Multiwindow app: runStartupFcn does not execute startupFcn on called app

I am writing an app with App Designer, that has a button to call an external app and perform some operations. I followed the instructions provided at Create Multiwindow Apps in App Designer.

I create the external app and tested its correct functioning by using another simple test app I created, containing a single button. I verified that all inputs and outputs are passed correctly between these two apps and that the startupFcn of the external app is correctly executed.

Now I tried to include the call to this external app in a more complex app and I got an unexpected issue: the external app opens, but its startupFcn is not getting executed. I traced the problem to the uneditable part of the external app, executed during the construction of the app:

% Execute the startup function
            runStartupFcn(app, @(app)startupFcn(app, varargin{:}))

When I call the external app from the test app this command correctly executes the startupFcn, but when I call it from the more complex app, runStartupFcn does not execute it and does not throw any warning or error message.

I could not find any documentation on runStartupFcn. How this function decides if it executes the startupFcn?

[Walter Roberson]

The documentation that exists seems to be https://www.mathworks.com/help/matlab/creating_guis/app-designer-startup-function.html

[Pierdavide Coïsson]

Thank you, I already read that documentation, but it does not explain runStartupFcn.

[Walter Roberson]

runStartupFcn turns on handle visibility for the app, runs the provided function handle, and turns handle visibility off again.

The execution layer is within toolbox/matlab/appdesigner/appdesigner/runtime/+appdesigner/+internal/+service/AppManagementService.m near line 122, and the direct invocation is to toolbox/matlab/appdesigner/appdesigner/runtime/+matlab/+apps/AppBase.m near line 68

There is no documentation for it because it is internal functionality not intended to be invoked directly by the user.

[Pierdavide Coïsson]

Thank you Walter. With your answers I could realize that AppManagementService.m and AppBase.m had been updated since the release R2020b I was using. I updated MATLAB to R2022a and this problem does not appear anymore. Both calls to this app from the other two apps make its startupFcn to be executed.