Delete a handles parameter

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

[Adam]

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.

Answer 1

[Image Analyst]

I don't think you can do that. You need to use rmfield() instead.

handles = rmfield(handles, 'CanvasPlot');

[Jason]

Thankyou, this works:

if isfield(handles,'CanvasPlot')
     handles = rmfield(handles, 'CanvasPlot'); 
    end

[Chandan Prakash]

Thank you. This works perfect.

Answer 2

[Sean de Wolski]

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

[Jason]

Thanks Sean, I tried but got this error:

Operands to the || and && operators must be convertible to logical scalar values.

Error in Montage>pushbutton1_Callback (line 124)
    if (isfield(handles,'CanvasPlot')&& ishandle(handles.CanvasPlot))

[Sean de Wolski]

Probably:

all(ishandle(handles.CanvasPlot))

Since there are multiple. But depending on what you want to do this might not be right anyway. My code deletes the subplot axes; IA's removes the field from the structure - two different operations.

[Image Analyst]

It would delete the axes if you had assigned handles.CanvasPlot to some variable and deleted that variable instead of handles.CanvasPlot. Look at the following simple code - it fails when you try to delete one of the fields.

h.a = 1;
h.b = 2
delete(h.a) % Fails

[Sean de Wolski]

But not if figure 1 is open:

h.a = 1;
figure(1)
pause(1)
h.b = 2
delete(h.a) % woohoo

[Jason]

Is it possible to draw draw my subplots onto a uipanel, and then just clear this?

[Adam]

You could quite easily get all children of the panel, check if they are axes and if they are call 'cla' on them.

As discussed above though, this will, of course, still leave you with deleted handle references if you stored the handles of the plots in your handles.CanvasPlot field.

[Jason]

So Ive tried this:

Draw the plots to the uipanel,

hp = handles.uipanelM

     h=subplot('Position',positionVector,'Parent',hp);

Then to clear (as wanting to draw again later)

cla(handles.uipanelM,'reset');

[Image Analyst]

Did that work? Did all the plots show up arrayed inside the panel rather than on the main figure?

[Jason]

looks like this works:

delete(get(handles.uipanelM,'Children'))

[Jason]

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'))