As mentioned throughout this document, the Presentation Manager application model promotes the reuse of application objects, by facilitating code modularity through data abstraction and encapsulation. With correct design procedures, it is possible to create generic application objects that may be used by multiple applications. Should subsequent applications require modification to allow different processing of particular message classes, this may be achieved through subclassing. The Workplace Shell application model introduced in OS/2 Version 2.0 provides even more potential for reuse, due to its enhanced support of inheritance and subsequently enhanced provision for object reuse.
Standardization and reuse of application code promotes consistency between applications in terms of processing techniques and user interfaces, and helps to enforce organizational programming and interface design standards. It also reduces the amount of new code required for applications, potentially shortening development time, and the use of previously developed and tested code may also decrease application testing time.
In situations where reusability at the application object level is either not possible or impractical, common application functions may still be developed as subroutines, and placed in libraries for access by multiple applications. The use of such subroutines reduces application development time.
This chapter examines the creation of such generic objects and subroutines within the Presentation Manager application model, and their placement in dynamic link libraries for subsequent use by applications. Since Workplace Shell objects are by definition placed in DLLs and available for reuse, they are not explicitly discussed in this chapter.