How can I put a stopwatch that counts how much time has passed since opening an app?

Hi everyone, I searched the net but unfortunately I didn't understand how to do it. What I would like to do is quite simple:

I want to measure the time that passes since I open an app and, if it exceeds a certain threshold (e.g. 3 minutes), then I have to assign the value 1 to a variable.

Thanks in advance,

Lorenzo

Answer 1

[Adam Danz]

> I want to measure the time that passes since I open an app

Create a timer object in the startup function of the App and start the timer at the end of the startup function. Set the timer callback function to update the variable after 3 minutes. The variable should be stored within the app, either as an app component or as a public property.

Timers can be tricky to set up if you haven't done so before so I recommend reading the links I provided to get a sense of how the timer will work. If you get stuck, specifically indicate what step you're stuck on, what you tried, and I'd be happy to help set things straight.

Add timer to App that starts when app opens and changes variable after a fixed delay

See attached timerDemo.mlapp which contains these 4 steps.

1. Declare the timer and the variable to be updated as a private property (or public, if needed). Alternatively, the variable to be updated might be an app component such as a text field which would not need to be declared as an app propery.

properties (Access = private) 
    startupTimer         % timer obj created in startupFcn
    timeExpired = 0;     % updated by app.startupTimer
end 

2. Create timer in startupFcn(); start the timer at the end of the startupFcn.

function startupFcn(app)
    app.startupTimer = timer('Name','startupTimer','ExecutionMode','singleShot', ...
        'ObjectVisibility','off','StartDelay',3*60, ...      %StartDelay is in seconds
        'TimerFcn',@(~,~)updateValue(app,1));
    start(app.startupTimer) % <--- at the end of the startupFcn
end

To run the same timer again, just execute start(app.startupTimer).

3. Define the variable-update function that is evoked by the timer after the StartDelay (how to add helper function)

function updateValue(app,TF)
    % Evoked by app.startupTimer; sets app.timeExpired to the value in TF. 
    app.timeExpired = TF;             
end

4. Delete the timer when the app closes. Add a close request function to the app.

% Close request function: UIFigure
function UIFigureCloseRequest(app, event)
    delete(app.startupTimer)
    delete(app)
end

[Lorenzo Corso]

First of all, thank you very much for the comprehensive answer. However he gives me this error as soon as the 3 minutes pass

(what I put in matlab was exactly what you wrote)

[Adam Danz]

That must be happening in the updateValue function, correct?

Is that function defined within app designer code? The variable "app" must be used all throughout your app or it would have thrown errors elsewhere so I can't imagine what woud cause that error if the function is defined within AppDesigner. .

If you can run the demo I attached without error, then you know there's something wrong with your implementation.

If the function is defined within app designer, please attach the app.

[Lorenzo Corso]

Yes I'm working on app designer. I apologize for wasting your time because the problem was not in your code. I don't know why yet but I have problems with that app (eg if I move buttons it doesn't work anymore). Thanks so much for the explanation and have a nice day :)

[Adam Danz]

In case you're already not familiar with debugging methods in AppDesigner, here's a quick reminder:

https://www.mathworks.com/matlabcentral/answers/499633-how-to-view-parameter-values-while-debugging-in-app-designer#answer_409464

You got this!