error: forward declaration of 'class QLabel'

../untitled/finddialog.cpp: In constructor 'FindDialog::FindDialog(QWidget*)':
../untitled/finddialog.cpp:7:45: error: invalid use of incomplete type 'class QLabel'
label = new QLabel(tr("Find &what:"));
^
In file included from ../untitled/finddialog.cpp:2:0:
../untitled/finddialog.h:6:7: error: forward declaration of 'class QLabel'
class QLabel;
^

#include<QtGui>改成
#inlcude<QtWidgets>

Qt官网wiki有说明：http://qt-project.org/wiki/Transition_from_Qt_4.x_to_Qt5