I would add the following item to events that can invalidate a pointer to
field text:
d. If the user edits the text in the field, the pointer can become invalid
if the memory manager has to unlock the chunk holding the text, resize, and
possibly move the chunk, and then lock the chunk again.
At least that's what's in my copy of "Palm Programming: The Developer's
Guide".
Mitch
> -----Original Message-----
> From: Ken Krugler [SMTP:[EMAIL PROTECTED]]
> Sent: Monday, March 22, 1999 1:27 AM
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Re: field pointer persistence
>
> Owen said:
>
> >How long is a pointer returned by FldGetTextPtr guaranteed to be valid?
> >
> >Obviously, changing the field text could invalidate it, but what other
> >actions render the pointer "unsafe"?
>
> and Ingo replied:
>
> >If I understood things right, as long as you lock the handle associated
> with
> >the memory the pointer points to. Unlocked data can be relocated any
> time.
> >
> >In an application I am writing, I use FldSetTextPtr/FldGetTextPtr with
> >pointers to text which is declared as const in the C source code.
> Hopefully,
> >the application won't be relocated while running.
> >
> >Does anyone know whether this is true?
>
> 1. If you've got a typical editable field, then the pointer returned by
> FldGetTextPtr should be valid until:
>
> a. You make another call to the field code. Some of the Field APIs
> would seem safe to call, but given the dynamic nature of the rom code,
> you're better off not relying on the pointer staying valid.
>
> b. You make a call to something that in turn calls a field routine.
> For example, the form code will call the field code to dispose of the
> handle when the form is being tossed.
>
> c. The field's text handle gets munged by you or some other routine
> which knows about it. Obviously if you mess with the handle then all bets
> are off.
>
> Note that if the field is empty, then the call to FldGetTextPtr can return
> null if the text handle never had to be allocated.
>
> 2. If you've got a field is not editable, then the ptr won't change on
> you..and you don't have to worry about the application getting relocated
> while running.
>
> -- Ken
>
> Ken Krugler
> TransPac Software, Inc.
> <http://www.transpac.com>
> +1 650-947-9222 (direct) +1 408-261-7550 (main)
>
>
