> // how to call oldTrap with vars?
> PrgUpdateDialog(prgP, err, stage, messageP, updateNow);
> ...
> oldTrap = *(UInt32*)SysGetTrapAddress(sysTrapPrgUpdateDialog);
First, you need access to oldTrap. Save it in a feature. Then you can access
it when myPrgUpdateDialog() gets called. To call the old function, cast it
to a pointer to a function with the appropriate parameter types (if it isn't
already that type), dereference it, and then call it as usual.
First, get the old trap address, save it in a feature, and then patch the
trap:
void (*oldTrap)(ProgressPtr prgP, UInt16 err, UInt16 stage,
Char *messageP, Boolean updateNow);
oldTrap = SysGetTrapAddress(sysTrapPrgUpdateDialog);
err = FtrSet('Crid', 0, (UInt32)oldTrap);
err = SysSetTrapAddress(sysTrapPrgHandleEvent, &myPrgUpdateDialog);
// the & is optional - it has no effect
Then, when your patched function runs, it grabs the address of the old
function out of the feature and calls it with the modified parameter:
void (*oldTrap)(ProgressPtr prgP, UInt16 err, UInt16 stage,
Char *messageP, Boolean updateNow);
err = FtrGet('Crid', 0, (UInt32 *)&oldTrap);
(*oldTrap)(prgP, 0 /* err */, stage, messageP, updateNow);
// call the original function, but force the error code off
// if there was a result, we'd return it, but this function returns void
When you're all done, unpatch the trap:
void (*oldTrap)(ProgressPtr prgP, UInt16 err, UInt16 stage,
Char *messageP, Boolean updateNow);
err = FtrGet('Crid', 0, (UInt32 *)&oldTrap);
err = SysSetTrapAddress(sysTrapPrgHandleEvent, oldTrap);
Of course you'll want to use your app's creator ID, use a named constant for
the feature number, and handle error returns. :)
Actually, you could probably use a global variable rather than a feature
since you're unpatching the trap before your app quits. This simplified
things considerably:
static void (*OldTrap)(ProgressPtr prgP, UInt16 err, UInt16 stage,
Char *messageP, Boolean updateNow);
...
OldTrap = SysGetTrapAddress(sysTrapPrgUpdateDialog);
err = SysSetTrapAddress(sysTrapPrgHandleEvent, &myPrgUpdateDialog);
...
(*OldTrap)(prgP, 0 /* err */, stage, messageP, updateNow);
...
err = SysSetTrapAddress(sysTrapPrgHandleEvent, OldTrap);
Patching traps won't be supported much longer, but it's fun while it lasts.
:)
-
Danny
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