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  • #21
    MCM ... something I ran across about DDT's CALLBACK function use, from
    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.

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