* Josh Babcock -- Monday 30 January 2006 22:01:
* > > On Sunday 29 January 2006 16:20, Melchior Franz wrote:
> > > set the /sim/signals/reinit property on reinit, so that aircraft code can
> > > attach listeners.
> I think I missed something earlier. Can someone describe the
> functionality that has been added?
There's a Nasal interface to the property listener feature since
a few weeks. If one attaches a listener to a property, it will be
executed whenever the property is written to (no matter which
value -- it's not about *changing* values). These listeners are
implemented directly in the property node, and *every* write
access will trigger them, even when setting via telnet/http
or from c++. The listeners should be used instead of polling
loops, if the property isn't tied and isn't written to frequently.
The triggering property node is available as cmdarg().
Examples:
setlistener("/sim/crashed", func { print("we crashed!") });
replayNode = props.globals.getNode("/sim/freeze/replay-state");
replay = func { print("replay " ~ ["off", "on"][cmdarg().getBoolValue()]) }
setlistener(replayNode, replay);
Because setlistener() uses cmdarg(), which uses props.Node, one can
only use it after the props.nas module has been loaded. Files in
$FG_ROOT/Nasal/ should therefore use setlistener in an INIT style
timer function. setlistener() takes an optional third bool argument,
that tells if the callback function should be executed initially:
Example:
setlistener("/environment/metar/real-metar",
func { print(cmdarg().getValue()) }, 1);
This prints the current metar string and every new one.
Yesterday I added two properties solely for the purpose of attaching
Nasal listeners. They can be used for callback functions:
/sim/signals/reinit -- set on reinit (Shift-Esc)
/sim/signals/exit -- set on exit
Examples:
setlistener("/sim/signals/reinit", reset_function);
atexit = func(f) { setlistener("/sim/signals/exit", f) }
atexit(save_my_stuff);
m.
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