addlistener question...

I have created a listener which calls 'myfunction' whenever the limits of a certain set of axes changes:

       addlistener(handles.axes1,'XLim', 'PostSet', @myfunction);

       function myfunction
       ...

This works fine. Now I want to pass the handles structure to myfunction:

      addlistener(handles.axes1,'XLim', 'PostSet',{@myfunction,handles});

      function myfunction(handles)
      ...

However I recieve the error:

      callbacks need to be of type function handle

I cannot pass handles, or any additional arguments to myfunction in this case. Why is this so? How would I set up a listener object properly?

Answer 1

[Jan]

The posted example does not work on my computer under Matlab 2011b:

addlistener(handles.axes1,'XLim', 'PostSet', @myfunction);

function myfunction   % ERROR

Calling the callback function fails, because it needs at least 2 inputs:

function myfunction(ObjH, EventData)  % OK

If you need a third input:

addlistener(handles.axes1,'XLim', 'PostSet', ...
   @(ObjH, EventData) myfunction(ObjH, EventData, handles));

function myfunction(ObjH, EventData, handles)

[Frank]

Awesome thanks.

Answer 2

[Walter Roberson]

addlistener(handles.axes1,'XLim', 'PostSet', @(varargin) myfunction(varargin{:}, handles.axes1);

Then

function myfunction(varargin)
  handles = guidata(varargin{end});
  ...
end

Answer 3

[aodhan]

First I wanted to say thanks jan, I was struggling to pass the handles object into my callback function.

I wanted to add an additional example that someone might find useful. It uses the trick above to update a text box "while" a slider is being moved, rather than just updating the value after the mouse has been released.

% first add a listener to your program. I added mine to the function that executes just before the UI is made visible.

          addlistener(handles.sDamping_slider,'Value', 'PostSet', ...
          @(ObjH, EventData) myfunction(ObjH, EventData, handles));

% Now define the actual function that gets called "myfunction"

    val = get(handles.sDamping_slider,'Value');

    set(handles.sDamping_edit, 'String', num2str(val))