Raspberry Pi 4B qtcreator error QGuiApplication not found

[MathewV]

I have raspberry Pi 4 B with 2021-05-07-raspios-buster-armhf-full , os installed in SD card
Further i have installed Qt with following commands after
sudo apt-get install qt5-default
sudo apt-get install qtcreator

i launch qtcreator from terminal and select Qt Quick application empty
Then in main.cpp i find
QGuiApplication not found
QQmlApplicationEngine not found

[jsulm]

@MathewV Did you include QGuiApplication and QQmlApplicationEngine header files?
You also need "QT += gui" in your pro file.
For QQmlApplicationEngine you also need QT += qml in pro file.

[MathewV]

@jsulm
Yes sir
#include <QGuiApplication>
#include <QQmlApplicationEngine>

[MathewV]

Yes sir, since I have selected Qt Quick application empty and clicked on "next " as the buttons followed

the header where included by default in main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>

and i inserted
QT += qui
QT += qml
in pro file

When i launch qtcreator from terminalopen qmain.cpp file, I get the warning
This file is not part of any projects,
and there are red circle markers along the left border of the code right from
#include <QGuiApplication>
#include <QQmlApplicationEngine>

[jsulm]

@MathewV said in Raspberry Pi 4B qtcreator error QGuiApplication not found:

This file is not part of any projects

You have to open the PROJECT file, not cpp. It's the file with.pro extension.

[MathewV]

@jsulm
Sir My problem is solved
As mentioned by you, in MyProject.pro I inserted
QT += gui
QT += qml

but still i was getting error of Unknown module(s) in QT: quick qml
then in terminal i executed
sudo apt-get install qtdeclarative5-dev
rebooted the RPi
From terminal window executed qtcreator
Opened my recent project and by Gods grace no error
Thank you @jsulm for your support, God Bless You