Hello,
I understand that you are trying to create an app which invokes a function based on the timer, but the timer object is getting deleted as you close the app. App designer deletes all its workspace data when you close an app, here the timer you have started is running and when you close the app, MATLAB would automatically stop the timer by force and deletes it.
App designer provides a “closeRequest” callback function, which you can find in the callbacks section when you right click the UIFigure in App designer. You can use that function and export your app designer timer variable to MATLAB base workspace using the “assignin” function. This would help you solve your timer closing problem.
Refer this on how to change the “closeRequest” callback function: https://in.mathworks.com/support/search.html/answers/229375-how-to-change-the-closerequestfcn.html
Hope this helps!!
