why i must include "Qtwidget/" in some project?

[qazaq408]

qt5.15 + vs2019

i create some Qt projects, int most time , i only write #include 'QDialog'. But a few Projects, i need to write "#include 'QtWidgets/QDialog' "，if i write "#include ' QDialog' ", vs2019 tell me "Can't open file 'QDialog' ".

i confirm (many times) i had set the vs2019, "Proprety->Qt Project Settings->Qt Modules", and selected "core;gui;widget".

So why i must use "QtWdiget/QDialog" but not "QDialog" int a few projects?

[qazaq408]

i get it,set system path