Delete a handles parameter

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Jason
Jason on 23 Sep 2014
Commented: Chandan Prakash on 1 Jul 2020
I have a set of subplots that I plot on the canvas. I collectively assign to the handles structure using
handles.CanvasPlot=hSubplots; %assign hSubplots to a handle called CanvasPlot
guidata(hObject, handles); % Update handle structure
and then delete when its required as:
if isfield(handles,'CanvasPlot')
delete(handles.CanvasPlot);
end
But it appears to delete this when its not present, i.e. when I first load code, there is no hsubplots and hence CanvasPlot, I thought the check above would catch this. I get the error
Error using delete
Invalid or deleted object.
Error in Montage>pushbutton1_Callback (line 124)
delete(handles.CanvasPlot);
Im not sure whats happening. Thanks Jason
  1 Comment
Adam
Adam on 23 Sep 2014
Edited: Adam on 23 Sep 2014
Just to add a comment to tie together the two answers below which both explain their part of the functionality well. You may know all this anyway, but in case someone else looks at your question later on hoping to solve a similar problem:
There are two different aspects going on here and I assume you want both parts.
  • Calling 'delete' as you are (and as Sean de Wolski is explaining syntax for below) is done on a graphics handle(s) (or a handle-derived object in OOP) and will delete the graphics object. However it will leave the field still there on handles pointing to a deleted graphics object
  • Using rmfield as Image Analyst shows below is the second part of that which will remove the field from handles that now points to a deleted graphics object.
Personally in the latter case I tend to just set the field to [] and test using isempty at other points in my code (having created the field in the GUI's OpeningFcn) rather than removing the field ans testing with isfield, but both methods are equally valid.
One advantage to using the [] option though is that you can call the equivalent of
delete( [] )
without a syntax error. However, what you can't do is call
delete( someGUIHandle )
if 'someGUIHandle' is neither empty nor a valid handle (i.e. you have deleted it as you do above) so you do usually still need to do the ishandle( someGUIHandle ) checks before calling delete to be sure.

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Accepted Answer

Image Analyst
Image Analyst on 23 Sep 2014
I don't think you can do that. You need to use rmfield() instead.
handles = rmfield(handles, 'CanvasPlot');
  2 Comments
Jason
Jason on 23 Sep 2014
Thankyou, this works:
if isfield(handles,'CanvasPlot')
handles = rmfield(handles, 'CanvasPlot');
end
Chandan Prakash
Chandan Prakash on 1 Jul 2020
Thank you. This works perfect.

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More Answers (1)

Sean de Wolski
Sean de Wolski on 23 Sep 2014
dbstop if error
Will stop in debug mode when the error is thrown. You can see what it's doing here. Another thing you could do is check that they are handles:
if isfield(handles,'CanvasPlot') && ishandle(handles.CanvasPlot)
delete(handles.CanvasPlot);
end
  10 Comments
Jason
Jason on 25 Sep 2014
looks like this works:
delete(get(handles.uipanelM,'Children'))
Jason
Jason on 25 Sep 2014
Yes IA, all the images did array (or montage), just all a bit smaller, so I can play with that part. the delete worked too using this way:
delete(get(handles.uipanelM,'Children'))

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