Today,when I analyzed the ui_displaydialog.h which was created automatically by qmake,I

found something important:
qmake read from .ui file then it created a new file based on .ui.It usually declare a

new class likes Ui_XXXX.In this class,it usually declare a public function class called "setupUi".Its functions is to create all the components and layout them.
We can check out the file "ui_displaydialog.h"