Mastering PowerBuilder

Strategy #3: Insert a layer between PFC and PFE

The objects in the PFE level are at the lowest level of extension. When PFC creates and instantiates an object its' datatype is an object in the PFE level. When additional extension levels are inserted between PFC and PFE the attributes and methods added to objects in these inserted extensions levels will be available to PFC. For Example, when the of_SetError() function is called in an application to turn on the error service a instance reference variable is created:

n_cst_error inv_error inv_error = CREATE n_cst_error

To extend existing PFC services in CORP layer:

• Inherit service objects from PFC level and save in CORP level
• Modify service objects, add methods (instance variables, functions, events etc. ...)
• Inherit service objects from CORP level and save in PFE level
• Regenerate hierarchy of objects.

If there are no services/variables to be added/modified, then there is no reason to add an additional layer in the inheritance hierarchy.

This is the most flexible and powerful method to add a corporate framework layer. You need to insert corporate layer between PFC and PFE, meaning objects in PFE inherit from corporate layer objects. That means, you can use PFE as application layer or you can append application specific layer to PFE.

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