Fundamentals of object sharing in Oracle Forms 10g

This article is all about the fundamentals of sharing the objects in Oracle Forms , its benefits and the various ways to do it. It will describes the various methods for reusing objects – Property Classes, Copying and Subclassing Objects and Code, Object Groups, Object Libraries and  SmartClasses.

When you share and reuse objects and code, you increase productivity, decrease maintenance, increase modularity, and improve the performance of your applications. When you are developing applications, you should share and reuse objects and code wherever possible.

There are many advantages of sharing and reusing objects and code.

To maximize reuse, the developer should apply the following guidelines in the order shown:

 Now lets discuss the various methods of object sharing:

A property class is a named object that contains a list of properties and their settings. You can use property classes to increase productivity and improve network performance.

 Here are some of the uses of a property class:

 Note: Once an item is defined, the meta-data about the next item includes only those properties that differ from the previous item. This is referred to as message diffing.

When you create a property class, you have all the properties from every Forms Builder object available. You choose the properties and their values to include in the property class. You can create a property class in two ways:

Once you create a property class and add properties, you can use the property class. To apply the properties from a property class to an object, use the Subclass Information property in the Property Palette.

An inherited property is one that takes its value from the property class that you associated with the object. An inherited property is displayed with an arrow to the left of the property name.

A variant property is one that has a modified value even though it is inherited from the property class associated with the object. You can override the setting of any inherited property to make that property variant. Variant properties are displayed with a red cross over an arrow.

With subclassing you can make an exact copy, and then alter the properties of some objects if desired. If you change the parent class, the changes also apply to the properties of the subclassed object that you have not altered. However, any properties that you override remain overridden. This provides a powerful object inheritance model.

When you subclass a data block, you can:

You can copy or subclass objects:

When you drag objects, a dialog box appears that asks whether you want to copy or subclass the object.

When you copy an object, a separate, unique version of that object is created in the target module. Any objects owned by the copied object also get copied. Changes made to a copied object in the source module do not affect the copied object in the target module.

With subclassing, you can make an exact copy, and then alter the properties of some objects. If you change the parent class, the changes also apply to the properties of the subclassed object that you have not altered.

When you subclass a data block you cannot:

An object group is a logical container for a set of Forms Builder objects.

You need to define an object group when you want to package related objects for copying or subclassing in another module or if you want to bundle numerous objects into higher-level building blocks that you can use again in another application. You can package the various objects in an object group and copy the entire bundle in one operation.

Object libraries are convenient containers of objects for reuse. They simplify reuse in complex environments, and they support corporate, project, and personal standards. An object library can contain simple objects, property classes, object groups, and program units, but they are protected against change in the library. Objects can be used as standards (classes) for other objects.

Object libraries appear in the Navigator if they are open. You can create, open, and close object libraries like other modules. Forms Builder automatically opens all object libraries that were open when you last closed Forms Builder.

Note: You cannot modify objects inside the object library itself. To make changes, drag the object into a form, change it, and drag it back to the object library.

A SmartClass is a special member of an Object Library. It can be used to easily subclass existing objects in a form using the SmartClass option from the right mouse button popup menu.

To use Object Library members which are not SmartClasses, you have to use the Subclass Information dialog available in the Property Palette of the form object that you are modifying.

If you frequently use certain objects as standards, such as standard buttons, date items, and alerts, you can mark them as SmartClasses by selecting each object in the object library and choosing Edit > SmartClass. You can mark many different objects, spread across multiple object libraries, as SmartClasses.

To apply a SmartClass to a Forms object, perform the following steps:

1. Right-click an object in the Layout Editor or Navigator.

2. From the pop-up menu, select SmartClasses. The SmartClasses pop-up menu lists all the SmartClasses from all open object libraries that have the same type as the object, and, for items, also have the same item type; for example, push button, text item.

3. Select a class for the object; it then becomes the parent class of the object. You can see its details in the Subclass Information dialog box in the object’s Property Palette, just like any other subclassed object.