Using 'while' loop to check if a file has been added to path

Version: 2019b

I have an App Designer script in 2019b. I am trying to use a while loop to allow the user to add a file to the path before proceeding OR exit the app. The code is:

MFC_app_dir = fileparts(which('var.m'))

while length(MFC_app_dir) == 0

quit_choice = uiconfirm(app.GPSDB_Simulink, 'var.m not found in Matlab Path!', 'Exit Dialog', ...

'Options',{'Fixed, continue', 'Exit this app'}, ...

'DefaultOption',1, 'Icon', 'Warning');

if strcmpi(quit_choice, 'Exit this app')

app.delete;

return;

else

MFC_app_dir = fileparts(which('var.m')) % Check if the path has been updated

end

end

I manually add the file to the path, but the while loop does not exit. MFC_app_dir still shows up as empty even though the path has been updated. I'd appreciate some guidance on what silly mistake I'm making, TIA.

Joe

Answer 1

[Les Beckham]

I would actually expect that your while loop wouldn't execute at all, since var.m is a standard Matlab command for calculating variance.

MFC_app_dir = fileparts(which('var.m'))

MFC_app_dir = '/MATLAB/toolbox/matlab/datafun'

while length(MFC_app_dir) == 0
    disp('Entered the while loop')
end

See? It didn't enter the loop.

I would suggest using a different filename.

Also fileparts is unnecessary. It gives almost the same result as which by itself.

which('var.m')

/MATLAB/toolbox/matlab/datafun/var.m

I would probably use exist instead and force it to look in the current folder (or wherever the file is supposed to be).

Example

if exist(fullfile(pwd, 'filename.m'), 'file')
    disp('found the file')
else
    % display your uiconfirm dialog 
end

[Prabhakar Vallury]

Ugh, I replaced the actual file-name (long!) with var.m in the above post only. Forgot it's a builtin. Let's consider it as 'xyzzy.m :) :)

MFC_app_dir = fileparts(which('xyzzy.m'))
% If this is valid, it skips past the while loop.

    while length(MFC_app_dir) == 0
        quit_choice = uiconfirm(app.GPSDB_Simulink, 'xyzzy.m not found in Matlab Path!', 'Exit Dialog', ...
            'Options',{'Fixed, continue', 'Exit this app'}, ...
            'DefaultOption',1, 'Icon', 'Warning');
        if strcmpi(quit_choice, 'Exit this app')
            app.delete;
            return;
        else
            MFC_app_dir = fileparts(which('xyzzy.m'))   % Check if the path has been updated
        end
    end

Variable MFC_app_dir sets correctly if I add xyzzy.m to the path BEFORE running the app. Code skips past the 'while' loop. So that check is working fine.

But once inside the while loop, MFC_app_dir doesn't get set even when I manually add 'xyzzy.m' to the path.

[Les Beckham]

Understood.

Did you try changing the test to use exist instead of which? I think that which might not be rescanning the filesystem while your code is running, while exist(fullfile(pwd, 'filename.m'), 'file') should.

Another thing that might help is to add a short pause (perhaps pause(1)) at the bottom of the while loop to allow things to update between tests. You could try this first before switching to using exist.

[Prabhakar Vallury]

The exist command seems to assume the file would exist in the working directory (pwd)? In my particular case, the file could be in any folder -I believe the which command will return the full path of the file if it is in the Matlab path?

For that reason, I'm using the fileparts function - to get back this complete path of this file wherever it is located.

I'll try the different options and let you know - thanks for yout time.

[Walter Roberson]

isfile() and exist with 'file' option will (only) look in a particular directory if you specify a directory. isfile() in particular is documented as also looking on the matlab path if the file is not in the current directory.

[Prabhakar Vallury]

I modified the code as below and it still doesn't work. i.e., does not leave the while loop. In the command window, I'm also manually tried these 2:

1) Added xyzzy.m to the path. exist('xyzzy.m') returns 2

2) Removed xyzz.m from the path. exist('xyzzy.m') returns 0

MFC_check_path = exist('xyzzy.m');
            
while MFC_check_path == 0
    quit_choice = uiconfirm(app.GPSDB_Simulink, 'xyzzy.m not found in Matlab Path!', 'Exit Dialog', ...
        'Options',{'Fixed, continue', 'Exit this app'}, ...
        'DefaultOption',1, 'Icon', 'Warning');
    if strcmpi(quit_choice, 'Exit this app')   % Selecting the Exit button closes the app
        app.delete;
        return;
    else
        MFC_check_path = exist('xyzzy.m')   % This returns 0 even after file is added to the path
    end
end

[Les Beckham]

I think what you need to do is use exist to see if the file exists and then, if it does, use your original approach to find out where it is.

filefound = (exist('xyzzy.m', file) == 2);
            
while ~filefound
    quit_choice = uiconfirm(app.GPSDB_Simulink, 'xyzzy.m not found in Matlab Path!', 'Exit Dialog', ...
        'Options',{'Fixed, continue', 'Exit this app'}, ...
        'DefaultOption',1, 'Icon', 'Warning');
    if strcmpi(quit_choice, 'Exit this app')   % Selecting the Exit button closes the app
        app.delete;
        return;
    else
        filefound = (exist('xyzzy.m', file) == 2);
    end
end
% Now we have found the file; where is it?
MFC_app_dir = fileparts(which('xyzzy.m'))

Answer 2

[Prabhakar Vallury]

OK, I figured it out. 'uiconfirm' is a modal dialog, so all other actions are disabled until it is closed. Further, I cannot find a way to get the handle of this dialog to close it programmatically.

Seems Matlab doesn't have non-modal dialogs that come with multiple options - except 'uigetpref' which has a 'Do not show again' checkbox that I don't like at all. So I'll have to rethink my whole approach. Thanks for the insights and participation!

[Walter Roberson]

https://www.mathworks.com/help/releases/R2019b/matlab/ref/uiconfirm.html

uiconfirm(f,message,title) displays a modal in-app confirmation dialog box in target figure f. The target figure must be created with the uifigure function. This syntax displays two options for the user to select, OK and Cancel. The figure behind the dialog box is not accessible while the dialog box is displaying, but the MATLAB® command prompt is accessible.

(emphasis added)

Therefore, you should be able to make changes to the base workspace and to global variables when uiconfirm is up. At least in theory.

[Les Beckham]

I don't see that you are needing to do anything while that dialog is displayed except wait for the user to copy the file (presumably using the OS), or select Exit.

That seems like an odd user interaction to me, but I don't see why it wouldn't work.

[Prabhakar Vallury]

What I'm trying is allow the user to add the file to the Matlab path. But it appears the path is not refreshing while the uiconfirm dialog box (which is modal) is open. I can also confirm the command window is not active. When I had the dialog open, typing 'a = 1' did not return anything It did after closing the dialog. Puzzling behaviour, this seemingly little thing is taking forever. :)