between a Strategy&its contextstatic stra

14、tegy selection via templates2.4 修饰用户界面Wish to add visible borders and scroll-bars around pages.Inheritance is one way to do it.leads to class proliferationBorderedComposition,ScrollableComposition,BorderedScrollableCompositioninflexible at run-timeWill have classesBorderScrollerThey will be Glyphsth

15、ey are visibleclients shouldnt care if a page has a border or notThey will be composed.but in what order?2.4 修饰用户界面目标:add a frame around text compositionadd scrolling capability限制条件:embellishments should be reusable without subclassing,i.e.,so they can be added dynamically at runtimeshould go unnoti

16、ced by clients解决方案:“Transparent”Enclosure（透明围栏）Monoglyph：起修饰作用的图元的抽象类：起修饰作用的图元的抽象类base class for glyphs having one childoperations on MonoGlyph pass through to childMonoGlyph subclasses:Frame:adds a border of specified widthScroller:scrolls/clips child,adds scrollbarsMonoGlyphBorder calls MonoGlyph.

17、draw();drawBorder();Transparent Enclosuresingle-child compositioncompatible interfacesEnclosure will delegate operations to single child,but canadd stateaugment by doing work before or after delegating to the child.DECORATOR 模式 object structural意图augment One object with new responsibilities适用性when e

18、xtension by subclassing is impracticalfor responsibilities that can be withdrawnStructureDECORATOR模式(contd)object structural效果+responsibilities can be added/removed at run-time+avoids subclass explosion+recursive nesting allows multiple responsibilities实现interface conformanceuse a lightweight,abstra

19、ct base class for Decorator2.5 支持多种视感标准Want the application to be portable across diverse user interface libraries.Every user interface element will be a Glyph.Some will delegate to appropriate platform-specific operations.Multiple Look&Feels目标:support multiple look&feel standardsgeneric,Motif,Swing

20、,PM,Macintosh,Windows,.extensible for future standards限制条件:dont recode existing widgets or clientsswitch look&feel without recompiling解决方案:Abstract Object CreationInstead ofScrollbar*sb=new MotifScrollbar();useScrollbar*sb=factory-createScrollbar();where factory is an instance of MotifFactorythis be

21、gs the question of who created the factory!Factory Interfacedefines“manufacturing interface”subclasses produce specific productssubclass instance chosen at run-time/This class is essentially a Java interfaceclass Factory public:Scrollbar*createScrollbar()=0;Menu*createMenu()=0;.;Object FactoriesUsua

22、l method:ScrollBar sb=new MotifScrollBar();Factory method:ScrollBar sb=guiFactory.createScrollBar();Product ObjectsThe output of a factory is a product.abstractconcreteBuilding the FactoryIf known at compile time(e.g.,Lexi v1.0 only Motif implemented).GUIFactory guiFactory=new MotifFactory();Set at

23、startup(Lexi v2.0)String LandF=appProps.getProperty(LandF);GUIFactory guiFactory;if(LandF.equals(Motif)guiFactory=new MotifFactory();.Changeable by a menu command(Lexi v3.0)re-initialize guiFactoryre-build the UIABSTRACT FACTORY 模式 object creational意图create families of related objects without specif

24、ying class names适用性when clients cannot anticipate groups of classes to instantiateStructureABSTRACT FACTORY模式(contd)object creational效果+flexibility:removes type dependencies from clients+abstraction:hides products compositionhard to extend factory interface to create new products实现parameterization a

25、s a way of controlling interface sizeconfiguration with Prototypes,i.e.,determines who creates the factories2.6 支持多种窗口系统目标:make composition appear in a windowsupport multiple window systems限制条件:minimize window system dependencies in application&framework code2.6 支持多种窗口系统是否可以用 Abstract Factory模式?Each

26、 GUI library will define its own concrete classes.无法给每种窗口组件都创建一个公共抽象产品类Start with an abstract Window hierarchyuser-level window abstractiondisplays a glyph(structure)window system-independenttask-related subclasses(e.g.,IconWindow,PopupWindow)class Window public:.void iconify();/window-management vo

27、id raise();.void drawLine(.);/device-independent void drawText(.);/graphics interface .;Window InterfaceWindow 实现Defined interface Lexi deals with,but where does the real windowing library come into it?Could define alternate Window classes&subclasses.At build time can substitute the appropriate oneC

28、ould subclass the Window hierarchy.Window 实现代码示例public class Rectangle extends Glyph public void draw(Window w)w.drawRect(x0,y0,x1,y1);.public class Window public void drawRect(Coord x0,y0,x1,y1)imp.drawRect(x0,y0,x1,y1);.public class XWindowImp extends WindowImp public void drawRect(Coord x0,y0,x1,

29、y1).XDrawRectangle(display,windowId,graphics,x,y,w,h);配置 imp public abstract class WindowSystemFactory public abstract WindowImp createWindowImp();public abstract ColorImp createColorImp();.public class XWindowSystemFactory extends WindowSystemFactory public WIndowImp createWindowImp()return new XWi

30、ndowImp();.public class Window Window()imp=windowSystemFactory.createWindowImp();.well-known object对象结构Note：the decoupling between the logical structure of the contents in a window from the physical rendering of the contents in the windowBRIDGE 模式 object structural意图separate a(logical)abstraction in

31、terface from its(physical)implementation(s)适用性when interface&implementation should vary independentlyrequire a uniform interface to interchangeable class hierarchiesStructureBRIDGE 模式(contd)object structural效果+abstraction interface&implementation are independent+implementations can vary dynamicallyo

