- Objects are represented by their properties and methods, and are instances of classes. A class defines a set of objects. - In PowerBuilder, classes are defined using painters like the Application, Menu, User Object, and Window painters. Class definitions are stored in libraries like PBLs, PBDs, DLLs and EXEs. - Properties and methods can be added to classes. Properties are added as instance variables, while methods include events, functions, and external functions. Common types of methods that can be added are events, object functions, and external functions.

1. Buliding Object-Oriented Applications in PowerBuilder Module 2: Objects And Classes

2. Objectives Define Object and Classes Use Edit Source (system tree) / Export Syntax (Iibrary painter) to view the definition of classes Add Properties and Methods to a class

3. Topics: Objects and Classes Definitions Defining Classes Viewing Class Definitions What Can Be Added to a Class Adding Properties to a Class Adding Methods to a Class

4. Objects — Definition An object is represented by its: Properties: Visible, color, height Property values (data): George, red, 5'8" Methods (behaviors): Pitches a baseball, eats anchovy pizza

5. Classes — Definition A class defines a set of objects Each object is an instance of its class Class Definition Object Instance

6. Defining Classes Done in Painters Window Menu User-Object Application Based on Inheritance

7. New Objects Created Through Inheritance

8. Defining Classes Stored in PBLs, PBDs, DLLs, and EXEs

9. Syntax — Window Subclass of window class Class properties changed

10. Defining Classes User-defined classes of applications, menus, user objects, and windows can: Have new properties (instance variables) Have new methods (events, object functions, and local external functions)

11. Adding Properties — Instance Variables

12. Methods of a Class Methods are object behaviors Represented by scripts associated with: Events Functions

13. System Methods Mapped to specific event ids. You cannot add / change arguments Show/Hide Prototype Cannot Modify Arguments

14. Adding Methods — Events An event is a notification that an action has occurred System events are operating system or PowerBuilder events Examples: Clicked, Open, Constructor, RButtonDown, RetrieveStart, DBError User-defined events can be: Added to windows, user objects, and window controls Mapped to system events or unmapped

15. User-Defined Events

16. Mapped Events Predefined events Dependent on operating system ue_downkey ---> pbm_dwnkey Arguments and return data type are predefined

17. Unmapped Events An unmapped event: Is independent of system and PowerBuilder events Is invoked via scripts only Supports user-defined arguments and a user-specified return data type

18. User-Defined Events Mapped or Unmapped Events Determined

19. Adding Methods — Functions Built-in functions: System (Global) functions Class functions User-defined functions: Object functions External functions

20. Adding Methods — Object Functions Functions defined for a class are methods A function definition consists of: Name Return data type (optional) Arguments and their data types (optional) Script (optional) Access privilege Can be defined for Application, Menu, Window, and UserObject classes

21. Adding Functions

22. Adding Functions

23. Adding Methods — External Functions Reside in DLLs or EXEs Created outside of PowerBuilder (for example, using C++) Must be declared to PowerBuilder Can be called as any other function Can be global or local Can be defined at the object level for menus, user objects, and windows

24. Adding Methods — External Functions

25. Summary Events Yes (v8) Yes (v8) Yes Yes Yes Class Application Menu UserObject Window Window control Instance Variables Yes Yes Yes Yes No Object Function Yes Yes Yes Yes No External Function No Yes Yes Yes No

26. Summary A class has a name, properties, and methods. A class is the definition of a set of objects. An object is an instance of a class. The four main PowerBuilder painters are: Application, Menu, User Object, and Window. PowerBuilder class definitions are stored in libraries: PBLs for development PBDs, DLLs and EXEs for an executable

27. Summary Questions

28. Lab Setup What you will need to do the lab: Set the application search path Connect to the Database Add properties to a class as instance variables Add function methods to a class Preview a window

29. Lab Debriefing Created two instance variables: is_action and il_key

30. Lab Debriefing Created two methods to set properties

31. Lab Debriefing Created two methods to get properties

32. Lab Debriefing But we have not fully encapsulated these properties. (more in later chapters) Can you access these properties using direct access? Should you? But can you? What are some disadvantages of not fully encapsulating these?