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Introduction to Class Programming

Property Get/Let

Every time you assign a new value to a property, Visual Basic checks whether there's an associated Property Let procedure and passes the new value to its associated Private variable. If the code can't validate this new value, it raises an error and throws the execution back to the caller. Otherwise, the execution proceeds by assigning the value to the Private variable.  And when the caller code requests the value of the property, Visual Basic executes the corresponding Property Get procedure, which simply returns the value of the Private variable. Try to trace your code by pressing F8,  and see what actually those property procedure do. 

NOTE
The type expected by the Property Let procedure must match the type of the value returned by the Property Get procedure.

You might be asking this question, "Why not just use a public variable to store property values?  In a sense, we are just using a sort of indirection. Why not use function to return a value or sub to assign a value" In some cases that may work fine; however, if you want to make sure that the value assigned to the property is valid, you have to write validation code when the value is assigned. And usually you this by creating a Sub or Function to validate the public variable or worst you end up coding a lot in the client (form) for this validation routine.  It end up, we did not benefit for the characteristic of OOP which is encapsulation, stated that "an object is the sole owner of its own data." And this is the benefit of using a property procedure.

Comments

  1. 26 Jun 2009 at 13:14

    Wouw, thanks for this great explanation on how to use and make classes. I always coded in VB with function in normal Modules, now i'm going one step further... Trying it out...

  2. 23 Jun 2009 at 10:37

    Great Tutorial !! Helped me a lot

  3. 07 Mar 2009 at 10:54
    This is great tutorial! Thank you sooooo much.
  4. 07 Jun 2008 at 11:55

    [quote user="Developer Fusion Bot"]

    This thread is for discussions of Introduction to Class Programming.

    [/quote]

    This was the best explanation to "class", I have ever come across. Hats off to you.

  5. 12 Jul 2007 at 12:36

    Hello Sir,

    I have just seen u'r examples for class module.u'r explaination is simply superb!!!!

    now i clearly understood the class module concept in VB.

     

    Thanks

    Bhavani Josyula

  6. 15 May 2007 at 16:10
    This was a very good fundamental article on the use of classes in VB. looking forward to additional more advance content
  7. 16 May 2006 at 11:35

    It s a great sample about the class programming. However, it s still uncertain for me where I can use this in real life.

    Can anyone give me an example ?

  8. 05 Oct 2005 at 19:12

    what kind of help you wants from me. i mean to clear out your visual basic basics by giving you some tutorials or anything else. bye

  9. 29 Sep 2005 at 12:25
    hello sir, can you teach me the visual basic programing and where to start because i don't have a basic in this software. before this, i was try to learn this programe from e_book but it's looking so hurt to learn without a teacher.
    I would appericiate if u can show me the way to learn this programe.
    TQ
  10. 16 Jul 2005 at 02:59
    Thanks, Dante Salvador, for your excellent and lucid tutorial on Class Programming.
    I have worn Google to a frazzle looking for help. most of which was comprised of a few samples.
    You have helped "elucidate" me with both the why and how-to and that is no small task.
    Thanks so much for your efforts and help.
  11. 09 Jun 2005 at 17:34

    What a tutorial !! man i like it. this tutorial shows me another side of visual basic wow!!

  12. 23 Dec 2004 at 13:40

    This is really a good tutorial on Visual Basic. I was really coinfused between let, get properties. But this is the final place which solved ll my problems

  13. 22 Oct 2003 at 11:52

    vbexplorer.com has also an excellent oop tutorial, if youre looking for some more,
    and I have found a german article at vbarchiv.de that seems very good (i can
    tell because I studied german when in grad. school, swe).


    Maybe I should try an translate it to english...

  14. 20 Sep 2003 at 06:32

  15. 10 Sep 2003 at 17:41
    At one time I studied programming in Pascal & Fortran --- have forgotten lots of basics....I have read thru many VB tutorials etc but never have I so clearly had the 'light bulb' go on.  Thank-you for a well organized presentation.  Look forward to your future articles.
  16. 01 Jan 1999 at 00:00

    This thread is for discussions of Introduction to Class Programming.

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