Getting started with CMake ◦ Building a reusable QML module

Building a QML application

In Building a C++ console application we showed the CMakeLists.txt file for a simple console application. We will now create a QML application that uses the Qt Quick module.

This is the full project file:

 cmake_minimum_required(VERSION 3.16)

 project(hello VERSION 1.0 LANGUAGES CXX)

 find_package(Qt6 6.2 COMPONENTS Quick Gui REQUIRED)

 qt_standard_project_setup(REQUIRES 6.5)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)

 qt_add_executable(myapp
     main.cpp
 )

 qt_add_qml_module(myapp
     URI hello
     QML_FILES
         main.qml
         FramedImage.qml
     RESOURCES
         img/world.png
 )

 target_link_libraries(myapp PRIVATE Qt6::Gui Qt6::Quick)

Let's walk through the changes we have made. In the find_package call, we replace Core with Quick. This will locate the Qt6Quick module and provide the Qt6::Quick targets we later link against.

 find_package(Qt6 6.2 COMPONENTS Quick Gui REQUIRED)

We call qt_standard_project_setup, and specify CMAKE_CXX_STANDARD, and CMAKE_CXX_STANDARD_REQUIRED. By passing REQUIRES 6.5 to qt_standard_project_setup, we opt-in to useful defaults for qt_add_qml_module. It enables all the Qt CMake policies up to version 6.5, in particular QTP0001 that defines a sane default resource prefix for QML modules.

 qt_standard_project_setup(REQUIRES 6.5)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)

Note that the application will still link against Qt6::Core, because Qt6::Quick depends on it.

qt_add_executable creates and finalizes an application target:

 qt_add_executable(myapp
     main.cpp
 )

qt_add_qml_module passes the target of the executable, a URI, module version, and a list of QML files to ensure that myapp becomes a QML module. This places the QML files into qrc:/qt/qml/${URI} in the resource file system. Moreover, qt_add_qml_module ensures that qmlcachegen runs. Additionally, it creates a myapp_qmllint target, which runs qmllint on the files in QML_FILES.

 qt_add_qml_module(myapp
     URI hello
     QML_FILES
         main.qml
         FramedImage.qml
     RESOURCES
         img/world.png
 )

By adding the referenced resources, they get automatically added to the application under the same root path as the QML files – also in the resource file system. By keeping the path in the resource system consistent with the one in the source and build directory, we ensure that the image is always found, as it is resolved relative to FramedImage.qml. It refers to the image in the resource file system if we load main.qml from there, or to the one in the actual file system if we review it with the qml tool.

In the target_link_libraries command, we link against Qt6::Quick instead of Qt6::Core.

 target_link_libraries(myapp PRIVATE Qt6::Gui Qt6::Quick)

Getting started with CMake ◦ Building a reusable QML module