Re: Problem with AudioUnitAdd/RemovePropertyListener
Re: Problem with AudioUnitAdd/RemovePropertyListener
- Subject: Re: Problem with AudioUnitAdd/RemovePropertyListener
- From: Brett George <email@hidden>
- Date: Sat, 16 Dec 2006 10:17:12 -0800
The view would be a bad place to have these property listeners. You
should have another class which always runs regardless of which windows
are open, and that class should update the contents of the windows based
on AU property changes.
Brett.
Ian Kemmish wrote:
>
> There appears to be a problem with the way these routines are specified.
>
> ComponentResult AudioUnitAddPropertyListener(
> AudioUnit ci,
> AudioUnitPropertyID inID,
> AudioUnitPropertyListenerProc inProc,
> void * inProcRefCon
> );
>
> ComponentResult AudioUnitRemovePropertyListener(
> AudioUnit ci,
> AudioUnitPropertyID inID,
> AudioUnitPropertyListenerProc inProc
> );
>
>
> The key to the problem is that the combination of inID and inProc is
> not always sufficient to uniquely identify a particular listener.
>
> Take the simple case of a polite AU and a polite host which allow the
> user to open multiple windows viewing the same AU, and close any of
> those windows at any time. In this case, inProcRefCon will typically
> be a pointer to an instance of some NSView subclass, and of course
> inProc will be the same for each instance.
>
> The problem is that when the user closes one of the windows,
> AudioUnitRemovePropertyListener() has no way of communicating to the
> AU which window is being closed, and therefore which listener to remove.
>
> The documentation correctly describes the behaviour of the sample
> listener code:
>
> "This function will remove *ALL* of the property listeners that match
> the specified property ID and the inProc address." (my emphasis)
>
> But the trouble with this is that it will also remove the listener(s)
> for the window(s) that is(are) left open by the user. These windows
> will promptly become deaf to property value changes. I don't believe
> this is acceptable behaviour.
>
>
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - - -
> Ian Kemmish 18 Durham Close, Biggleswade, Beds
> SG18 8HZ
> email@hidden Tel: +44 1767 601361 Mob: +44 7952
> 854387
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>
>
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