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VFP COM Design Problem
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General information
Forum:
Visual FoxPro
Category:
COM/DCOM and OLE Automation
Miscellaneous
Thread ID:
01214563
Message ID:
01214594
Views:
10
>I should have mentioned that I want it to be OLEPUBLIC, as I want it to appear
>in the object browser.
>
>It is necessary for users to be able to view the properties and methods on the
>child class. I just want to prevent them from instantiating it from outside
>the main class.
>
>
>
>>Kevin REmove the OLEPUBLIC keyword from your DEFINE CLASS stament for the class you don't want to be instantiated from the outside world, only classes mark as OLEPUBLIC are allowed to be created by an outside application.
>>
>>>I have PRG-based classlib that will be compiled into a DLL. There are classes in
>>>the DLL that I only want instantiated through methods in the main class.
>>>
>>>The problem is how to prevent a class from being instantiaed from outside the
>>>main class.
>>>
>>>One solution that I came up with is this:
>>>
>>>
>>>
>>>** Main Class
>>>PROCEDURE GetChildClass() AS Object
>>>
>>>  LOCAL oRetVal AS Object
>>>
>>>  PUBLIC gb_AllowChildClass && This must exist in the child class Init
>>>
>>>  oRetVal = This.GetChildClass()
>>>
>>>ENDPROC
>>>
>>>
>>>And in the Child class's Init:
>>>
>>>PROCEDURE Init()
>>>
>>>  LOCAL bRetVal AS Boolean
>>>  bRetVal = .T.
>>>
>>>  IF TYPE("AllowChildClass") = "U"
>>>    bRetVal = .F.
>>>  ENDIF
>>>
>>>  RETURN bRetVal
>>>
>>>ENDPROC
>>>
>>>
>>>Since the whole thing is in a DLL, it's in its own session, so there should
>>>be no issue with using a public variable.
>>>
>>>Still, I don't really feel good about it.
>>>
>>>Anyone have a better way?


How about:
** Main Class
PROCEDURE GetChildClass() AS Object

 LOCAL oRetVal AS Object

 PUBLIC gb_AllowChildClass && This must exist in the child class Init

 oRetVal = This.GetChildClass([SomeUniqueStringYouImagnie])

ENDPROC


*And in the Child class's Init:


PROCEDURE Init(lcUniqueString)

  LOCAL bRetVal AS Boolean
  bRetVal = .T.

  IF NOT lcUniqueString == SomeUniqueStringYouImagnie
     bRetVal = .F.
  ENDIF

  RETURN bRetVal

ENDPROC
Then from your main class you could do:
oRetVal = This.GetChildClass([AbraKadabra])
and in Init of the Child Class:
PROCEDURE Init(lcUniqueString)

  LOCAL bRetVal AS Boolean
  bRetVal = .T.

  IF NOT lcUniqueString == [AbraKadabra]
     bRetVal = .F.
  ENDIF

  RETURN bRetVal

ENDPROC
Against Stupidity the Gods themselves Contend in Vain - Johann Christoph Friedrich von Schiller
The only thing normal about database guys is their tables.
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