mainwindow.pro Example File
mainwindows/mainwindow/mainwindow.pro
  TEMPLATE = app
  QT += widgets
  HEADERS += colorswatch.h mainwindow.h toolbar.h
  SOURCES += colorswatch.cpp mainwindow.cpp toolbar.cpp main.cpp
  build_all:!build_pass {
      CONFIG -= build_all
      CONFIG += release
  }
  RESOURCES += mainwindow.qrc
  # install
  target.path = $$[QT_INSTALL_EXAMPLES]/widgets/mainwindows/mainwindow
  INSTALLS += target