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  • #21
    MCM ... something I ran across about DDT's CALLBACK function use, from http://www.powerbasic.com/support/fo...ML/006703.html
    I'd guess that might be about as "official" as it ever got, but then probably there are more such exchanges in the archives. [Note: Lance left PowerBASIC some time past, this reference is from when he was working for them.]

    'Lance Edmonds, Member
    'posted September 23, 2002 12:52 AM

    Edwin, you can certainly use a DDT Callback for a subclass procedure... no problemo, unless the automatic %DWL_MSGRESULT update is a problem - which it invariably never is.

    ....
    (in an exchange on subclassing with Edwin Knoppert
    ... then next post by Lance in this thread says:

    heh. You do seem hung up on using an SDK-style wndproc for some reason, Edwin.

    If we look at the situation with using a DDT Callback Function, is is a simple matter to use a local variable in place of CBWPARAM in the CallWindowProc() statement, so we can
    completely control that parameter before it is passed to the original TEXTBOX window procedure.

    Additionally, the %WM_CHAR message can be discarded completely by an EXIT FUNCTION in the WM_CHAR handler, which effectively kills the message outright. This is a standard
    subclass technique, no less.


    ------------------
    Lance
    PowerBASIC Support
    Last edited by Richard Angell; 16 Oct 2007, 10:08 AM. Reason: clarification
    Rick Angell

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