Need to test the validity of an application handle

I call a data application from my main application and store the data app handle in a main app local variable.. The data app has a Close button which first sets the handle to [] (by using the callingApp handle and then deletes itself. This works fine, no problem.

The probem occurs when the user closes the data app window using the "X" in the upper r/h corner. This action does execute the delete callback, but I'm unable to add code to this callback to also empty the data app handle. I'd prefer the user not use the "X", but it's impossible to prevent him from doing so inadvertently.

Isvalid would do the trick, but it's not available in 2022b. I could upgrade to 2023a, but I'd prefer not doing so at this time. An solutions?

Answer 1

[Adam Danz]

> I'd prefer the user not use the "X", but it's impossible to prevent him from doing so inadvertently.

You can set the [x] close button to be unresponsive to clicks.

uif = uifigure('CloseRequestFcn',[])

Or display an alert box to inform the user to use the app's close button

uif = uifigure('CloseRequestFcn',@(f,~)uialert(f,'Use the app''s close button','No-Can-Do'))

To close these figures

close(uif,'force')
% or 
delete(uif)

or, if you lose the handle, this deletes all figures

close all force

[Richard]

I thought there might be a callback for the "X", but wasn't able to find it. That will do the trick.

Answer 2

[Walter Roberson]

Isvalid would do the trick, but it's not available in 2022b.

isvalid with lower-case I has been available since at least 2006.

[Richard]

I can't look at the code from this computer, but I know I've tried lower case without succes. I didn't realize there was an upper case function elsewhere in the various toolboxes. The "Isvalid" in my original question is only capitalized due to force of habit.

Below is the error I receive in 2022B with the correct lower case.

'isvalid' requires one of the following:

Industrial Communication Toolbox

Image Acquisition Toolbox

Instrument Control Toolbox

Error in W3DPlot/UIAxesButtonDown (line 668)

if ~isvalid(app.hWdataPoint)

Error in matlab.apps.AppBase>@(source,event)executeCallback(ams,app,callback,requiresEventData,event) (line 62)

newCallback = @(source, event)executeCallback(ams, ...

Error while evaluating UIAxes ButtonDownFcn.

[Walter Roberson]

I am running R2022b. isvalid() exists in a large number of methods, including handle class; https://www.mathworks.com/help/matlab/ref/handle.isvalid.html

If it is telling you that you need one of those toolboxes, we might guess that whatever app.hWdataPoint is is not a handle. What shows up for class(app.hWdataPoint) at that point ? And ishandle(app.hWdataPoint) and isa(app.hWdataPoint, 'handle') ?