How to pass variables into a callback function in matlab (with addlistener)

Question

I'm working on a continuously updating slider...

hsl = uicontrol(...); % Slider initializing stuff
vars=struct('hsl', hsl, 'x', x, 'y', y); % A bunch of stuff that my callback needs
set(hsl,'Callback',{@hsl_callback,vars});

addlistener(hsl,'ContinuousValueChange',@hsl_callback);

Here's the problem. If I leave it like that, I get the error "not enough input arguments" for the callback.

If I change the line to this:

addlistener(hsl,'ContinuousValueChange',@(vars)hsl_callback);

then I get the error "too many input arguments."

Is this not possible, or am I getting the syntax wrong?

If it helps, my callback function has this structure:

function hsl_callback(~,~,vars)
    k = get(vars.hsl,'Value');
    % plot x, y scaled by k
end

try addlistener(hsl,'ContinuousValueChange',@() hsl_callback(vars));? — user3528438
– user3528438, Commented Aug 10, 2015 at 21:25
I just did, but it still says that there are too many input arguments. — arrey
– arrey, Commented Aug 10, 2015 at 22:39
I have also tried addlistener(hsl,'ContinuousValueChange',@{hsl_callback,vars});, which doesn't work either. — arrey
– arrey, Commented Aug 10, 2015 at 23:43

Juderb · Accepted Answer · 2015-08-11 07:29:08Z

2

First, I would avoid using vars to store your data. The slider handle can be passed directly in your callback, and x and y may be stored in the UserData property. This gives you the ability to change x and y dynamically, if needed. Change your callback method declaration to:

function hsl_callback(hObject,eventdata)
  % Retrieve k and vars
  k = get ( hObject , 'Value' );
  vars = get ( hObject , 'UserData' );

  % Plot x,y scaled by k
  ...
end

Then, I would change slider creation to:

% Define x and y.
vars = struct('x',x,'y',y);

% Create slider, assigning vars to UserData.
hSlider = uicontrol('Sytle','Slider',...,'UserData',vars);

% Assign the callback method, executed whenever the slider is released.
set(hSlider,'Callback',@hsl_callback);

% Assign the listener, executing whenever the slider value changes.
hListener = addlistener(hSlider,'ContinuousValueChange',@(src,eventdata)hsl_callback);

Depending on your version, you may have to use this instead:

hListener = addlistener ( hSlider , 'Value' , 'PostSet' , @(src,eventdata)hsl_callback );

edited Aug 11, 2015 at 7:29

answered Aug 11, 2015 at 7:08

Juderb

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2 Comments

arrey Over a year ago

Thanks for the suggestion, this seems like a better way to handle passing in data. However, I'm still getting the same error on the addlistener line- not enough input arguments.

arrey Over a year ago

Oops, this is the working code: hListener = addlistener(hSlider,'ContinuousValueChange',@hsl_callback);

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