Closing MATLAB GUI application programmatically without using error() - matlab

Question

I am trying to make it so the application/gui closes completely if the user clicks cancel or exit of an input dialog. The tag of my gui is called window however using close(handles.window); leads to the program looping through once and then (after the user clicks cancel or exit again) reaching the close(handles.window); line which, of course, leads to an Invalid figure handle error.
Is there any method to close the application without the need for producing an error and not closing the entire MATLAB environment (like quit and exit). The error() is my temporary fix which works but I don't want the application to seem like it has crashed.
I have tried close all but that has no effect. It's worth noting that the application does reach inside the if statement if the user clicks cancel or exit.
I have also tried setting a variable and having the close commands outside the while loop.
apa = getAvailableComPort();
apList = '';
i = 0;
for idx = 1:numel(apa)
if i == 0
apList = apa(idx);
else
apList = strcat(apList, ', ', apa(idx));
end
i = i + 1;
end
prompt = {'Enter COM PORT:'};
title = 'COM PORT';
num_lines = 1;
def = apList;
COM_PORT = inputdlg(prompt,title,num_lines,def);
% Keep asking for a COM PORT number until user gives a valid one
while sum(ismember(apa, COM_PORT)) == 0 % If the COM port comes up in the available COM ports at least once
% If user clicks cancel, close the guide
if isempty(COM_PORT) == 1
error('Closing...'); % HERE IS THE PROBLEM
end
prompt = {'Invalid COM PORT'};
title = 'Invalid COM PORT';
COM_PORT = inputdlg(prompt,title,num_lines,def);
end
The function getAvailableComPort is found at http://www.mathworks.com/matlabcentral/fileexchange/9251-get-available-com-port
This entire piece of code is at the top of the gui_OpeningFcn() function.

Answer 1

Have you tried putting a break after the close(handles.window). The break will exit the while loop so it won't hit that line again.
if isempty(COM_PORT) == 1
close(handles.window)
break
end
This way the while loop stops after closing the window. IF you need to do more cleanup besides just closing the window then set an error flag .
%Above while loop
errorFlag = False;
if isempty(COM_PORT) == 1
close(handles.window)
errorFlag = True;
break
end
%OutSide of While loop
if errorFlag
%Do some more clean-up / return / display an error or warning
end
Also FYI, you don't need to do isempty(COM_PORT) == 1 ... isempty(COM_PORT) will return true/false without the == 1

Answer 2

Your requirements aren't really clear, but can't you just protect the close operation by doing
if ishandle(handle.window)
close(handle.window)
end
This will prevent the close from being attempted if the window has already been destroyed.

Answer 3

Why don't you use a simple return and a msgbox to inform that user has clicked on Cancel?
if isempty(COM_PORT)
uiwait(msgbox('Process has been canceled by user.', 'Closing...', 'modal'));
delete(your_figure_handle_here);
return;
end

Answer 4

I tried using the return statement in conjunction with close(handles.window) but received the error:
Attempt to reference field of non-structure array.
Error in ==> gui>gui_OutputFcn at 292 varargout{1} = handles.output;
So it seems just removing that line on 292 solved the issue.