Handle.listener, how to update code?

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Kaden 2018-10-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422889-handle-listener-how-to-update-code

回答： Divyajyoti Nayak 2024-12-26

Hi, I have an old MathWorks code that I did not write and contains handle.listener in it. It appears that Matlab has phased out this function and was replaced by addlistener. In the code below, I am getting an error in the line with the handle.listener function, how can I update the code so it continues to work as before??

Thank you!!

function updateAncestorListeners(h_group,update_fcn)
%updateAncestorListeners Set up listeners to ancestors. 
%   updateAncestorListeners(H_GROUP,UPDATE_FCN) sets up listeners to all
%   ancestors of H_GROUP that have Position, XLim, or YLim properties. H_GROUP
%   is an hggroup object. UPDATE_FCN is a function handle that is called when
%   any of the ancestor properties change.
% 
%   It's important to use updateAncestorListeners when you are drawing objects
%   in a way that may depend on the current Position, XLim, or YLim properties
%   of ancestors. If these properties change, you need to redraw your
%   object. Using updateAncestorListeners makes the code drawing objects more
%   robust to user actions like zooming and resizing.
%   $Revision $  $Date: 2005/05/27 14:07:37 $
% Clear the old listeners.
setappdata(h_group, 'AncestorPositionListeners', []);
h_parent = get(h_group, 'Parent');
root = 0;
listeners = [];
property_list = {'Position', 'XLim', 'YLim'};
while h_parent ~= root
  % Some ancestor objects might not have Position properties.
  properties = get(h_parent);
  for k = 1:numel(property_list)
    property = property_list{k};
    if isfield(properties, property)
      parent_handle = handle(h_parent);
      listener = handle.listener(parent_handle, ...
                                 parent_handle.findprop(property), ...
                                 'PropertyPostSet', update_fcn);
      if isempty(listeners)
        listeners = listener;
      else
        listeners(end + 1) = listener;
      end
    end
  end
  h_parent = get(h_parent, 'Parent');
end
setappdata(h_group, 'AncestorPositionListeners', listeners);

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Kaden 2018-10-9

Thanks! Unfortunately I saw this earlier and wasn't able to get my code running with it. I believe my error is with "update_fcn" . Any ideas on how this input needs to be modified to go from a handle.listener to a addlistener accepted input? I didn't fully understand the fourth argument difference.

Thanks!

Kevin Chng 2018-10-9

Hi Kaden, do you mind provide h_group and update_fcn script/data file for me try out?

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Answer 1

Divyajyoti Nayak 2024-12-26

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https://ww2.mathworks.cn/matlabcentral/answers/422889-handle-listener-how-to-update-code#answer_1556492

在 MATLAB Online 中打开

Hi Kaden,

To update code from using ‘handle.listener’ to ‘addlistener’, the ‘eventName’ or the third argument needs to be changed. Here’s the documentation of ‘addlistener’ which describes the requirements of the input arguments:

https://www.mathworks.com/help/matlab/ref/handle.addlistener.html?s_tid=doc_ta

Hence, the new code would be something like:

listener = addlistener(parent_handle, parent_handle.findprop(property), 'PostSet', update_fcn);

It is important to note that the parent class whose property is being listened to must set the the ‘GetObservable’ and ‘SetObservable’ attribute. Only then, listening to these properties is possible.

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