32、ne-size-fits-all Abstraction&Implementor interfaces实现sharing Implementors&reference countingcreating the right implementor2.7 用户操作Operationscreate new,save,cut,paste,quit,UI mechanismsmousing&typing in the documentpull-down menus,pop-up menus,buttons,kbd accelerators,Wish to de-couple operations fro

33、m UI mechanismre-use same mechanism for many operationsre-use same operation by many mechanismsOperations have many different classeswish to de-couple knowledge of these classes from the UIWish to support multi-level undo and redoCommandsA button or a pull-down menu is just a Glyph.but have actions

34、command associated with user inpute.g.,MenuItem extends Glyph,Button extends Glyph,CouldPageFwdMenuItem extends MenuItemPageFwdButton extends ButtonCouldHave a MenuItem attribute which is a function call.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。WillHave a MenuItem attribute which is a command object.C

35、ommand:Encapsulate Each RequestA Command encapsulatesCommand maynimplement the operations itself,orndelegate them to other object(s)nan operation(execute()nan inverse operation(unexecute()na operation for testing reversibility(boolean reversible()nstate for(un)doing the operationCommand 类层次Command i

36、s an abstract class for issuing requests.MenuItem与Command 之间的关系void MenuItem:clicked()command-execute();void PasteCommand:execute()/do the pastevoid CopyCommand:execute()/do the copyInvoking CommandsWhen an interactive Glyph is tickled,it calls the Command object with which it has been initialized.U

37、ndo/RedoAdd an unexecute()method to CommandReverses the effects of a preceding execute()operation using whatever undo information execute()stored into the Command object.Add a isUndoable()and a hadnoEffect()methodMaintain Command history:COMMAND模式 object behavioral意图encapsulate the request for a ser

38、vice适用性to parameterize objects with an action to performfor multilevel undo/redoStructureCOMMAND模式(contd)object behavioral效果+abstracts executor of a service+supports arbitrary-level undo-redo+composition yields macro-commandsmight result in lots of trivial command subclasses2.8 拼写检查和断字处理Textual anal

39、ysischecking for misspellingsintroducing hyphenation points where needed for good formatting.Want to support multiple algorithms.Want to make it easy to add new algorithms.Want to make it easy to add new types of textual analysisword countgrammarLegibility(易读性）Wish to de-couple textual analysis from

40、 the Glyph classes.2.8 拼写检查和断字处理目标:analyze text for spelling errorsintroduce potential hyphenation（断字）sites限制条件:support multiple algorithmsdont tightly couple algorithms with document structureAccessing Scattered InformationNeed to access the text letter-by-letter.Our design has text scattered all o

41、ver the Glyph hierarchy.Different Glyphs have different data structures for storing their children(lists,trees,arrays,).Sometimes need alternate access patterns:spell check:forwardsearch back:backwardsevaluating equations:inorder tree traversalEncapsulating Access&TraversalsCould replace index-orien

42、ted access(as shown before)by more general accessors that arent biased towards arrays.Glyph g=for(g.first(PREORDER);!g.done();g-next()Glyph current=g-getCurrent();Problems:cant support new traversals without extending enum and modifying all parent Glyph types.Cant re-use code to traverse other objec

43、t structures(e.g.,Command history).解决方案:封装遍历Iteratorencapsulates a traversal algorithm without exposing representation details to callers uses Glyphs child enumeration operationThis is an example of a“preorder iterator”Iterator 层次Using IteratorsGlyph*g;Iterator*i=g-CreateIterator();for(i-First();!i-

44、IsDone();i-Next()Glyph*child=i-CurrentItem();/do something with current child Initializing IteratorsIterator*Row:CreateIterator()return new ListIterator(_children);Implementing a Complex Iteratorvoid PreorderIterator:First()Iterator*i=_root-CreateIterator();if(i)i-First();_iterators.RemoveAll();_ite

45、rators.Push(i);Glyph*PreorderIterator:CurrentItem()const return _iterators.Size()0?_iterators.Top()-CurrentItem():0;Implementing a Complex Iterator(contd)void PreorderIterator:Next()Iterator*i=_iterators.Top()-CurrentItem()-CreateIterator();i-First();_iterators.Push(i);while(_iterators.Size()0&_iter

46、ators.Top()-IsDone()delete _iterators.Pop();_iterators.Top()-Next();ITERATOR模式 object behavioral意图access elements of a container without exposing its representation适用性require multiple traversal algorithms over a containerrequire a uniform traversal interface over different containerswhen container c

47、lasses&traversal algorithm must vary independentlyStructureITERATOR模式(contd)object behavioral效果+flexibility:aggregate&traversal are independent+multiple iterators&multiple traversal algorithmsadditional communication overhead between iterator&aggregate实现internal versus external iteratorsviolating th

48、e object structures encapsulationrobust iteratorsITERATOR 模式(contd)object behavioralint main(int argc,char*argv)vector args;for(int i=0;i argc;i+)args.push_back(string(argvi);for(vector:iterator i(args.begin();i!=args.end();i+)cout *i;cout getChar();if(isalpha(c)currentWord+=c;else if(isMispelled(cu

49、rrentWord)/add misspelling to list misspelling.addElement(currentWord);currentWord=“”;public Vector getMisspellings return misspellings;Using SpellingVisitorPreorderIterator i=new PreorderIterator();i.setVisitor(new SpellingVisitor();i.visitAll(rootGlyph);Vector misspellings=(SpellingVisitor)i.getVi

50、sistor().getMisspellings();public class Iterator private Visitor v;public void visitAll(Glyph start)for(first();!isDone();next()currentItem().visit(v);CharacterGlyph(a)CharacterGlyph(_)spell:SpellingVisitorVisitor Activity Diagramvisit(spell)visitCharacterGlyph(this)getChar()visitCharacterGlyph(this