Q131133: How to Create and Access Protected Properties

Article: Q131133
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): kbcode
Last Modified: 15-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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SUMMARY
=======

In Visual FoxPro, programmers can make user-defined object properties visible
only to the events and methods for the defined object by protecting them from
access by outside objects. Protected properties can only be altered or
referenced by using the object's methods and events.

By using the PROTECTED keyword for properties in a class definition, protected
properties cannot be changed by other objects. For example, when designing a
form class that has a command button, the command button is unable to modify the
PROTECTED Methods or Properties of the form class.

This article shows by example how to create a new custom class with some
protected properties and a custom method ProtProperty. The protected properties
cannot be accessed by external commands unless they use the custom method
(ProtProperty) of the object.

MORE INFORMATION
================

The Help menu says, "Properties, methods, and objects in a class definition that
are designated protected with the PROTECTED keyword of the DEFINE CLASS command
can be accessed only by other methods in the class definition."

Code Sample
-----------

  *--------------------------------------------------------------*
  * PROGRAM: PROTTEST.PRG                                        *
  *                                                              *
  * Copy this code into a PRG and then execute the PRG.          *
  *--------------------------------------------------------------*
  oMyObject = CREATEOBJECT("MyClass")

  ? oMyObject.One

  * The command shown above fails because property ONE is not   *
  * being accessed through a method of the custom class. When   *
  * this fails, choose IGNORE and the program will continue.    *

  ? oMyObject.ProtProperty("ONE")
  ? oMyObject.ProtProperty("TWO")
  ? oMyObject.ProtProperty("THREE")

  DEFINE CLASS MyClass AS Custom
    PROTECTED One, Two, Three
    One   = "ONE"
    Two   = 2
    Three = "THREE"

    FUNCTION ProtProperty(lcProperty)
      RETURN EVAL("THIS."+lcProperty)
    ENDFUNC
  ENDDEFINE
  *--------------------------------------------------------------*

Additional query words: VFoxWin Encapsulation read_only

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Keywords          : kbcode 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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