MemHandleLock "locks down" a moveable chunk of memory. For every lock, you
should unlock it to allow the memory manager to handle the moveable chunk of
memory. (MemHandleUnlock)
Using MemHandleFree, allows this piece of memory to be written over. For
example, in a common function used by many people...
FieldPtr SetFieldTextFromHandle(Word fldID, Handle txtH)
{
Handle oldTxtH;
FormPtr frm;
FieldPtr fld;
// Get the Active Form
frm = FrmGetActiveForm();
// Get the Pointer to the Field
fld = FrmGetObjectPtr(frm, FrmGetObjectIndex(frm, fldID));
// Error?!
ErrNonFatalDisplayIf(!fld, "Incorrect Field Specified");
// Swap handles!
oldTxtH = FldGetTextHandle(fld);
FldSetTextHandle(fld, txtH);
// Clear field display
FldEraseField(fld);
// Draw field display
FldDrawField(fld);
// Free some memory baby!
if(oldTxtH)
MemHandleFree(oldTxtH);
// Return the field
return(fld);
}
Note that to replace the string present in the field, we grab the existing
handle and set a new handle to the field. Then the old handle is freed
forever.
I would highly recommend that you don't use any handle after it's been
freed. Just because the data seems to be there when you access afterwards,
it doesn't mean it won't be written over, and lead to bugs in the future.
Regards,
--
Tim Astle
--
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