How to check if another window is running?

Question

MATLAB

Good afternoon. I am writing a program with a multi-window interface in matlab, I actively use GUIDE, I transfer / receive data between windows (from parent to child) using the setappdata and getappdata functions, for example, as follows:

setappdata(findobj('Tag', 'mainWindow'), 'DataNew', get(handles.editDataNew, 'String'))

When debugging each window separately (child windows are not modal and can be launched on their own) from the parent, I have to check for the presence of a running parent window with the 'mainWindow' tag in order to perform setappdata, otherwise perform other actions. Please tell me how to check if the window with the 'mainWindow' tag is running?