Directives
PROPERTY Declare Object Properties
   
Format
1. Declare Property: PROPERTY [ HIDE ] prop1 [ OBJECT ], prop2 [OBJECT], ...
2. Specify Read Procedure: PROPERTY [ HIDE ] prop1 [ OBJECT ] GET label | ERR, prop2 ...
3. Specify Write Procedure: PROPERTY [ HIDE ] prop1 [ OBJECT ] SET label | ERR, prop2 ...

Where:

ERR Keyword blocking reads or writes to a property following a GET/SET declaration.
GET Keyword indicating that logic is to be called when properties are read.
HIDE Keyword indicating that method is not to be displayed in the list of methods returned by '*
label Statement label indicating GET or SET logic entry point.
OBJECT Optional keyword identifies that the property contains an object identifier to another object.
prop1, Property names – treated like any other variable in the system. (In
prop2 .. Object Oriented Programming, data is referred to as properties.)
SET Keyword indicating that logic is to be called when properties are written.

The HIDE option is a +PxPlus Exclusive (build 9182)  

   
Description The PROPERTY directive is used in Object Oriented Programming to declare the properties that can be accessed by the application program. These properties can be treated like any other variable in the system and are accessible using the Apostrophe Operator.

A property name can be followed by a GET label to define the location of the logic to call whenever the property is read in the application. With GET in place, the specified logic issues a RETURN value that returns the actual value of the property to the application. For example:

    PROPERTY ExtendedAmount GET Extension
      ...
Extension:
    RETURN Quantity * Price

If the logic resides outside of the defining program, then the name of the program and entry point can be provided in quotes instead.

*Note* If the logic required to do a read is simply a formula, then it can be inserted directly into the PROPERTY definition clause using an equals sign instead of using a subroutine and a GET declaration. For Example:

PROPERTY ExtendedAmount = Quantity*Price
   Specify the SET label to intercept all of the property updates. With SET in place, the system calls the logic whenever the property is being updated and passes it the value being set.

For Example:

PROPERTY Quantity SET ChgQty

Like the GET option, an external program/entry point can be provided as in:

PROPERTY Quantity SET "Invline;ChgQty"

Where Invline contains:

2000 ChgQty:
2010 ENTER NewQty
2020 IF NewQty = Quantity then RETURN
2030 ! .. Update inventory.. then RETURN

Use the keyword ERR to prevent the user from being able to GET or SET a property following the GET or SET declaration.

PROPERTY ExtendedAmount SET ERR

If the property contains an object identifier to another object, specify the keyword OBJECT after the property name. When the object is deleted, ProvideX will use the REF( ) function against the object identifier to remove it (as long as it has no other references) as in:

DEF CLASS "Customer" PROPERTY File OBJECT

When you delete an object whose class is Customer, then the system reduces the reference count of the object whose identifier is in File and, if it is no longer being referenced, deletes it as well.

For defining properties for an object class that are not exposed to external applications, refer to the LOCAL Directive.

   
See Also Object Oriented Programming
DEF CLASS Define Object Class
DROP CLASS Delete Class Definition
DROP OBJECT Delete Object
FUNCTION Declare Object Method
LIKE Inherit Properties
LOAD CLASS Pre-Load Class Definition
LOCAL Designation of Local Data
PROGRAM Create/Assign Program File
RENAME CLASS Change Name of Class
STATIC Add Local Properties at Runtime
NEW( ) Function
REF( ) Function