Qt creator cannot find, QTcpServer and QTcpSocket - c++

Question

Eventhough, I put 'network' in .pro file,
My Qt creator cannot find QTcpSocket and QTcpServer.
What should I do?
I remove the Qtcreator and redownloaded already but it also did not work.
My Linux version is Ubuntu 14.04 LTS
and I downloaded QT Creator by linux commands.
sudo apt-get install qtcreator
I even do the linus updates because I worried that I missed something.
sudo get-apt update
sudo get-apt upgrade
Why Qtcreator cannot perceive QTcpServer and QTcpSocket headers?
--------------*.pro -----------------------------------
QT += core gui network
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = server11
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp
HEADERS += mainwindow.h
FORMS += mainwindow.ui
-------------------mainwindow.h--------------------------------------
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QTcpSocket>
#include <QTcpServer>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

Answer 1

Did you install the complete framework? Or just the IDE?
Try downloading the Qt offline installer and downloading the framework through it. Download and install it from here.
Qt Open Source
Instructions for Ubuntu