why guidata not saving handles data

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Hi,
I've inserted these 2 lines in my GUI opening function:
handles. hText = '';
handles.allLines = [];
set(gcf, ...
'WindowButtonDownFcn', {@clickFcn, handles}, ...
'WindowButtonUpFcn', @unclickFcn);
I've a code that I added 2 data 'allLines' and 'hText'
function plot2_push_Callback(hObject, eventdata, handles)
handles.allLines = findobj(gcf, 'type', 'line');
handles.hText = nan(1, length(handles.allLines));
for id = 1:length(handles.allLines)
handles.hText(id) = text(NaN, NaN, '', ...
'Parent', get(handles.allLines(id), 'Parent'), ...
'BackgroundColor', 'yellow', ...
'Color', get(handles.allLines(id), 'Color'));
end
guidata(hObject, handles);
then I would like to use it here:
function clickFcn(hObject, eventdata, handles)
a = 1;
b = handles.hText;
c = handles.allLines;
disp(a)
disp(b)
disp(c)
but looks like the handles structure does not save the data from the plot callback..
how can I solve this? Thanks.
  2 Comments
James Ang
James Ang on 28 Mar 2016
I realized it'll only update if I set the opening lines into the plot function as below:
function plot2_push_Callback(hObject, eventdata, handles)
handles.allLines = findobj(gcf, 'type', 'line');
handles.hText = nan(1, length(handles.allLines));
for id = 1:length(handles.allLines)
handles.hText(id) = text(NaN, NaN, '', ...
'Parent', get(handles.allLines(id), 'Parent'), ...
'BackgroundColor', 'yellow', ...
'Color', get(handles.allLines(id), 'Color'));
end
guidata(hObject, handles);
set(gcf, ...
'WindowButtonDownFcn', {@clickFcn, handles}, ...
'WindowButtonUpFcn', @unclickFcn);
but why?

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Accepted Answer

Walter Roberson
Walter Roberson on 28 Mar 2016
When you coded
handles. hText = '';
handles.allLines = [];
set(gcf, ...
'WindowButtonDownFcn', {@clickFcn, handles}, ...
'WindowButtonUpFcn', @unclickFcn);
then a copy of the value of the "handles" structure is recorded for use with WindowButtonDownFcn . But that copy has the empty values for those fields, so when you invoke the callback, the fields will be empty in the callback.
You have two choices:
  1. Make "handles" a shared variable (and do not pass it around), so that all changes to "handles" are changing the same variable; or
  2. Pass something into the callback that you can use to locate the master handles structure at the time of the callback
If you are using multiple figures and the handles structure is not attached to the same figure as the WindowButtonDownFcn is acting on, then you need to pass in the figure number that WindowButtonDownFcn is acting on (or you need to pass in some object that exists in that figure.)
If you are using only a single figure, or the handles structure is attached to the same figure that the WindowButtonDownFcn is acting on, then you already have something that can be used to locate handles: namely hObject can be used to locate the master handles structure in such a case:
handles = guidata(hObject);
with no need to pass handles in.

More Answers (1)

Antoine Hurtado Huyssen
Antoine Hurtado Huyssen on 29 Aug 2017
each time you add Something to your handles you need to update the guidata
guidata(hObject,handles);
  1 Comment
Walter Roberson
Walter Roberson on 29 Aug 2017
That is not sufficient in this situation. The user had coded
'WindowButtonDownFcn', {@clickFcn, handles}, ...
which causes a copy of the handles structure to be taken and that copy would be what would be passed to clickFcn. Using guidata() to update the master version of the handles structure would not update the copy that was saved.

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