waitfordata

Imagine you have a GUI that saves some data you want in an APPDATA field named 'points'. You can get that field using: getappdata(f, 'points'), but this gives you no guarantee that the user is actually done with the GUI; you don't know if POINTS is in a finished state yet.

If you instead run: data = waitfordata(f, {'points'}); points = data{1}, you now block execution until the GUI is closed, but grab the points data from the GUI just as it is closing. You have a guarantee that points will be set with the data only after the user finished with the GUI.