Typically the main app starts a child app and hold its app instance. If the main app will be closed the child app should be closed too by the close callback.
properties (Access = private)
childApp % declare private property
end
...
app.childApp = ChildApp(<arg>) % start child app somewhere
...
function CloseRequest(app)
app.childApp.delete % close the child app first
app.delete % close the main app
end
