Find Package Failed for MQTT Simple Application

[xpress_embedo]

Hello Everyone,
I wanted to test the simple MQTT application from the example project.
But things are not working well for me.
As per the documentation, available on this https://doc.qt.io/qt-6.2/qtmqtt-index.html page.
I have to use the following in my CMakeLists.txt file, and I updated my file as below.

cmake_minimum_required(VERSION 3.16)

project(MQTT_Application VERSION 0.1 LANGUAGES CXX)

set(CMAKE_AUTOMOC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.2 COMPONENTS Quick REQUIRED)
find_package(Qt6 REQUIRED COMPONENTS Mqtt)

qt_add_executable(appMQTT_Application
    main.cpp
)

qt_add_qml_module(appMQTT_Application
    URI MQTT_Application
    VERSION 1.0
    QML_FILES main.qml 
)

set_target_properties(appMQTT_Application PROPERTIES
    MACOSX_BUNDLE_GUI_IDENTIFIER my.example.com
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(appMQTT_Application
    PRIVATE Qt6::Quick)

target_link_libraries(appMQTT_Application
    PRIVATE Qt6::Mqtt)

install(TARGETS appMQTT_Application
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})

But, I am getting the following error.

/home/xpress_embedo/Work/ESP32/ControlDevicesMQTT/MQTT_Application/CMakeLists.txt:9: error: Found package configuration file: /opt/Qt/6.2.4/gcc_64/lib/cmake/Qt6/Qt6Config.cmake but it set Qt6_FOUND to FALSE so package "Qt6" is considered to be NOT FOUND.  Reason given by package: Failed to find Qt component "Mqtt". Expected Config file at "/opt/Qt/6.2.4/gcc_64/lib/cmake/Qt6Mqtt/Qt6MqttConfig.cmake" does NOT exist```

As can be seen in the above logs, the Qt version is 6.2.4
Can someone help me with this issue?

[xpress_embedo]

@SGaist Thank You for your answer. I still find it difficult, but finally, I am able to fix this, with your help and some help from StackOverflow.
I am pasting the link which helps me below.
https://stackoverflow.com/questions/68928310/build-specific-modules-in-qt6-i-e-qtmqtt/71984521?noredirect=1#comment132724929_71984521

One Question, on the documentation page, 4 examples are given, from where can I download them?

This video can help others
https://youtu.be/DGB0GfFRqPo
And also the below-mentioned link.
https://embeddedlaboratory.blogspot.com/2023/01/getting-started-with-mqtt-using-qt.html

[SGaist]

Hi,

Did you build and install the module before using it ?

[xpress_embedo]

@SGaist Sorry I am new to Qt, I have not done anything except the steps which is shared on the documentation page.
Can you please share the documentation or some steps how to do it?

[SGaist]

Usual cmake build commands:

mkdir build_qtmqtt
cd build_qtmqtt
/path/to/Qt6/bin/qt-cmake /path/to/qtmqtt_sources/
/path/to/Qt6/bin/qt-cmake -build . -parallel
/path/to/Qt6/bin/qt-cmake install

[xpress_embedo]

@SGaist said in Find Package Failed for MQTT Simple Application:

Usual cmake build commands:

mkdir build_qtmqtt
cd build_qtmqtt
/path/to/Qt6/bin/qt-cmake /path/to/qtmqtt_sources/
/path/to/Qt6/bin/qt-cmake -build . -parallel
/path/to/Qt6/bin/qt-cmake install

Thank You for some hints, I have a very basic understanding of CMake, and I will share what I have done till now, and maybe you can give me some more hints to fix my problem.
Qt MQTT module link is this: https://code.qt.io/cgit/qt/qtmqtt.git/
As a first step, I cloned this module using the command git clone https://code.qt.io/cgit/qt/qtmqtt.git, and after cloning I switched to branch 6.2.4, as this is the Qt version installed on my laptop.
I opened the terminal and tried to configure the project using the following command.

mkdir build
cd build
/opt/Qt/Tools/CMake/bin/cmake ..

And I get the following error, also shown in the screenshot below.

CMake Error at CMakeLists.txt:19 (find_package):
  Could not find a package configuration file provided by "Qt6" (requested
  version 6.2.4) with any of the following names:

    Qt6Config.cmake
    qt6-config.cmake

  Add the installation prefix of "Qt6" to CMAKE_PREFIX_PATH or set "Qt6_DIR"
  to a directory containing one of the above files.  If "Qt6" provides a
  separate development package or SDK, be sure it has been installed.


-- Configuring incomplete, errors occurred!
See also "/home/xpress_embedo/Work/Qt/DontCommit/qtmqtt/build/CMakeFiles/CMakeOutput.log".

From the message, it is clear that qt6-config.cmake is missing, and I think the reason is obvious, as I have to provide the path of this.
Anyways, as a next step, what I did is, I opened the project in QtCreator and builds it and it build properly.

As per the message the library is created successfully.
[31/31 4.1/sec] Creating library symlink lib/libQt6Mqtt.so.6 lib/libQt6Mqtt.so
I think CMake is also going to do the same thing, but what are the next steps, how can I use this library?
Another question is why the steps mentioned in the documentation page is different.
https://doc.qt.io/qt-6/qtmqtt-index.html

Sorry for stupid questions, I am trying to learn.

[SGaist]

1. the path I used in my example above was on purpose. Look into your Qt 6.2.4 folder, you'll find qt-cmake in the bin folder. That would have avoided the round trip through Qt Creator. Note that it's not wrong to use Qt Creator at all, I am just used to the terminal.
2. Either add a custom step that calls cmake install or do it on the terminal as shown above.
3. the instructions in the documentation are for using the module and are correct from that point of view.

[xpress_embedo]

@SGaist Thank You for your answer. I still find it difficult, but finally, I am able to fix this, with your help and some help from StackOverflow.
I am pasting the link which helps me below.
https://stackoverflow.com/questions/68928310/build-specific-modules-in-qt6-i-e-qtmqtt/71984521?noredirect=1#comment132724929_71984521

One Question, on the documentation page, 4 examples are given, from where can I download them?

This video can help others
https://youtu.be/DGB0GfFRqPo
And also the below-mentioned link.
https://embeddedlaboratory.blogspot.com/2023/01/getting-started-with-mqtt-using-qt.html

[SGaist]

They are in the sources you already cloned.