Re: Multiple addlistener calls?

[Ben Abbott]

> On Jul 29, 2015, at 2:25 PM, Rik <address@hidden> wrote:
> 
> All,
> 
> Should it be possible to add the same function multiple times as a listener 
> on a graphics property?
> 
> -- Start Code --
> octave:1> function mycb (~,~)
> > disp ("Executing mycb");
> 
>       > endfunction
> octave:2> h = plot (1:10);
> 
> octave:4> addlistener (h, 'color', @mycb)
> octave:5> set (h, 'color', 'r')
> Executing mycb
> octave:6> addlistener (h, 'color', @mycb)
> octave:7> set (h, 'color', 'g')
> Executing mycb
> Executing mycb
> octave:8> addlistener (h, 'color', @mycb)
> octave:9> set (h, 'color', 'b')
> Executing mycb
> Executing mycb
> Executing mycb
> octave:10> dellistener (h, 'color', @mycb)
> octave:11> set (h, 'color', 'm')
> Executing mycb
> Executing mycb
> Executing mycb
> -- End Code --
> 
> It's making things awkward in legend.m where I'm trying to avoid multiple 
> listener assignments.  If the C++ code were to weed these out it would make 
> the m-file simpler.  Otherwise, I have to figure out which new legend objects 
> were part of an existing legend and avoid adding listeners on just those 
> instances.

I don’t recall intending to have the same function registered as a listener on 
a property more than once. I do recall worrying about that.

If a change is made, I expect there will be some problems, but I also expect 
they will be more manageable than the current implementation.

While you’re modifying this part of the code, would it be possible to add a 
getlistener(h,prop) function, and have it return a cell array of the register 
listeners? I expect this idea is superficially simple but quite complex to 
implement, but just in case it is straight forward, I thought I’d ask.

Ben