Design Patterns

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ADVANTAGES OF DESIGN PATTERNS (TICHY) • Improvement of team communication Design pattern as “short formula” in discussions • Compilation of essential concepts, expressed in a concrete form • Documentation of the “state of the art” Help for less experienced designers, not constantly reinventing the wheel • Improvement of the code quality Given structure, code examples DESCRIPTION OF DESIGN PATTERNS (GOF) (2) Collaborations How do the participants collaborate to carry out their responsibilities? Consequences What are the trade-offs and results of using the pattern? What aspect of system structure does it let one vary independently? Implementation What pitfalls, hints, or techniques should one be aware of 21 when implementing the pattern? Are there any language-specific issues? Sample Code Code fragments in C ++ or Smalltalk. Known Uses At least two examples of applications taken from existing systems of different fields. Related Patterns Similar patterns and patterns that are often used in combination with the described pattern. 23 DESCRIPTION OF DESIGN PATTERNS (GOF) (1) Name and Classification A good name is important, because it will become part of the design vocabulary. Intent What does the pattern do? Which problems does it solve? Also Known As Other familiar names. Motivation Scenario which illustrates the design problem and how the pattern solves the problem. Applicability What are the situations in which the design pattern can be applied? How can one recognize these situations? Structure Class and interaction diagrams. Participants Classes and objects, which are part of the pattern, as well as their responsibilities. MODEL-VIEW-CONTROLLER (MVC) • Architectural Style a /Design Pattern b -Hybrid • aggregate design pattern out of – Composite – Observer – Strategy – Factory Method 22 • Clear distinction of data (model), data representation on a screen (view) and control of data manipulation or views (controller) a Buschmann et al. – Pattern-Oriented Software Architecture – A System of Patterns, John Wiley & Sons, 1996. b GoF 24
HOW MVC WORKS – AN OVERVIEW MVC CLASS DIAGRAM call update Model coreData setOfObservers attach(Observer) detach(Observer) notify getData service View(s) Model attach getData View 25 myModel myController initialize(Model) makeController activate display update create manipulate display attach call service Observer update User Controller Controller myModel myView initialize(Model,View) handleEvent update • Model: does not know View or Controller beforehand, announces change by calling update, related components request model state by getData, if needed keep data in a data base • View: connected to Model, displays data (visually, acoustically, or similar) normally on a screen • Controller: administrates Views, manipulates data on behalf of the user, ”brain” of the application 27 DESCRIPTION OF MVC, TRYGVE M. H. REENSKAUG Intent Interactive applications with a flexible human-computer interface. Motivation Adaptability and Reuse Participants MVC seperates the application into three (independent) components • Model offers core functionality a and data • View provides information to the user • Controller handles user input • All three components are related by a change-propagation mechanism. • View and Controller constitute the user interface. a stable, because it is related to requirements 26 Design Patterns of MVC in detail 28
Page 1 and 2: Design Patterns DESIGN PATTERNS: CH
Page 3 and 4: ASSOCIATIONS ➠ denote the relatio
Page 5: Classifying, Describing, and Using
Page 9 and 10: • Composite (picture) - defines b
Page 11 and 12: Known Uses • View-class in Model/
Page 13 and 14: Participants • Subject - knows it
Page 15 and 16: APPLICATION OF THE STRATEGY PATTERN
Page 17: ➠ We have presented and used the

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